M7(R2) Assessment and 
Control of DNA Reactive 
(Mutagenic) Impurities in 
Pharmaceuticals to Limit 
Potential Carcinogenic Risk 
Guidance for Industry 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Drug Evaluation and Research (CDER) 
Center for Biologics Evaluation and Research (CBER) 
 
July 2023 
ICH-Multidisciplinary
  Contains Nonbinding Recommendations 
M7(R2) Assessment and 
Control of DNA Reactive 
(Mutagenic) Impurities in 
Pharmaceuticals to Limit 
Potential Carcinogenic Risk 
Guidance for Industry 
 
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https://www.fda.gov/vaccines-blood-biologics/guidance-compliance-regulatory-information-biologics/biologics-guidances 
 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Drug Evaluation and Research (CDER) 
Center for Biologics Evaluation and Research (CBER) 
 
July 2023 
ICH-Multidisciplinary
  Contains Nonbinding Recommendations 
FOREWORD 
 
The International Council for Harmonisation of Technical Requirements for Pharmaceuticals 
for Human Use (ICH) has the mission of achieving greater regulatory harmonization 
worldwide to ensure that safe, effective, and high-quality medicines are developed, 
registered, and maintained in the most resource-efficient manner.  By harmonizing the 
regulatory expectations in regions around the world, ICH guidelines have substantially 
reduced duplicative clinical studies, prevented unnecessary animal studies, standardized 
safety reporting and marketing application submissions, and contributed to many other 
improvements in the quality of global drug development and manufacturing and the products 
available to patients.  
 
ICH is a consensus-driven process that involves technical experts from regulatory authorities 
and industry parties in detailed technical and science-based harmonization work that results 
in the development of ICH guidelines.  The commitment to consistent adoption of these 
consensus-based guidelines by regulators around the globe is critical to realizing the benefits 
of safe, effective, and high-quality medicines for patients as well as for industry.  As a 
Founding Regulatory Member of ICH, the Food and Drug Administration (FDA) plays a 
major role in the development of each of the ICH guidelines, which FDA then adopts and 
issues as guidance to industry.
  Contains Nonbinding Recommendations 
TABLE OF CONTENTS 
 
I.  INTRODUCTION (1) .................................................................................................. 1 
II.  SCOPE OF GUIDANCE (2) ....................................................................................... 2 
III.  GENERAL PRINCIPLES (3) ..................................................................................... 2 
IV.  CONSIDERATIONS FOR MARKETED PRODUCTS (4) .................................... 4 
A.  Postapproval Changes to the Drug Substance Chemistry, Manufacturing, and  
Controls (4.1) ............................................................................................................................ 4 
B.  Postapproval Changes to the Drug Product Chemistry, Manufacturing, and  
Controls (4.2) ............................................................................................................................ 4 
C.  Changes to the Clinical Use of Marketed Products (4.3) ...................................................... 5 
D.  Other Considerations for Marketed Products (4.4) .............................................................. 5 
V.  DRUG SUBSTANCE AND DRUG PRODUCT IMPURITY ASSESSMENT (5) . 5 
A.  Synthetic Impurities (5.1) ........................................................................................................ 6 
B.  Degradation Products (5.2) ..................................................................................................... 6 
C.  Considerations for Clinical Development (5.3) ..................................................................... 7 
VI.  HAZARD ASSESSMENT ELEMENTS (6) .............................................................. 7 
VII.  RISK CHARACTERIZATION (7) ............................................................................ 9 
A.  TTC-based Acceptable Intakes (7.1) ...................................................................................... 9 
B.  Acceptable Intakes Based on Compound-Specific Risk Assessments (7.2) ........................ 9 
1. Mutagenic Impurities With Positive Carcinogenicity Data (Class 1 in Table 1) (7.2.1) ........... 9 
2. Mutagenic Impurities with Evidence for a Practical Threshold (7.2.2) .................................... 9 
C.  Acceptable Intakes in Relation to LTL Exposure (7.3) ...................................................... 10 
1. Clinical Development (7.3.1) ................................................................................................... 10 
2. Marketed Products (7.3.2) ....................................................................................................... 11 
D.  Acceptable Intakes for Multiple Mutagenic Impurities (7.4) ............................................. 11 
E.  Exceptions and Flexibility in Approaches (7.5) ................................................................... 11 
VIII.  CONTROL (8) ............................................................................................................ 12 
A.  Control of Process-Related Impurities (8.1) ........................................................................ 13 
B.  Considerations for Control Approaches (8.2) ..................................................................... 14 
C.  Considerations for Periodic Testing (8.3) ............................................................................ 15 
D.  Control of Degradation Products (8.4) ................................................................................. 15 
E.  Lifecycle Management (8.5) .................................................................................................. 15 
F.  Considerations for Clinical Development (8.6) ................................................................... 16 
IX.  DOCUMENTATION (9) ........................................................................................... 17 
A.  Clinical Trial Applications (9.1) ........................................................................................... 17 
B.  Common Technical Document (Marketing Application) (9.2) .......................................... 17 
NOTES .................................................................................................................................... 18 
i  Contains Nonbinding Recommendations 
GLOSSARY............................................................................................................................ 23 
REFERENCES ....................................................................................................................... 25 
APPENDIX 1: SCOPE SCENARIOS  FOR APPLICATION OF THE ICH M7(R2) 
GUIDANCE ............................................................................................................................ 27 
APPENDIX 2:  CASE EXAMPLES  TO ILLUSTRATE POTENTIAL CONTROL 
APPROACHES ...................................................................................................................... 29 
APPENDIX 3: LIST OF COMPOUNDS IN ICH M7(R2) ADDENDUM: 
ACCEPTABLE INTAKES OR PERMISSIBLE DAILY EXPOSURES ......................... 31 
 
ii  Contains Nonbinding Recommendations 
M7(R2) Assessment and Control  
of DNA Reactive (Mutagenic) Impurities  
in Pharmaceuticals to Limit Potential Carcinogenic Risk 
Guidance for Industry1 
 
 
 
This guidance represents the current thinking of the Food and Drug Administration (FDA or Agency) 
on this topic.  It does not establish any rights for any person and is not binding on FDA or the public.  
You can use an alternative approach if it satisfies the requirements of the applicable statutes and 
regulations.  To discuss an alternative approach, contact the FDA office responsible for this guidance 
as listed on the title page.   
 
 
 
I.  INTRODUCTION (1)2 
 
The synthesis of drug substances involves the use of reactive chemicals, reagents, solvents, 
catalysts, and other processing aids. As a result of chemical synthesis or subsequent 
degradation, impurities reside in all drug substances and associated drug products. Although 
the International Council for Harmonisation (ICH) guidances for industry Q3A Impurities in 
New Drug Substances (Revision 2) (ICH Q3A) (June 2008) and Q3B(R2) Impurities in New 
Drug Products (ICH Q3B(R2)) (August 2006) (Reference (Ref.) 1, 2) provide guidance for 
qualification and control for the majority of the impurities,3 limited guidance is provided for 
those impurities that are DNA reactive. The purpose of this guidance is to provide a practical 
framework that is applicable to the identification, categorization, qualification, and control of 
these mutagenic impurities to limit potential carcinogenic risk. This guidance is intended to 
complement ICH Q3A, ICH Q3B(R2) (Note 1), and the ICH guidance for industry M3(R2) 
Nonclinical Safety Studies for the Conduct of Human Clinical Trials and Marketing 
Authorizations for Pharmaceuticals (January 2010) (Ref. 3). 
 
This guidance emphasizes considerations of both safety and quality risk management in 
establishing levels of mutagenic impurities that are expected to pose negligible carcinogenic 
risk. It outlines recommendations for assessment and control of mutagenic impurities that 
reside or are reasonably expected to reside in final drug substance or product, taking into 
consideration the intended conditions of human use. 
 
In general, FDAs guidance documents do not establish legally enforceable responsibilities. 
Instead, guidances describe the Agencys current thinking on a topic and should be viewed 
only as recommendations, unless specific regulatory or statutory requirements are cited. The 
 
1 This guidance was developed within the Expert Working Group (Multidisciplinary) of the International 
Council for Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use 
(ICH) and has been subject to consultation by the regulatory parties, in accordance with the ICH process. This 
document has been endorsed by the ICH Assembly at Step 4 of the ICH process, April 2023. At Step 4 of the 
process, the final draft is recommended for adoption to the regulatory bodies of the ICH regions. 
2 The numbers in parentheses reflect the organizational breakdown of the document endorsed by the ICH 
Assembly at Step 4 of the ICH process, April 2023. 
3 We update guidances periodically. To make sure you have the most recent version of a guidance, check the 
FDA guidance web page at https://www.fda.gov/regulatory-information/search-fda-guidance-documents.  
1  Contains Nonbinding Recommendations 
use of the word should in Agency guidances means that something is suggested or 
recommended, but not required. 
 
 
II.  SCOPE OF GUIDANCE (2) 
 
This document is intended to provide guidance for new drug substances and new drug 
products during their clinical development and subsequent applications for marketing. It also 
applies to postapproval submissions of marketed products, and to new marketing applications 
for products with a drug substance that is present in a previously approved product, in both 
cases only where: 
 
  Changes to the drug substance synthesis result in new impurities or increased 
acceptance criteria for existing impurities 
 
  Changes in the formulation, composition, or manufacturing process result in new 
degradation products or increased acceptance criteria for existing degradation 
products 
 
  Changes in indication or dosing regimen are made, which significantly affect the 
acceptable cancer risk level 
 
Assessment of the mutagenic potential of impurities as described in this guidance is not 
intended for the following types of drug substances and drug products: 
biological/biotechnological, peptide, oligonucleotide, radiopharmaceutical, fermentation 
products, herbal products, and crude products of animal or plant origin. 
 
This guidance does not apply to drug substances and drug products intended for advanced 
cancer indications as defined in the scope of the ICH guidance for industry S9 Nonclinical 
Evaluation for Anticancer Pharmaceuticals (March 2010) (Ref. 4). Additionally, there may 
be some cases where a drug substance intended for other indications is itself genotoxic at 
therapeutic concentrations and may be expected to be associated with an increased cancer 
risk. Exposure to a mutagenic impurity in these cases would not significantly add to the 
cancer risk of the drug substance. Therefore, impurities could be controlled at acceptable 
levels for nonmutagenic impurities. 
 
Assessment of the mutagenic potential of impurities as described in this guidance is not 
intended for excipients used in existing marketed products, flavoring agents, colorants, and 
perfumes. Application of this guidance to leachables associated with drug product packaging 
is not intended, but the safety risk assessment principles outlined in this guidance for limiting 
potential carcinogenic risk can be used if warranted. The safety risk assessment principles of 
this guidance can be used if warranted for impurities in excipients that are used for the first 
time in a drug product and are chemically synthesized. 
 
 
III.  GENERAL PRINCIPLES (3) 
 
The focus of this guidance is on DNA-reactive substances that have a potential to directly 
cause DNA damage when present at low levels leading to mutations and, therefore, 
potentially causing cancer. This type of mutagenic carcinogen is usually detected in a 
2  Contains Nonbinding Recommendations 
bacterial reverse mutation (mutagenicity) assay. Other types of genotoxicants that are 
nonmutagenic typically have threshold mechanisms and usually do not pose carcinogenic risk 
in humans at the level ordinarily present as impurities. Therefore, to limit a possible human 
cancer risk associated with the exposure to potentially mutagenic impurities, the bacterial 
mutagenicity assay is used to assess the mutagenic potential and the need for controls. 
Structure-based assessments are useful for predicting bacterial mutagenicity outcomes based 
upon the established knowledge. There are a variety of approaches to conduct this evaluation 
including a review of the available literature and/or computational toxicology assessment. 
 
A threshold of toxicological concern (TTC) concept was developed to define an acceptable 
intake for any unstudied chemical that poses a negligible risk of carcinogenicity or other toxic 
effects. The methods upon which the TTC is based are generally considered to be very 
conservative because they involve a simple linear extrapolation from the dose giving a 50 
percent tumor incidence (TD ) to a 1 in 106 incidence, using TD  data for the most sensitive 
50 50
species and most sensitive site of tumor induction. For application of a TTC in the assessment 
of acceptable limits of mutagenic impurities in drug substances and drug products, a value of 
1.5 micrograms (g)/day corresponding to a theoretical 10-5 (1 in 100,000) excess lifetime 
risk of cancer can be justified. Some structural groups were identified to be of such high 
potency that intakes even below the TTC would theoretically be associated with a potential 
for a significant carcinogenic risk. This group of high-potency mutagenic carcinogens 
referred to as the cohort of concern comprises aflatoxin-like-, N-nitroso-, and alkyl-azoxy 
compounds. 
 
During clinical development, it is expected that control strategies and approaches will be less 
developed in earlier phases where overall development experience is limited. This guidance 
bases acceptable intakes for mutagenic impurities on established risk assessment strategies. 
Acceptable risk during the early development phase is set at a theoretically calculated level of 
approximately 1 additional cancer per 1 million. For later stages in development and for 
marketed products, acceptable increased cancer risk is set at a theoretically calculated level of 
approximately 1 in 100,000. These risk levels represent a small theoretical increase in risk 
when compared to human overall lifetime incidence of developing any type of cancer, which 
is greater than 1 in 3. It is noted that established cancer risk assessments are based on lifetime 
exposures. Less-than-lifetime (LTL) exposures during both development and marketing can 
have higher acceptable intakes of impurities and still maintain comparable risk levels. The 
use of a numerical cancer risk value (1 in 100,000) and its translation into risk-based doses 
(TTC) is a highly hypothetical concept that should not be regarded as a realistic indication of 
the actual risk. Nevertheless, the TTC concept provides an estimate of safe exposures for any 
mutagenic compound. However, exceeding the TTC is not necessarily associated with an 
increased cancer risk given the conservative assumptions employed in the derivation of the 
TTC value. The most likely increase in cancer incidence is actually much less than 1 in 
100,000. In addition, in cases where a mutagenic compound is a noncarcinogen in a rodent 
bioassay, there would be no predicted increase in cancer risk. Based on all the above 
considerations, any exposure to an impurity that is later identified as a mutagen is not 
necessarily associated with an increased cancer risk for subjects already exposed to the 
impurity. A risk assessment would determine whether any further actions would be taken. 
 
Where a potential risk has been identified for an impurity, an appropriate control strategy 
leveraging process understanding and/or analytical controls should be developed to ensure 
that the mutagenic impurity is at or below the acceptable cancer risk level. 
 
3  Contains Nonbinding Recommendations 
There may be cases when an impurity is also a metabolite of the drug substance. In such 
cases, the risk assessment that addresses mutagenicity of the metabolite can qualify the 
impurity. 
 
 
IV.  CONSIDERATIONS FOR MARKETED PRODUCTS (4) 
 
This guidance is not intended to be applied retrospectively (i.e., to products marketed before 
adoption of this guidance). However, some types of postapproval changes warrant a 
reassessment of safety relative to mutagenic impurities. This section applies to these 
postapproval changes for products marketed before, or after, the adoption of this guidance. 
Section VIII.E, Lifecycle Management, (8.5) contains additional recommendations for 
products marketed after adoption of this guidance. 
 
A.  Postapproval Changes to the Drug Substance Chemistry, Manufacturing, 
and Controls (4.1) 
 
Postapproval submissions involving the drug substance chemistry, manufacturing, and 
controls should include an evaluation of the potential risk impact associated with mutagenic 
impurities from changes to the route of synthesis, reagents, solvents, or process conditions 
after the starting material. Specifically, changes should be evaluated to determine if the 
changes result in any new mutagenic impurities or higher acceptance criteria for existing 
mutagenic impurities. Reevaluation of impurities not impacted by changes is not 
recommended. For example, when only a portion of the manufacturing process is changed, 
the assessment of risk from mutagenic impurities should be limited to whether any new 
mutagenic impurities result from the change, whether any mutagenic impurities formed 
during the affected step are increased, and whether any known mutagenic impurities from 
upstream steps are increased. Regulatory submissions associated with such changes should 
describe the assessment as outlined in section IX.B (9.2). Changing the site of manufacture of 
a drug substance, intermediates, or starting materials or changing raw materials supplier will 
not require a reassessment of mutagenic impurity risk. 
 
When a new drug substance supplier is proposed, evidence that the drug substance produced 
by this supplier using the same route of synthesis as an existing drug product marketed in the 
assessors region is considered to be sufficient evidence of acceptable benefit-risk regarding 
mutagenic impurities, and an assessment per this guidance is not required. If this is not the 
case, then an assessment per this guidance is expected. 
 
B.  Postapproval Changes to the Drug Product Chemistry, Manufacturing, 
and Controls (4.2) 
 
Postapproval submissions involving the drug product (e.g., change in composition, 
manufacturing process, dosage form) should include an evaluation of the potential risk 
associated with any new mutagenic degradation products or higher acceptance criteria for 
existing mutagenic degradation products. If appropriate, the regulatory submission would 
include an updated control strategy. Reevaluation of the drug substance associated with the 
drug products is not recommended or expected provided there are no changes to the drug 
substance. Changing the site of manufacture of a drug product will not require a reassessment 
of mutagenic impurity risk. 
 
4  Contains Nonbinding Recommendations 
C.  Changes to the Clinical Use of Marketed Products (4.3) 
 
Changes to the clinical use of marketed products that can warrant a reevaluation of the 
mutagenic impurity limits include a significant increase in clinical dose, an increase in 
duration of use (in particular when a mutagenic impurity was controlled above the lifetime 
acceptable intake for a previous indication that may no longer be appropriate for the longer 
treatment duration associated with the new indication), or for a change in indication from a 
serious or life-threatening condition where higher acceptable intakes were justified (section 
VII.E (7.5)) to an indication for a less serious condition where the existing impurity 
acceptable intakes may no longer be appropriate. Changes to the clinical use of marketed 
products associated with new routes of administration or expansion into subject populations 
that include pregnant individuals and/or pediatric subjects will not warrant a reevaluation, 
assuming no increases in daily dose or duration of treatment. 
 
D.  Other Considerations for Marketed Products (4.4) 
 
Application of this guidance may be warranted to marketed products if there is specific cause 
for concern. The existence of impurity structural alerts alone is considered insufficient to 
trigger follow-up measures, unless it is a structure in the cohort of concern (section III (3)). 
However, a specific cause for concern would be new relevant impurity hazard data (classified 
as Class 1 or 2, section VI (6)) generated after the overall control strategy and specifications 
for market authorization were established. This new relevant impurity hazard data should be 
derived from high-quality scientific studies consistent with relevant regulatory testing 
guidelines, with data records or reports readily available. Similarly, a newly discovered 
impurity that is a known Class 1 or Class 2 mutagen that is present in a marketed product 
could also be a cause for concern. In both of these cases when the applicant becomes aware 
of this new information, an evaluation per this guidance should be conducted. 
 
 
V.  DRUG SUBSTANCE AND DRUG PRODUCT IMPURITY ASSESSMENT (5) 
 
Actual and potential impurities that are likely to arise during the synthesis and storage of a 
new drug substance and during manufacturing and storage of a new drug product should be 
assessed. 
 
The impurity assessment is a two-stage process: 
 
  Actual impurities that have been identified should be considered for their mutagenic 
potential. 
 
  An assessment of potential impurities likely to be present in the final drug substance 
is carried out to determine if further evaluation of their mutagenic potential is 
recommended. 
 
The steps as applied to synthetic impurities and degradation products are described in 
sections V.A (5.1) and V.B (5.2), respectively. 
 
5  Contains Nonbinding Recommendations 
A.  Synthetic Impurities (5.1) 
 
Actual impurities include those observed in the drug substance above the ICH Q3A reporting 
thresholds. Identification of actual impurities is expected when the levels exceed the 
identification thresholds outlined by ICH Q3A. It is acknowledged that some impurities 
below the identification threshold may also have been identified. 
 
Potential impurities in the drug substance can include starting materials, reagents, and 
intermediates in the route of synthesis from the starting material to the drug substance. 
 
The risk of carryover into the drug substance should be assessed for identified impurities that 
are present in starting materials and intermediates and impurities that are reasonably expected 
by-products in the route of synthesis from the starting material to the drug substance. As the 
risk of carryover may be negligible for some impurities (e.g., those impurities in early 
synthetic steps of long routes of synthesis), a risk-based justification could be provided for 
the point in the synthesis after which these types of impurities should be evaluated for 
mutagenic potential. 
 
For starting materials that are introduced late in the synthesis of the drug substance (and 
where the synthetic route of the starting material is known), the final steps of the starting 
material synthesis should be evaluated for potential mutagenic impurities. 
 
Actual impurities where the structures are known and potential impurities as defined above 
should be evaluated for mutagenic potential as described in section VI (6). 
 
B.  Degradation Products (5.2) 
 
Actual drug substance degradation products include those observed above the ICH Q3A 
reporting threshold during storage of the drug substance in the proposed long-term storage 
conditions and primary and secondary packaging. Actual degradation products in the drug 
product include those observed above the ICH Q3B(R2) reporting threshold during storage of 
the drug product in the proposed long-term storage conditions and primary and secondary 
packaging, and also include those impurities that arise during the manufacture of the drug 
product. Identification of actual degradation products is expected when the levels exceed the 
identification thresholds outlined by ICH Q3A and Q3B(R2). It is acknowledged that some 
degradation products below the identification threshold may also have been identified. 
 
Potential degradation products in the drug substance and drug product are those that may be 
reasonably expected to form during long-term storage conditions. Potential degradation 
products include those that form above the ICH Q3A and Q3B(R2) identification thresholds 
during accelerated stability studies (e.g., 40C/75 percent relative humidity for 6 months) and 
confirmatory photostability studies as described in the ICH guidance for industry Q1B 
Photostability Testing of New Drug Substances and Products (November 1996) (Ref. 5), but 
are yet to be confirmed in the drug substance or drug product under long-term storage 
conditions in the primary packaging. 
 
Knowledge of relevant degradation pathways can be used to help guide decisions on the 
selection of potential degradation products to be evaluated for mutagenicity (e.g., from 
degradation chemistry principles, relevant stress testing studies, and development stability 
studies). 
6  Contains Nonbinding Recommendations 
 
Actual and potential degradation products likely to be present in the final drug substance or 
drug product and where the structure is known should be evaluated for mutagenic potential as 
described in section VI (6). 
 
C.  Considerations for Clinical Development (5.3) 
 
It is expected that the impurity assessment described in sections V.A (5.1) and V.B (5.2) 
applies to products in clinical development. However, it is acknowledged that the available 
information is limited. For example, information from long-term stability studies and 
photostability studies may not be available during clinical development, and thus, 
information on potential degradation products may be limited. Additionally, the thresholds 
outlined in ICH Q3A and Q3B(R2) do not apply to products in clinical development and 
consequently fewer impurities will be identified. 
 
 
VI.  Hazard Assessment Elements (6) 
 
Hazard assessment involves an initial analysis of actual and potential impurities by 
conducting database and literature searches for carcinogenicity and bacterial mutagenicity 
data to classify them as Class 1, 2, or 5 according to Table 1. If data for such a classification 
are not available, an assessment of structure-activity relationships (SARs) that focuses on 
bacterial mutagenicity predictions should be performed. This could lead to a classification 
into Class 3, 4, or 5. 
 
Table 1: Impurities Classification With Respect to Mutagenic and Carcinogenic 
Potential and Resulting Control Actions 
 
Proposed action for control 
Class  Definition  (details in sections VII (7) 
and VIII (8)) 
1  Known mutagenic carcinogens  Control at or below compound-
specific acceptable limit 
2  Known mutagens with unknown  Control at or below acceptable limits 
carcinogenic potential (bacterial  (appropriate threshold of 
mutagenicity positive,* no rodent  toxicological concern (TTC)) 
carcinogenicity data) 
3  Alerting structure, unrelated to the structure  Control at or below acceptable limits 
of the drug substance;   (appropriate TTC) or conduct 
bacterial mutagenicity assay; 
no mutagenicity data 
if nonmutagenic = Class 5; if 
mutagenic = Class 2 
4  Alerting structure, same alert in drug  Treat as nonmutagenic impurity 
substance or compounds related to the drug 
substance (e.g., process intermediates), 
which have been tested and are 
nonmutagenic 
7  Contains Nonbinding Recommendations 
Proposed action for control 
Class  Definition  (details in sections VII (7) 
and VIII (8)) 
5  No structural alerts, or alerting structure  Treat as nonmutagenic impurity 
with sufficient data to demonstrate lack of 
mutagenicity or carcinogenicity 
*Or other relevant positive mutagenicity data indicative of DNA-reactivity related induction of gene mutations 
(e.g., positive findings in in vivo gene mutation studies). 
 
A computational toxicology assessment should be performed using (quantitative) SAR 
((Q)SAR) methodologies that predict the outcome of a bacterial mutagenicity assay (Ref. 6). 
Two (Q)SAR prediction methodologies that complement each other should be applied. One 
methodology should be expert rule based, and the second methodology should be statistical 
based. (Q)SAR models utilizing these prediction methodologies should follow the general 
validation principles set forth by the Organization for Economic Co-operation and 
Development (OECD). 
 
The absence of structural alerts from two complementary (Q)SAR methodologies (expert rule 
based and statistical) is sufficient to conclude that the impurity is of no mutagenic concern, 
and no further testing is recommended (Class 5 in Table 1). 
 
If warranted, the outcome of any computer system-based analysis can be reviewed with the 
use of expert knowledge to provide additional supportive evidence on relevance of any 
positive, negative, conflicting, or inconclusive prediction and provide a rationale to support 
the final conclusion. 
 
To follow up on a relevant structural alert (Class 3 in Table 1), either adequate control 
measures could be applied or a bacterial mutagenicity assay with the impurity alone could be 
conducted. An appropriately conducted negative bacterial mutagenicity assay (Note 2) would 
overrule any structure-based concern, and no further genotoxicity assessments would be 
recommended (Note 1). These impurities should be considered nonmutagenic (Class 5 in 
Table 1). A positive bacterial mutagenicity result would warrant further hazard assessment 
and/or control measures (Class 2 in Table 1). For instance, when levels of the impurity cannot 
be controlled at an appropriate acceptable limit, it is recommended that the impurity be tested 
in an in vivo gene mutation assay to understand the relevance of the bacterial mutagenicity 
assay result under in vivo conditions. The selection of other in vivo genotoxicity assays 
should be scientifically justified based on knowledge of the mechanism of action of the 
impurity and expected target tissue exposure (Note 3). In vivo studies should be designed 
taking into consideration existing ICH genotoxicity guidances. Results in the appropriate in 
vivo assay may support setting compound-specific impurity limits. 
 
An impurity with a structural alert that is shared (e.g., same structural alert in the same 
position and chemical environment) with the drug substance or related compounds can be 
considered as nonmutagenic (Class 4 in Table 1) if the testing of such material in the bacterial 
mutagenicity assay was negative. 
 
 
8  Contains Nonbinding Recommendations 
VII.  Risk Characterization (7) 
 
As a result of hazard assessment described in section VI (6), each impurity will be assigned 
to one of the five classes in Table 1. For impurities belonging in Classes 1, 2, and 3, the 
principles of risk characterization used to derive acceptable intakes are described in this 
section. 
 
A.  TTC-based Acceptable Intakes (7.1) 
 
A TTC-based acceptable intake of a mutagenic impurity of 1.5 g per person per day is 
considered to be associated with a negligible risk (theoretical excess cancer risk of less than 1 
in 100,000 over a lifetime of exposure) and can in general be used for most pharmaceuticals 
as a default to derive an acceptable limit for control. This approach would usually be used for 
mutagenic impurities present in pharmaceuticals for long-term treatment (greater than 10 
years) and where no carcinogenicity data are available (Classes 2 and 3). 
 
B.  Acceptable Intakes Based on Compound-Specific Risk Assessments (7.2) 
 
1.  Mutagenic Impurities With Positive Carcinogenicity Data (Class 1 in Table 1) 
(7.2.1) 
 
Compound-specific risk assessments to derive acceptable intakes should be applied instead of 
the TTC-based acceptable intakes where sufficient carcinogenicity data exist. For a known 
mutagenic carcinogen, a compound-specific acceptable intake can be calculated based on 
carcinogenic potency and linear extrapolation as a default approach. Alternatively, other 
established risk assessment practices such as those used by international regulatory bodies 
may be applied either to calculate acceptable intakes or to use already existing values 
published by regulatory authorities (Note 4). 
 
Compound-specific calculations for acceptable intakes can be applied case by case for 
impurities, which are chemically similar to a known carcinogen compound class (class-
specific acceptable intakes) provided that a rationale for chemical similarity and supporting 
data can be demonstrated (Note 5). 
 
2.  Mutagenic Impurities with Evidence for a Practical Threshold (7.2.2) 
 
The existence of mechanisms leading to a dose response that is nonlinear or has a practical 
threshold is increasingly recognized, not only for compounds that interact with non-DNA 
targets but also for DNA-reactive compounds, whose effects may be modulated by, for 
example, rapid detoxification before coming into contact with DNA, or by effective repair of 
induced damage. The regulatory approach to such compounds can be based on the 
identification of a no observed effect level (NOEL) and use of uncertainty factors (ICH 
guidance for industry Q3C(R8) Impurities: Guidance for Residual Solvents (December 2021), 
Ref. 7) to calculate a permissible daily exposure (PDE) when data are available. 
 
The acceptable intakes derived from compound-specific risk assessments (section VII.B 
(7.2)) can be adjusted for shorter duration of use in the same proportions as defined in the 
following sections (sections VII.C.1 (7.3.1) and VII.C.2 (7.3.2)) or should be limited to not 
more than 0.5 percent, whichever is lower. For example, if the compound-specific acceptable 
intake is 15 g/day for lifetime exposure, the less-than-lifetime limits (Table 2) can be 
9  Contains Nonbinding Recommendations 
increased to a daily intake of 100 g (greater than 1 to 10 years treatment duration), 200 g 
(greater than 1 to 12 months) or 1,200 g (less than 1 month). However, for a drug with a 
maximum daily dose of, for instance, 100 milligrams (mg) the acceptable daily intake for the 
less than 1 months duration would be limited to 0.5 percent (500 g) rather than 1,200 g. 
 
C.  Acceptable Intakes in Relation to LTL Exposure (7.3) 
 
Standard risk assessments of known carcinogens assume that cancer risk increases as a 
function of cumulative dose. Thus, cancer risk of a continuous low dose over a lifetime 
would be equivalent to the cancer risk associated with an identical cumulative exposure 
averaged over a shorter duration. 
 
The TTC-based acceptable intake of 1.5 g/day is considered to be protective for a lifetime of 
daily exposure. To address LTL exposures to mutagenic impurities in pharmaceuticals, an 
approach is applied in which the acceptable cumulative lifetime dose (1.5 g/day times 
25,550 days equals 38.3 mg) is uniformly distributed over the total number of exposure days 
during LTL exposure. This would allow higher daily intake of mutagenic impurities than 
would be the case for lifetime exposure and still maintain comparable risk levels for daily and 
nondaily treatment regimens. Table 2 is derived from the above concepts and illustrates the 
acceptable intakes for LTL to lifetime exposures for clinical development and marketing. In 
the case of intermittent dosing, the acceptable daily intake should be based on the total 
number of dosing days instead of the time interval over which the doses were administered 
and that number of dosing days should be related to the relevant duration category in Table 2. 
For example, a drug administered once per week for 2 years (i.e., 104 dosing days) would 
have an acceptable intake per dose of 20g. 
 
Table 2: Acceptable Intakes for an Individual Impurity 
 
Duration of  < 1  >1 to 12  >1 to 10  >10 Years to 
Treatment  Month  Months  Years  Lifetime 
Daily intake 
120  20  10  1.5 
[g/day] 
 
1.  Clinical Development (7.3.1) 
 
Using this LTL concept, acceptable intakes of mutagenic impurities are recommended for 
limited treatment periods during clinical development of up to 1 month, 1 to 12 months, and 
more than 1 year up to completion of phase 3 clinical trials (Table 2). These adjusted 
acceptable intake values maintain a 10-6 (1 in 1 million) risk level in early clinical 
development when benefit has not yet been established and a 10-5 risk level for later stages in 
development (Note 6). 
 
An alternative approach to the strict use of an adjusted acceptable intake for any mutagenic 
impurity could be applied for phase 1 clinical trials for dosing up to 14 days. For this 
approach, only impurities that are known mutagenic carcinogens (Class 1) and known 
mutagens of unknown carcinogenic potential (Class 2), as well as impurities in the cohort of 
concern chemical class, should be controlled (see section VIII (8)) to acceptable limits as 
described in section VII (7). All other impurities would be treated as nonmutagenic 
10  Contains Nonbinding Recommendations 
impurities. This includes impurities that contain structural alerts (Class 3), which alone would 
not trigger action for an assessment for this limited phase 1 duration. 
 
2.  Marketed Products (7.3.2) 
 
The treatment duration categories with acceptable intakes in Table 2 for marketed products 
are intended to be applied to anticipated exposure durations for the great majority of patients. 
The proposed intakes along with various scenarios for applying those intakes are described in 
Table 4, Note 7. In some cases, a subset of the population of patients may extend treatment 
beyond the marketed drugs categorical upper limit (e.g., treatment exceeding 10 years for an 
acceptable intake of 10 g/day, perhaps receiving 15 years of treatment). This would result in 
a negligible increase (in the example given, a fractional increase to 1.5/100,000) compared to 
the overall calculated risk for the majority of patients treated for 10 years. 
 
D.  Acceptable Intakes for Multiple Mutagenic Impurities (7.4) 
 
The TTC-based acceptable intakes should be applied to each individual impurity. When there 
are two Class 2 or Class 3 impurities, individual limits apply. When there are three or more 
Class 2 or Class 3 impurities specified on the drug substance specification, total mutagenic 
impurities should be limited as described in Table 3 for clinical development and marketed 
products. 
 
For combination products each active ingredient should be regulated separately. 
 
Table 3: Acceptable Total Daily Intakes for Multiple Impurities 
 
         
Duration of  < 1 month  >1 to 12 months  >1 to 10 Years  >10 Years to 
treatment  Lifetime 
Total daily         
intake  120  60  30  5 
[g/day] 
 
Only specified Class 2 and Class 3 impurities on the drug substance specification are 
included in the calculation of the total limit. However, impurities with compound-specific or 
class-related acceptable intake limits (Class 1) should not be included in the total limits of 
Class 2 and Class 3 impurities. Also, degradation products, which form in the drug product, 
would be controlled individually, and a total limit would not be applied. 
 
E.  Exceptions and Flexibility in Approaches (7.5) 
 
  Higher acceptable intakes may be justified when human exposure to the impurity will 
be much greater from other sources, e.g., food, endogenous metabolism (e.g., 
formaldehyde). 
 
  Case-by-case exceptions to the use of the appropriate acceptable intake can be 
justified in cases of severe disease, reduced life expectancy, late onset but chronic 
disease, or with limited therapeutic alternatives. 
11  Contains Nonbinding Recommendations 
 
  Compounds from some structural classes of mutagens can display extremely high 
carcinogenic potency (cohort of concern) (i.e., aflatoxin-like-, N-nitroso-, and alkyl- 
azoxy structures). If these compounds are found as impurities in pharmaceuticals, 
acceptable intakes for these high-potency carcinogens would likely be significantly 
lower than the acceptable intakes defined in this guidance. Although the principles of 
this guidance can be used, a case-by-case approach using, for example, 
carcinogenicity data from closely related structures, if available, should usually be 
developed to justify acceptable intakes for pharmaceutical development and marketed 
products. 
 
The above risk approaches described in section VII (7) are applicable to all routes of 
administration, and no corrections to acceptable intakes are generally warranted. Exceptions 
to consider may include situations where data justify route-specific concerns that should be 
evaluated case by case. These approaches are also applicable to all subject populations based 
upon the conservative nature of the risk approaches being applied. 
 
 
VIII.  CONTROL (8) 
 
A control strategy is a planned set of controls, derived from current product and process 
understanding that assures process performance and product quality (ICH guidance for 
industry Q10 Pharmaceutical Quality System (ICH Q10) (April 2009), Ref. 8). A control 
strategy can include, but is not limited to, the following: 
 
  Controls on material attributes (including raw materials, starting materials, 
intermediates, reagents, solvents, primary packaging materials); 
 
  Facility and equipment operating conditions; 
 
 
  Controls implicit in the design of the manufacturing process; 
 
 
  In-process controls (including in-process tests and process parameters); and 
 
 
  Controls on drug substance and drug product (e.g., release testing). 
 
 
When an impurity has been characterized as Class 1, 2, or 3 in Table 1, it is important to 
develop a control strategy that assures that the level of this impurity in the drug substance and 
drug product is below the acceptable limit. A thorough knowledge of the chemistry 
associated with the drug substance manufacturing process, and of the drug product 
manufacturing process, along with an understanding of the overall stability of the drug 
substance and drug product is fundamental to developing the appropriate controls. 
Developing a strategy to control mutagenic impurities in the drug product is consistent with 
risk management processes identified in the ICH guidance for industry Q9(R1) Quality Risk 
Management (May 2023) (Ref. 9). A control strategy that is based on product and process 
understanding and utilization of risk management principles will lead to a combination of 
12  Contains Nonbinding Recommendations 
process design and control and appropriate analytical testing, which can also provide an 
opportunity to shift controls upstream and minimize the need for end-product testing. 
 
A.  Control of Process-Related Impurities (8.1) 
 
There are four potential approaches to development of a control strategy for a drug substance: 
 
Option 1 
 
Include a test for the impurity in the drug substance specification with an acceptance criterion 
at or below the acceptable limit using an appropriate analytical procedure. 
 
For an Option 1 control approach, it is possible to apply periodic verification testing per the 
ICH guidance for industry Q6A Specifications: Test Procedures and Acceptance Criteria for 
New Drug Substances and New Drug Products: Chemical Substances (ICH Q6A) (December 
2000) (Ref. 10). Periodic verification testing is justified when it can be shown that levels of 
the mutagenic impurity in the drug substance are less than 30 percent of the acceptable limit 
for at least six consecutive pilot scale or three consecutive production scale batches. If this 
condition is not fulfilled, a routine test in the drug substance specification is recommended.  
See section VIII.C (8.3) for additional considerations. 
 
Option 2 
 
Include a test for the impurity in the specification for a raw material, starting material, or 
intermediate, or as an in-process control, with an acceptance criterion at or below the 
acceptable limit using an appropriate analytical procedure. 
 
Option 3 
 
Include a test for the impurity in the specification for a raw material, starting material, or 
intermediate, or as an in-process control, with an acceptance criterion above the acceptable 
limit of the impurity in the drug substance, using an appropriate analytical procedure coupled 
with demonstrated understanding of fate and purge and associated process controls that 
assure the level in the drug substance is below the acceptable limit without the need for any 
additional testing later in the process. 
 
This option can be justified when the level of the impurity in the drug substance will be less 
than 30 percent of the acceptable limit by review of data from laboratory scale experiments 
(spiking experiments are encouraged) and where necessary supported by data from pilot scale 
or commercial scale batches. See case examples 1 and 2 in Appendix 2. Alternative 
approaches can be used to justify Option 3. 
 
Option 4 
 
Understand process parameters and impact on residual impurity levels (including fate and 
purge knowledge) with sufficient confidence that the level of the impurity in the drug 
substance will be below the acceptable limit such that no analytical testing is recommended 
for this impurity (i.e., the impurity does not need to be listed on any specification). 
 
13  Contains Nonbinding Recommendations 
A control strategy that relies on process controls in lieu of analytical testing can be 
appropriate if the process chemistry and process parameters that impact levels of mutagenic 
impurities are understood and the risk of an impurity residing in the final drug substance 
above the acceptable limit is determined to be negligible. In many cases justification of this 
control approach based on scientific principles alone is sufficient. Elements of a scientific 
risk assessment can be used to justify an Option 4 approach. The risk assessment can be 
based on physicochemical properties and process factors that influence the fate and purge of 
an impurity including chemical reactivity, solubility, volatility, Ionizability, and any physical 
process steps designed to remove impurities. The result of this risk assessment might be 
shown as an estimated purge factor for clearance of the impurity by the process (Ref. 11). 
 
Option 4 is especially useful for those impurities that are inherently unstable (e.g., thionyl 
chloride that reacts rapidly and completely with water) or for those impurities that are 
introduced early in the synthesis and are effectively purged. 
 
In some cases an Option 4 approach can be appropriate when the impurity is known to form, 
or is introduced late in the synthesis; however, process-specific data should then be provided 
to justify this approach. 
 
B.  Considerations for Control Approaches (8.2) 
 
For Option 4 approaches where justification based on scientific principles alone is not 
considered sufficient, as well as for Option 3 approaches, analytical data to support the 
control approach is expected. This could include, as appropriate, information on the structural 
changes to the impurity caused by downstream chemistry (fate), analytical data on pilot scale 
batches and, in some cases, laboratory scale studies with intentional addition of the impurity 
(spiking studies). In these cases, it is important to demonstrate that the fate/purge argument 
for the impurity is robust and will consistently assure a negligible probability of an impurity 
residing in the final drug substance above the acceptable limit. Where the purge factor is 
based on developmental data, it is important to address the expected scale dependence or 
independence. In the case that the small scale model used in the development stage is 
considered to not represent the commercial scale, confirmation of suitable control in pilot 
scale and/or initial commercial batches is generally appropriate. The need for data from 
pilot/commercial batches is influenced by the magnitude of the purge factor calculated from 
laboratory or pilot scale data, point of entry of the impurity, and knowledge of downstream 
process purge points. 
 
If Options 3 and 4 cannot be justified, then a test for the impurity on the specification for a 
raw material, starting material or intermediate, or as an in-process control (Option 2) or drug 
substance (Option 1) at the acceptable limit should be included. For impurities introduced in 
the last synthetic step, an Option 1 control approach would be expected unless otherwise 
justified. 
 
The application of as low as reasonably practicable (ALARP) is not necessary if the level of 
the mutagenic impurity is below acceptable limits. Similarly, it is not necessary to 
demonstrate that alternate routes of synthesis have been explored. 
 
In cases where control efforts cannot reduce the level of the mutagenic impurity to below the 
acceptable limit and levels are ALARP, a higher limit may be justified based on a benefit-risk 
analysis. 
14  Contains Nonbinding Recommendations 
 
C.  Considerations for Periodic Testing (8.3) 
 
The above options include situations where a test is recommended to be included in the 
specification, but where routine measurement for release of every batch may not be 
necessary. This approach, referred to as periodic or skip testing in ICH Q6A could also be 
called periodic verification testing. This approach may be appropriate when it can be 
demonstrated that processing subsequent to impurity formation/introduction clears the 
impurity. It should be noted that allowance of periodic verification testing is contingent upon 
use of a process that is under a state of control (i.e., produces a quality product that 
consistently meets specifications and conforms to an appropriately established facility, 
equipment, processing, and operational control regimen). If upon testing, the level of the 
mutagenic impurity fails to meet the acceptance criteria established for the periodic test, the 
drug producer should immediately commence full testing (i.e., testing of every batch for the 
attribute specified) until the cause of the failure has been conclusively determined, corrective 
action has been implemented, and the process is again documented to be in a state of control. 
As noted in ICH Q6A, regulatory authorities should be notified of a periodic verification test 
failure to evaluate the benefit/risk of previously released batches that were not tested. 
 
D.  Control of Degradation Products (8.4) 
 
For a potential degradation product that has been characterized as mutagenic, it is important 
to understand if the degradation pathway is relevant to the drug substance and drug product 
manufacturing processes and/or their proposed packaging and storage conditions. A well- 
designed accelerated stability study (e.g., 40C/75 percent relative humidity, 6 months) in the 
proposed packaging, with appropriate analytical procedures is recommended to determine the 
relevance of the potential degradation product. Alternatively, well-designed, kinetically 
equivalent shorter term stability studies at higher temperatures in the proposed commercial 
package may be used to determine the relevance of the degradation pathway before initiating 
longer term stability studies. This type of study would be especially useful to understand the 
relevance of those potential degradation products that are based on knowledge of potential 
degradation pathways but not yet observed in the product. 
 
Based on the result of these accelerated studies, if it is anticipated that the degradation 
product will form at levels approaching the acceptable limit under the proposed packaging 
and storage conditions, then efforts to control formation of the degradation product is 
expected. In these cases, monitoring for the drug substance or drug product degradation 
product in long-term primary stability studies at the proposed storage conditions (in the 
proposed commercial pack) is expected unless otherwise justified. Whether or not a 
specification limit for the mutagenic degradation product is appropriate will generally depend 
on the results from these stability studies. 
 
If it is anticipated that formulation development and packaging design options are unable to 
control mutagenic degradation product levels to less than the acceptable limit and levels are 
ALARP, a higher limit can be justified based on a benefit-risk analysis. 
 
E.  Lifecycle Management (8.5) 
 
This section is intended to apply to those products approved after the issuance of this 
guidance. 
15  Contains Nonbinding Recommendations 
 
The quality system elements and management responsibilities described in ICH Q10 are 
intended to encourage the use of science-based and risk-based approaches at each lifecycle 
stage, thereby promoting continual improvement across the entire product lifecycle. Product 
and process knowledge should be managed from development through the commercial life of 
the product up to and including product discontinuation. 
 
The development and improvement of a drug substance or drug product manufacturing 
process usually continues over its lifecycle. Manufacturing process performance, including 
the effectiveness of the control strategy, should be periodically evaluated. Knowledge gained 
from commercial manufacturing can be used to further improve process understanding and 
process performance and to adjust the control strategy. 
 
Any proposed change to the manufacturing process should be evaluated for the impact on the 
quality of drug substance and drug product. This evaluation should be based on 
understanding of the manufacturing process and should determine if appropriate testing to 
analyze the impact of the proposed changes is required. Additionally, improvements in 
analytical procedures may lead to structural identification of an impurity. In those cases the 
new structure would be assessed for mutagenicity as described in this guidance. 
 
Throughout the lifecycle of the product, it will be important to reassess if testing is 
recommended when intended or unintended changes occur in the process. This applies when 
there is no routine monitoring at the acceptable limit (Option 3 or Option 4 control 
approaches) or when applying periodic rather than batch-by-batch testing. This testing should 
be performed at an appropriate point in the manufacturing process. 
 
In some cases, the use of statistical process control and trending of process measurements can 
be useful for continued suitability and capability of processes to provide adequate control on 
the impurity. Statistical process control can be based on process parameters that influence 
impurity formation or clearance, even when that impurity is not routinely monitored (e.g., 
Option 4). 
 
All changes should be subject to internal change management processes as part of the quality 
system (ICH Q10). Changes to information filed and approved in a dossier should be reported 
to regulatory authorities in accordance with regional regulations and guidances. 
 
F.  Considerations for Clinical Development (8.6) 
 
It is recognized that product and process knowledge increases over the course of 
development, and therefore, it is expected that data to support control strategies in the clinical 
development trial phases will be less than at the marketing registration phase. A risk-based 
approach based on process chemistry fundamentals is encouraged to prioritize analytical 
efforts on those impurities with the highest likelihood of being present in the drug substance 
or drug product. Analytical data may not be expected to support early clinical development 
when the likelihood of an impurity being present is low, but in a similar situation analytical 
data may be appropriate to support the control approach for the marketing application. It is 
also recognized that commercial formulation design occurs later in clinical development and 
therefore efforts associated with drug product degradation products will be limited in the 
earlier phases. 
 
16  Contains Nonbinding Recommendations 
 
IX.  DOCUMENTATION (9) 
 
Information relevant to the application of this guidance should be provided at the following 
stages: 
 
A.  Clinical Trial Applications (9.1) 
 
  It is expected that the number of structures assessed for mutagenicity and the 
collection of analytical data will both increase throughout the clinical development 
period. 
 
  For phase 1 studies of 14 days or less, a description of efforts to mitigate risks of 
mutagenic impurities focused on Class 1 and Class 2 impurities and those in the 
cohort of concern as outlined in section VII (7) should be included. For phase 1 
clinical trials greater than 14 days and for phase 2a clinical trials additionally Class 3 
impurities that require analytical controls should be included. 
 
  For phase 2b and phase 3 clinical development trials, a list of the impurities assessed 
by (Q)SAR should be included, and any Class 1, Class 2, or Class 3 actual and 
potential impurities should be described along with plans for control. The in silico 
(Q)SAR systems used to perform the assessments should be described. The results of 
bacterial mutagenicity tests of actual impurities should be reported. 
 
  Chemistry arguments may be appropriate instead of analytical data for potential 
impurities that present a low likelihood of being present as described in section VIII. 
F (8.6). 
 
B.  Common Technical Document (Marketing Application) (9.2) 
 
  For actual and potential process-related impurities and degradation products where 
assessments according to this guidance are conducted, the mutagenic impurity 
classification and rationale for this classification should be provided: 
 
 This would include the results and description of in silico (Q)SAR systems used 
and, as appropriate, supporting information to arrive at the overall conclusion for 
Class 4 and Class 5 impurities. 
 
 When bacterial mutagenicity assays were performed on impurities, study reports 
should be provided for bacterial mutagenicity assays on impurities. 
 
  Justification for the proposed specification and the approach to control should be 
provided (e.g., the ICH guidance for industry Q11 Development and Manufacture of 
Drug Substances (Chemical Entities and Biotechnological/Biological Entities) 
(November 2012) example Table 5b at 2930, Ref. 12). For example, this information 
could include the acceptable intake, the location, and sensitivity of relevant routine 
monitoring. For Option 3 and Option 4 control approaches, a summary of knowledge 
of the purge factor and identification of factors providing control (e.g., process steps, 
solubility in wash solutions) is important. 
 
17  Contains Nonbinding Recommendations 
NOTES 
 
Note 1 The International Council for Harmonisation (ICH) guidance for industry M7(R2) 
Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals 
to Limit Potential Carcinogenic Risk (ICH M7(R2)) recommendations provide a state-
of-the-art approach for assessing the potential of impurities to induce point mutations 
and ensure that such impurities are controlled to safe levels so that below or above the 
ICH Q3A and Q3B(R2) qualification threshold no further qualification for mutagenic 
potential is required. This includes the initial use of (quantitative) structure-activity 
relationship ((Q)SAR) tools to predict bacterial mutagenicity. In cases where the 
amount of the impurity exceeds 1 milligram (mg) daily dose for chronic 
administration, evaluation of genotoxic potential as recommended in ICH 
Q3A/Q3B(R2) could be considered. In cases where the amount of the impurity is 
equal to or less than 1 mg, no further genotoxicity testing is required regardless of 
other qualification thresholds. 
 
Note 2 To assess the mutagenic potential of impurities, a single bacterial mutagenicity assay 
can be carried out with a fully adequate protocol according to the ICH guidance for 
industry S2(R1) Genotoxicity Testing and Data Interpretation for Pharmaceuticals 
Intended for Human Use (June 2012) and OECD Test 471 guideline (Ref. 13, 14). 
The assays are expected to be performed in compliance with good laboratory practice 
(GLP) regulations; however, lack of full GLP compliance does not necessarily mean 
that the data cannot be used to support clinical trials and marketing authorizations. 
Such deviations should be described in the study report. For example, the test article 
may not be prepared or analyzed in compliance with GLP regulations. In some cases, 
the selection of bacterial tester strains may be limited to those proven to be sensitive 
to the identified alert. For impurities that are not feasible to isolate or synthesize or 
when compound quantity is limited, it may not be possible to achieve the highest test 
concentrations recommended for an ICH-compliant bacterial mutagenicity assay 
according to the current testing guidelines. In this case, bacterial mutagenicity testing 
could be carried out using a miniaturized assay format with proven high concordance 
to the ICH-compliant assay to enable testing at higher concentrations with 
justification. 
 
Note 3 Tests to Investigate the In Vivo Relevance of In Vitro Mutagens (Positive 
Bacterial Mutagenicity) 
 
Factors to Justify Choice  
In Vivo Test 
of Test as Fit-for-Purpose 
Transgenic mutation assays 
  For any bacterial mutagenicity positive. Justify selection 
of assay tissue/organ 
Pig-a assay    For directly acting mutagens (bacterial mutagenicity 
(blood)  positive without S9)* 
Micronucleus test    For directly acting mutagens (bacterial mutagenicity 
(blood or bone marrow)  positive without S9) and compounds known to be 
clastogenic* 
18  Contains Nonbinding Recommendations 
Factors to Justify Choice  
In Vivo Test 
of Test as Fit-for-Purpose 
Rat liver unscheduled DNA    In particular for bacterial mutagenicity positive with S9 
synthesis (UDS) test  only 
  Responsible liver metabolite known 
 To be generated in test species used 
 To induce bulky adducts 
Comet assay    Justification needed (chemical class-specific mode of 
action to form alkaline labile sites or single-strand 
breaks as preceding DNA damage that can potentially 
lead to mutations) 
  Justify selection of assay tissue/organ 
Others    With convincing justification 
* For  indirect acting mutagens (requiring metabolic activation), adequate exposure to metabolite(s) should 
be demonstrated. 
 
Note 4 Example of linear extrapolation from the TD  
50
 
It is possible to calculate a compound-specific acceptable intake based on rodent 
carcinogenicity potency data such as TD  values (doses giving a 50 percent tumor 
50
incidence equivalent to a cancer risk probability level of 1:2). Linear extrapolation to 
a probability of 1 in 100,000 (i.e., the accepted lifetime risk level used) is achieved by 
simply dividing the TD  by 50,000. This procedure is similar to that employed for 
50
derivation of the TTC. 
 
Calculation example: Ethylene oxide 
 
TD  values for ethylene oxide according to the Carcinogenic Potency Database are 
50
21.3 mg/kilogram (kg) body weight/day (rat) and 63.7 mg/kg body weight/day 
(mouse). For the calculation of an acceptable intake, the lower (i.e., more 
conservative) value of the rat is used. 
 
To derive a dose to cause tumors in 1 in 100,000 animals, divide by 50,000:  
 
21.3 mg/kg  50,000 = 0.42 g/kg 
 
To derive a total human daily dose: 
 
0.42 g/kg/day x 50 kg body weight = 21.3 g/person/day 
 
Hence, a daily lifelong intake of 21.3 g ethylene oxide would correspond to a 
theoretical cancer risk of 10-5 and therefore be an acceptable intake when present as 
an impurity in a drug substance.  
 
Alternative methods and published regulatory limits for cancer risk assessment 
 
As an alternative of using the most conservative TD  value from rodent 
50
carcinogenicity studies irrespective of its relevance to humans, an in-depth 
19  Contains Nonbinding Recommendations 
toxicological expert assessment of the available carcinogenicity data can be done to 
initially identify the findings (species, organ, etc.) with highest relevance to human 
risk assessment as a basis for deriving a reference point for linear extrapolation. Also, 
to better take into account directly the shape of the dose-response curve, a benchmark 
dose such as a benchmark dose lower confidence limit 10 percent (BMDL10, an 
estimate of the lowest dose which is 95 percent certain to cause no more than a 10 
percent cancer incidence in rodents) may be used instead of TD  values as a 
50
numerical index for carcinogenic potency. Linear extrapolation to a probability of 1 in 
100,000 (i.e., the accepted lifetime risk level used) is then achieved by simply 
dividing the BMDL10 by 10,000. 
 
Compound-specific acceptable intakes can also be derived from published 
recommended values from internationally recognized bodies such as the World Health 
Organization (WHO, International Programme on Chemical Safety (IPCS) Cancer 
Risk Assessment Programme) and others using the appropriate 10-5 lifetime risk 
level. In general, a regulatory limit that is applied should be based on the most current 
and scientifically supported data and/or methodology. 
 
Note 5 A compound-specific calculation of acceptable intakes for mutagenic impurities may 
be applied for mutagenic impurities (without carcinogenicity data), which are 
structurally similar to a chemically defined class of known carcinogen. For example, 
factors that are associated with the carcinogenic potency of monofunctional alkyl 
chlorides have been identified (Ref. 15) and can be used to modify the safe acceptable 
intake of monofunctional alkyl chlorides, a group of alkyl chlorides commonly used 
in drug synthesis. Compared to multifunctional alkyl chlorides the monofunctional 
compounds are much less potent carcinogens with TD  values ranging from 36 to 
50
1810 mg/kg/day (n=15; epichlorohydrin with two distinctly different functional 
groups is excluded). A TD  value of 36 mg/kg/day can thus be used as a still very 
50
conservative class-specific potency reference point for calculation of acceptable 
intakes for monofunctional alkyl chlorides. This potency level is at least tenfold lower 
than the TD  of 1.25 mg/kg/day corresponding to the default lifetime TTC (1.5 
50
g/day) and therefore justifies lifetime and LTL daily intakes for monofunctional 
alkyl chlorides 10 times the default ones. 
 
Note 6 Establishing LTL acceptable intakes for mutagenic impurities in pharmaceuticals has 
precedent in the establishment of the staged TTC limits for clinical development (Ref. 
16). The calculation of LTL acceptable intakes (AI) is predicated on the principle of 
Habers rule, a fundamental concept in toxicology where concentration (C) multiplied 
by time (T) equals a constant (k). Therefore, the carcinogenic effect is based on both 
dose and duration of exposure. 
 
20  Contains Nonbinding Recommendations 
 
 
Figure 1: Illustration of calculated daily dose of a mutagenic impurity corresponding 
to a theoretical 1:100,000 cancer risk as a function of duration of treatment in 
comparison to the acceptable intake levels as recommended in section VII.C (7.3). 
 
The solid line in Figure 1 represents the linear relationship between the amount of 
daily intake of a mutagenic impurity corresponding to a 10-5 cancer risk and the 
number of treatment days. The calculation is based on the TTC level as applied in this 
guidance for lifelong treatment, i.e., 1.5 g per person per day using the formula: 
 
Less-than-lifetime AI = 1.5 g x (365 days x 70 years lifetime = 25,550) 
Total number of treatment days 
 
The calculated daily intake levels would thus be 1.5 g for treatment duration of 70 
years, 10 g for 10 years, 100 g for 1 year, 1270 g for 1 month, and approximately 
38.3 mg as a single dose, all resulting in the same cumulative intake and therefore 
theoretically in the same cancer risk (1 in 100,000). 
 
The dashed step-shaped curve represents the actual daily intake levels adjusted to 
less-than-lifetime exposure as recommended in section VII (7) of this guidance for 
products in clinical development and marketed products. These proposed levels are in 
general significantly lower than the calculated values thus providing safety factors 
that increase with shorter treatment durations. 
 
The proposed accepted daily intakes are also in compliance with a 10-6 cancer risk 
level if treatment durations are not longer than 6 months and are therefore applicable 
in early clinical trials with volunteers/subjects where benefit has not yet been 
established. In this case the safety factors as shown in the upper graph would be 
reduced by a factor of 10. 
21  Contains Nonbinding Recommendations 
 
Note 7 Table 4: Examples of Clinical Use Scenarios With Different Treatment 
Durations for Applying Acceptable Intakes 
 
Scenario*  Acceptable Intake 
(g/day) 
Treatment duration of < 1 month: e.g., drugs used in emergency  120 
procedures (antidotes, anesthesia, acute ischemic stroke), actinic 
keratosis, treatment of lice 
Treatment duration of > 112 months: e.g., anti-infective therapy  20 
with maximum up to 12 months treatment (hepatitis C virus), 
parenteral nutrients, prophylactic flu drugs (~5 months), peptic ulcer, 
assisted reproductive technology (ART), preterm labor, preeclampsia, 
presurgical (hysterectomy) treatment, fracture healing (these are acute 
use but with long half-lives) 
Treatment duration of >110 years: e.g., stage of disease with short  10 
life expectancy (severe Alzheimers disease), nongenotoxic anticancer 
treatment being used in a patient population with longer term survival 
(breast cancer, chronic myelogenous leukemia), drugs specifically 
labeled for less than 10 years of use, drugs administered intermittently 
to treat acute recurring symptoms** (chronic herpes, gout attacks, 
substance dependence such as smoking cessation), macular 
degeneration 
Treatment duration of >10 years to lifetime: e.g., chronic use  1.5 
indications with high likelihood for lifetime use across broader age 
range (hypertension, dyslipidemia, asthma, Alzheimers disease 
(except severe Alzheimers disease), hormone therapy (e.g., growth 
hormone, thyroid hormone, parathyroid hormone), lipodystrophy, 
schizophrenia, depression, psoriasis, atopic dermatitis, chronic 
obstructive pulmonary disease (COPD), cystic fibrosis, seasonal and 
perennial allergic rhinitis, HIV***) 
* This table shows general examples; each example should be examined on a case-by-case basis.  For 
example, 10 g/day may be acceptable in cases where the life expectancy of the patient may be limited 
(e.g., severe Alzheimers disease) even though the drug use could exceed a 10-year duration. 
** Intermittent use over a period greater than 10 years but based on calculated cumulative dose it falls under 
the greater than 1 to 10 years category. 
*** Changed in this guidance (ICH M7(R2)) from 1 to 10 years to greater than10 years to lifetime because of 
clinical treatment advances.  See the ICH guidance for industry M7(R2) Assessment and Control of DNA 
Reactive (Mutagenic) Impurities in Pharmaceuticals to Limit Potential Carcinogenic Risk: Questions and 
Answers (July 2023). 
 
22  Contains Nonbinding Recommendations 
GLOSSARY 
 
Acceptable intake: 
 
In the context of this guidance, an intake level that poses negligible cancer risk, or for 
serious/life-threatening indications where risk and benefit are appropriately balanced. 
 
Acceptable limit: 
 
Maximum acceptable concentration of an impurity in a drug substance or drug product 
derived from the acceptable intake and the daily dose of the drug. 
 
Acceptance criterion: 
 
Numerical limits, ranges, or other suitable measures for acceptance of the results of analytical 
procedures. 
 
Control strategy: 
 
A planned set of controls, derived from current product and process understanding that 
ensures process performance and product quality. The controls can include parameters and 
attributes related to drug substance and drug product materials and components, facility and 
equipment operating conditions, in-process controls, finished product specifications, and the 
associated methods and frequency of monitoring and control. 
 
Cumulative intake: 
 
The total intake of a substance that a person is exposed to over time. 
 
Degradation product:  
 
A molecule resulting from a chemical change in the drug molecule brought about over time 
and/or by the action of light, temperature, pH, or water or by reaction with an excipient 
and/or the immediate container/closure system. 
 
DNA-reactive: 
 
The potential to induce direct DNA damage through chemical reaction with DNA. 
 
Expert knowledge: 
 
In the context of this guidance, expert knowledge can be defined as a review of preexisting 
data and the use of any other relevant information to evaluate the accuracy of an in silico 
model prediction for mutagenicity. 
 
Genotoxicity: 
 
A broad term that refers to any deleterious change in the genetic material regardless of the 
mechanism by which the change is induced. 
 
23  Contains Nonbinding Recommendations 
Impurity: 
 
Any component of the drug substance or drug product that is not the drug substance or an 
excipient. 
 
Mutagenic impurity: 
 
An impurity that has been demonstrated to be mutagenic in an appropriate mutagenicity test 
model (e.g., bacterial mutagenicity assay). 
 
Periodic verification testing: 
 
Also known as periodic or skip testing in the International Council for Harmonisation 
guidance for industry Q6A Specifications: Test Procedures and Acceptance Criteria for New 
Drug Substances and New Drug Products: Chemical Substances (December 2000).1 
 
(Q)SAR and SAR: 
 
In the context of this guidance, refers to the relationship between the molecular (sub) 
structure of a compound and its mutagenic activity using (quantitative) structure-activity 
relationships derived from experimental data. 
 
Purge factor: 
 
Purge reflects the ability of a process to reduce the level of an impurity, and the purge factor 
is defined as the level of an impurity at an upstream point in a process divided by the level of 
an impurity at a downstream point in a process. Purge factors may be measured or predicted. 
 
Structural alert: 
 
In the context of this guidance, a chemical grouping or molecular (sub) structure, which is 
associated with mutagenicity. 
 
 
1 We update guidances periodically. To make sure you have the most recent version of a guidance, check the 
FDA guidance web page at https://www.fda.gov/regulatory-information/search-fda-guidance-documents.  
24  Contains Nonbinding Recommendations 
REFERENCES 
 
1.  International Council for Harmonisation (ICH) guidance for industry Q3A Impurities 
in New Drug Substances (Revision 2) (June 2008)1 
 
2.  ICH guidance for industry Q3B(R2) Impurities in New Drug Products (August 2006) 
 
3.  ICH guidance for industry M3(R2) Nonclinical Safety Studies for the Conduct of 
Human Clinical Trials and Marketing Authorization for Pharmaceuticals (January 
2010) 
 
4.  ICH guidance for industry S9 Nonclinical Evaluation for Anticancer Pharmaceuticals 
(March 2010) 
 
5.  ICH guidance for industry Q1B Photostability Testing of New Drug Substances and 
Products (November 1996) 
 
6.  Sutter A, Amberg A, Boyer S, Brigo A, Contrera JF, Custer LL, Dobo KL, Gervais V, 
Glowienke S, van Gompel J, Greene N, Muster W, Nicolette J, Reddy MV, Thybaud 
V, Vock E, White AT, and Muller L, 2013, Use of In Silico Systems and Expert 
Knowledge for Structure-Based Assessment of Potentially Mutagenic Impurities, 
Regul Toxicol Pharmacol, 67(1):3952. 
 
7.  ICH guidance for industry Q3C(R8): Impurities: Guidance for Residual Solvents 
(December 2021) 
 
8.  ICH guidance for industry Q10 Pharmaceutical Quality System (April 2009) 
 
9.  ICH guidance for industry Q9(R1) Quality Risk Management (May 2023) 
 
10. ICH guidance for industry Q6A Specifications: Test Procedures and Acceptance 
Criteria for New Drug Substances and New Drug Products: Chemical Substances 
(December 2000) 
 
11. Teasdale A, Elder D, Chang S-J, Wang S, Thompson R, Benz N, and Sanchez Flores 
I, 2013, Risk Assessment of Genotoxic Impurities in New Chemical Entities: 
Strategies to Demonstrate Control, Org Process Res Dev;17:221230. 
 
12. ICH guidance for industry Q11 Development and Manufacture of Drug Substances 
(November 2012) 
 
13. ICH guidance for industry S2(R1) Genotoxicity Testing and Data Interpretation for 
Pharmaceuticals Intended for Human Use (June 2012) 
 
14. Test 471. Bacterial Reverse Mutation Test Organization for Economic Co-operation 
and Development Guideline for Testing of Chemicals Section 4, July 1997, available 
at https://www.oecd.org/chemicalsafety/risk-assessment/1948418.pdf.  
 
1 We update guidances periodically.  To make sure you have the most recent version of a guidance, check the 
FDA guidance web page at https://www.fda.gov/regulatory-information/search-fda-guidance-documents.  
25  Contains Nonbinding Recommendations 
 
15. Brigo A and Muller L, 2011, Development of the Threshold of Toxicological Concern 
Concept and Its Relationship to Duration of Exposure, in Genotoxic Impurities (Ed. 
A. Teasdale), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 
10.1002/9780470929377.ch2 
 
16. Muller L, Mauthe RJ, Riley CM, Andino MM, De Antonis D, Beels C, DeGeorge J, 
De Knaep AGM, Ellison D, Fagerland JA, Frank R, Fritschel B, Galloway S, Harpur 
E, Humfrey CDN, Jacks ASJ, Jagota N, Mackinnon J, Mohan G, Ness DK, 
ODonovan MR, Smith MD, Vudathala G, and Yotti L, 2006, A Rationale for 
Determining, Testing, and Controlling Specific Impurities in Pharmaceuticals That 
Possess Potential for Genotoxicity, Regul Toxicol Pharmacol, 44:198211. 
 
26  Contains Nonbinding Recommendations 
APPENDIX 1: SCOPE SCENARIOS  
FOR APPLICATION OF THE ICH M7(R2) GUIDANCE1 
 
Applies to  Applies 
Scenario  Drug  to Drug  Comments 
Substance  Product 
Registration of new drug  Yes  Yes  Primary intent of the ICH M7(R2) 
substances and associated  guidance. 
drug product. 
Clinical trial applications  Yes  Yes  Primary intent of the ICH M7(R2) 
for new drug substances  guidance. 
and associated drug 
product. 
Clinical trial applications  No  No  Out of scope of the ICH M7(R2) 
for new drug substances  guidance. 
for an anticancer drug 
per the ICH guidance 
for industry S9 
Nonclinical Evaluation 
for Anticancer 
Pharmaceuticals (March 
2010) (ICH S9). 
Clinical trial applications  Yes  Yes  There may be exceptions on a case-
for new drug substances  by-case basis for higher impurity 
for an orphan drug.  limits. 
Clinical trial application  No  Yes  Retrospective application of the ICH 
for a new drug product  M7(R2) guidance is not intended for 
using an existing drug  marketed products unless there are 
substance where there are  changes made to the synthesis. 
no changes to the drug  Because no changes are made to the 
substance manufacturing  drug substance synthesis, the drug 
process.  substance would not require 
reevaluation. Because the drug 
product is new, application of the 
ICH M7(R2) guidance is expected. 
A new formulation of an  No  Yes  See section IV.B (4.2) of the ICH 
approved drug substance  M7(R2) guidance. 
is filed. 
A product that is  Yes  Yes  Because there is no mutual 
previously approved in a  recognition, an existing product in 
member region is filed for  one member region filed for the first 
the first time in a different  time in another member region 
member region. The  would be considered a new product. 
product is unchanged. 
 
1 International Council for Harmonisation (ICH) guidance for industry M7(R2) Assessment and Control of DNA 
Reactive (Mutagenic) Impurities in Pharmaceuticals to Limit Potential Carcinogenic Risk (ICH M7(R2)). 
27  Contains Nonbinding Recommendations 
Applies to  Applies 
Scenario  Drug  to Drug  Comments 
Substance  Product 
A new supplier or new  No  No  As long as the synthesis of the drug 
site of the drug substance  substance is consistent with 
is registered. There are no  previously approved methods, then 
changes to the  reevaluation of mutagenic impurity 
manufacturing process  risk is not necessary. The applicant 
used in this registered  would need to demonstrate that no 
application.  changes have been made to a 
previously approved process/product. 
See section IV.A (4.1) of the ICH 
M7(R2) guidance. 
An existing product  Yes  Yes  Since the patient population and 
(approved after the  acceptable cancer risk have changed, 
issuance of ICH M7(R2)  the previously approved impurity 
with higher limits based  control strategy and limits will warrant 
on ICH S9) associated  reevaluation.  See section IV.C (4.3) of 
with an advanced cancer  ICH M7(R2). 
indication is now 
registered for use in a 
nonlife-threatening 
indication. 
New combination product  Yes (new  Yes  ICH M7(R2) would apply to the new 
is filed that contains one  drug  drug substance. For the existing drug 
new drug substance and  substance)  substance, retrospective application 
an existing drug substance.  No  of ICH M7(R2) to existing products 
(existing  is not intended. For the drug 
drug  product, this would classify as a new 
substance)  drug product so the guidance would 
apply to any new or higher levels of 
degradation products. 
 
28  Contains Nonbinding Recommendations 
APPENDIX 2:  CASE EXAMPLES  
TO ILLUSTRATE POTENTIAL CONTROL APPROACHES 
 
Case 1: Example of an Option 3 Control Strategy 
 
An intermediate X is formed two steps away from the drug substance, and impurity A is 
routinely detected in intermediate X. The impurity A is a stable compound and carries over to 
the drug substance. A spike study of the impurity A at different concentration levels in 
intermediate X was performed at laboratory scale. As a result of these studies, impurity A 
was consistently removed to less than 30 percent of the threshold of toxicological concern 
(TTC) based limit in the drug substance even when impurity A was present at 1 percent in 
intermediate X. Because this intermediate X is formed only two steps away from the drug 
substance and the impurity A level in the intermediate X is relatively high, the purging ability 
of the process has additionally been confirmed by determination of impurity A in the drug 
substance in multiple pilot scale batches and results were below 30 percent of the TTC-based 
limit. Therefore, control of the impurity A in the intermediate X with an acceptance limit of 1  
percent is justified and no test is warranted for this impurity in the drug substance 
specification. 
 
Case 2: Example of an Option 3 Control Strategy: Based on Predicted Purge From a 
Spiking Study Using Standard Analytical Methods 
 
A starting material Y is introduced in step 3 of a five-step synthesis, and an impurity B is 
routinely detected in the starting material Y at less than 0.1 percent using standard analytical 
methods. To determine if the 0.1 percent specification in the starting material is acceptable, a 
purge study was conducted at laboratory scale where impurity B was spiked into starting 
material Y with different concentration levels up to 10 percent and a purge factor of greater 
than 500-fold was determined across the final three processing steps. This purge factor 
applied to a 0.1 percent specification in starting material Y would result in a predicted level 
of impurity B in the drug substance of less than 2 parts per million (ppm). Because this is 
below the TTC-based limit of 50 ppm for this impurity in the drug substance, the 0.1 percent 
specification of impurity B in starting material Y is justified without the need for providing 
drug substance batch data on pilot scale or commercial scale batches. 
 
Case 3: Example of an Option 2 and Option 4 Control Strategy: Control of Structurally 
Similar Mutagenic Impurities 
 
The step 1 intermediate of a five-step synthesis is a nitroaromatic compound that may contain 
low levels of impurity C, a positional isomer of the step 1 intermediate and also a 
nitroaromatic compound. The amount of impurity C in the step 1 intermediate has not been 
detected by ordinary analytical methods, but it may be present at lower levels. The step 1 
intermediate is positive in the bacterial mutagenicity assay. The step 2 hydrogenation reaction 
results in a 99 percent conversion of the step 1 intermediate to the corresponding aromatic 
amine. This is confirmed via in-process testing. An assessment of purge of the remaining step 
1 nitroaromatic intermediate was conducted and a high purge factor was predicted based on 
purge points in the subsequent step 3 and step 4 processing steps. Purge across the step 5 
processing step is not expected and a specification for the step 1 intermediate at the TTC- 
based limit was established at the step 4 intermediate (Option 2 control approach). The 
positional isomer impurity C would be expected to purge via the same purge points as the 
step 1 intermediate and, therefore, will always be much lower than the step 1 intermediate 
29  Contains Nonbinding Recommendations 
itself, and therefore, no testing is required, and an Option 4 control strategy for impurity C 
can be supported without the need for any additional laboratory or pilot scale data. 
 
Case 4: Example of an Option 4 Control Strategy: Highly Reactive Impurity 
 
Thionyl chloride is a highly reactive compound that is mutagenic. This reagent is introduced 
in step 1 of a five-step synthesis. At multiple points in the synthesis, significant amounts of 
water are used. Because thionyl chloride reacts instantaneously with water, there is no chance 
of any residual thionyl chloride to be present in the drug substance. An Option 4 control 
approach is suitable without the need for any laboratory or pilot scale data. 
 
Implementation of Guidance: 
 
Implementation of the International Council for Harmonisation (ICH) guidance for industry 
M7(R2) Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals 
to Limit Potential Carcinogenic Risk (ICH M7(R2)) is encouraged after publication; 
however, because of the complexity of the guidance, application of ICH M7(R2) is not 
expected prior to 18 months after ICH publication. 
 
The following exceptions to the 18-month timeline apply. 
 
1.  Ames tests should be conducted according to ICH M7(R2) upon ICH publication. 
However, Ames tests conducted prior to publication of ICH M7(R2) need not be 
repeated. 
 
2.  When development programs have started phase 2b/3 clinical trials prior to 
publication of ICH M7(R2) these programs can be completed up to and including 
marketing application submission and approval, with the following exceptions to ICH 
M7(R2). 
 
 No need for two (quantitative) structure-activity relationship assessments as 
outlined in section VI (6) of ICH M7(R2). 
 
 No need to comply with the scope of product impurity assessment as outlined in 
section V (5) of ICH M7(R2). 
 
 No need to comply with the documentation recommendations as outlined in 
section IX (9) of ICH M7(R2). 
 
3.  Given the similar challenges for development of a commercial manufacturing process, 
application of the aspects of ICH M7(R2) listed above to new marketing applications 
that do not include phase 2b/3 clinical trials would not be expected until 36 months 
after ICH publication of ICH M7(R2). 
 
30  Contains Nonbinding Recommendations 
APPENDIX 3: LIST OF COMPOUNDS IN ICH M7(R2) ADDENDUM:1 
ACCEPTABLE INTAKES OR PERMISSIBLE DAILY EXPOSURES  
 
Compound  CAS#  Chemical  AI  or  PDE  Comment 
Structure  (g/day) 
Linear Extrapolation From TD
50 
Acrylonitrile  107-13-1    6  TD50 linear 
extrapolation 
Benzyl chloride  100-44-7    41  TD50 linear 
extrapolation 
Bis(chloromethyl)ether  542-88-1    0.004  TD50 linear 
extrapolation 
1-Chloro-4-  100-00-5    117  TD50 linear 
nitrobenzene  extrapolation 
p-Cresidine  120-71-8    45  TD50 linear 
extrapolation 
1,2-Dibromoethane  106-93-4    2  TD50 linear 
extrapolation 
Dimethylcarbamyl  79-44-7    0.6 (inhalation)*  TD50 linear 
chloride  5 (all other  extrapolation 
routes) 
 
Epichlorohydrin  106-89-8    3  TD50 linear 
extrapolation 
Ethyl bromide  74-96-4    32  TD50 linear 
extrapolation 
Ethyl chloride  75-00-3    1,810  TD50 linear 
extrapolation 
Glycidol  556-52-5    4  TD50 linear 
extrapolation 
Hydrazine  302-01-2    0.2 (inhalation)*  TD50 linear 
extrapolation 
39 (all other 
routes) 
Methyl Chloride  74-87-3     1,361  TD50 linear 
extrapolation 
 
1 See the International Council for Harmonisation guidance for industry M7(R2) Addendum: Application of the 
Principles of the ICH M7 Guidance to Calculation of Compound-Specific Acceptable Intakes (July 2023).  We 
update guidances periodically.  To make sure you have the most recent version of a guidance, check the FDA 
guidance web page at https://www.fda.gov/regulatory-information/search-fda-guidance-documents.  
31  Contains Nonbinding Recommendations 
Compound  CAS#  Chemical  AI  or  PDE  Comment 
Structure  (g/day) 
Styrene  100-42-5    154  TD50 linear 
extrapolation 
Threshold-based PDE 
Aniline  62-53-3    720  PDE based on 
Aniline HCl  142-04-1  threshold mode of 
action 
(hemosiderosis) 
Endogenous and/or Environmental Exposure 
Acetaldehyde  75-07-0    2,000 (oral)*  Oral PDE is based 
185 (all other  on average food 
routes)  intake; all other 
routes based on 
TD  linear 
50
extrapolation from 
an inhalation study 
Formaldehyde  50-00-0    8,000 or 215  Inhalation route 
ppb, whichever  based on TD50 
is lower  linear extrapolation 
(inhalation)*  or local irritation; 
all other routes 
10,000 (all other 
based on average 
routes) 
food intake 
 
Hydrogen peroxide  7722-84-1      68,000 or 0.5%,  68 mg/day is 1% of 
whichever is  estimated 
lower  endogenous 
production 
Vinyl acetate  108-05-4    2,000 (oral)*  Oral PDE is based 
758 (all other  on average food 
routes)  intake for 
acetaldehyde; all 
other routes based 
on TD  linear 
50
extrapolation from 
an inhalation study 
Other Cases 
p-Chloroaniline  106-47-8    34  AI based on liver 
p-Chloroaniline HCl  20265-96-7  tumors for which 
mutagenic mode of 
action cannot be 
ruled out 
  32  Contains Nonbinding Recommendations 
Compound  CAS#  Chemical  AI  or  PDE  Comment 
Structure  (g/day) 
Dimethyl Sulfate  77-78-1    1.5  Carcinogenicity 
data available, but 
inadequate to 
derive AI. Default 
to TTC 
CAS = Chemical Abstracts Service; AI = acceptable intake; PDE = permissible daily exposure; g = microgram; 
TD  = 50 percent tumor incidence; ppb = parts per billion; mg = milligram; TTC = threshold of toxicological 
50
concern. 
* Route-specific limit. 
 
  33