Drug-Drug Interaction 
Assessment for 
Therapeutic Proteins 
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) 
 
June 2023 
Clinical Pharmacology 
 
    
Drug-Drug Interaction 
Assessment for 
Therapeutic Proteins 
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) 
 
June 2023 
Clinical Pharmacology 
 
  Contains Nonbinding Recommendations 
 
TABLE OF CONTENTS 
 
 
 
I.  INTRODUCTION............................................................................................................. 1 
II.  CONSIDERATIONS FOR ASSESSING DDIS FOR THERAPEUTIC PROTEINS 2 
III.  TYPES OF DDI ASSESSMENTS AND STUDY DESIGN CONSIDERATIONS ..... 5 
IV.  LABELING RECOMMENDATIONS............................................................................ 7 
V.  APPENDIX. DECISION TREE ...................................................................................... 8 
i  Contains Nonbinding Recommendations 
 
Drug-Drug Interaction Assessment for Therapeutic Proteins 
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  
 
The purpose of this guidance is to help sponsors of investigational new drug (IND) applications 
and applicants of biologic license applications (BLAs) determine the need for drug-drug 
interaction (DDI) studies for a therapeutic protein by providing recommendations for a 
systematic, risk-based approach.2,3 
 
For this guidance, a therapeutic protein refers to a protein that is being developed for licensure, 
or is licensed, as a biological product under section 351 of the Public Health Service Act (42 
U.S.C. 262).4,5 Therapeutic proteins include purified monoclonal antibodies, cytokines, enzymes, 
and other novel proteins for in vivo use. Therapeutic proteins do not include proteins intended to 
act as vaccines or allergenic products, cellular and gene therapy products, and/or human cells, 
tissues, and cellular and tissue-based products.5 Although this guidance applies to therapeutic 
proteins, many of the general principles may be applicable to other biological products, such as 
novel products regulated by CBER (e.g., cellular and gene therapies). Due to the evolving 
knowledge of novel products, sponsors should consult corresponding review divisions for 
detailed information regarding a specific DDI assessment.  
 
1 This guidance has been prepared by the Office of Clinical Pharmacology in the Center for Drug Evaluation and 
Research in collaboration with the Center for Biologics Evaluation and Research at the Food and Drug 
Administration. 
 
2 Schrieber SJ, EP Fletcher, XF Wang, YM Wang, S Sagoo, R Madabushi, SM Huang, and I Zineh, 2019, 
Considerations for Biologic Product DrugDrug Interactions: A Regulatory Perspective, Clin Pharmacol Ther, 
105:1332-1334. 
 
3 Hereafter, the term sponsors will refer to either applicants or sponsors. 
 
4 Section 351 of the Public Health Service Act, 42 U.S.C.  282.   
 
5 More information on therapeutic proteins regulated by CDER and CBER can be found on the FDA web page 
Transfer of Therapeutic Products to the Center for Drug Evaluation and Research available at: 
https://www.fda.gov/combination-products/jurisdictional-information/transfer-therapeutic-biological-products-
center-drug-evaluation-and-research. 
 
  1  Contains Nonbinding Recommendations 
 
 
This guidance supplements the FDA guidances entitled In Vitro Drug Interaction Studies  
Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions and Clinical Drug 
Interaction Studies  Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions 
(January 2020).6,7  
 
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 use of 
the word should in Agency guidance means that something is suggested or recommended, but 
not required. 
 
 
II.  CONSIDERATIONS FOR ASSESSING DDIS FOR THERAPEUTIC PROTEINS 
 
When evaluating the potential for a DDI between a therapeutic protein and small molecules or 
between therapeutic proteins, sponsors should take into account various factors including the 
potential mechanism for the interaction, disease type and severity (if the DDI mechanism is 
related to the disease condition), biological product type, clearance pathways of the therapeutic 
protein, and commonly co-administered drugs in the proposed patient population(s).8,9  
 
Below are examples for which DDI studies of a therapeutic protein could be warranted. This list 
is not all-inclusive, as the development of novel therapeutic proteins will continue to inform the 
DDI risk. Also, refer to the decision tree in the Appendix. 
 
A.  Mechanisms Related to Proinflammatory Cytokines  
 
Therapeutic proteins that are proinflammatory cytokines (e.g., peginterferon) or therapeutic 
proteins that cause increases in proinflammatory cytokine levels (e.g., IL-6) can downregulate 
the expression of cytochrome P450 (CYP) enzymes (e.g., blinatumomab), thereby decreasing the 
 
6 For the most recent version of a guidance, check the FDA guidance web page at 
https://www.fda.gov/RegulatoryInformation/Guidances/default.htm. 
 
7 For recommendations on assessing the DDI potential of antibody-drug conjugates, please refer to the FDA draft 
guidance entitled Clinical Pharmacology Considerations for Antibody-Drug Conjugates (February 2022). When 
final, this guidance will represent the Agencys current thinking on this topic. 
 
8 Kraynov E, SW Martin, S Hurst, OA Fahmi, M Dowty, C Cronenberger, CM Loi, B Kuang, O Fields, S Fountain, 
M Awwad, and D Wang, 2011, How Current Understanding of Clearance Mechanisms and Pharmacodynamics of 
Therapeutic Proteins Can Be Applied for Evaluation of Their Drug-Drug Interaction Potential, Drug Metab and 
Disp, 39:1779-1783. 
 
9 Jing X, P Ji, SJ Schrieber, EP Fletcher, C Sahajwalla, 2020, Update on Therapeutic Protein-Drug Interaction: 
Information in Labeling, Clin Pharmacokinet, 59:25-36. 
 
  2  Contains Nonbinding Recommendations 
 
metabolism of drugs that are CYP substrates and increasing their exposure levels.10 Conversely, 
therapeutic proteins that reduce cytokine levels (e.g., TNF inhibitors) can relieve the CYP 
downregulation from an inflammatory environment (e.g., rheumatoid arthritis), thereby 
increasing CYP expression and activity and reducing exposure of drugs that are CYP substrates.  
 
Although there are data suggesting potential effects of cytokines on transporters based on 
information from in vitro assays or animal models, the translation to clinical significance is 
unknown.11 Investigating the potential for DDIs between cytokines or products that modulate 
cytokines and transporters in clinical studies will help inform risk mitigation strategies. 
 
1.  Therapeutic Protein is a Proinflammatory Cytokine  
 
Sponsors should evaluate the DDI potential for therapeutic proteins that are proinflammatory 
cytokines (see Appendix). 
 
2.  Therapeutic Protein is a Proinflammatory Cytokine Modulator            
 
a.  Therapeutic protein causes an increase in proinflammatory cytokine  
levels   
 
The increase in cytokine levels following administration of a therapeutic protein can be transient 
or persistent. Transient elevation of cytokines might not lead to a clinically relevant interaction. 
Sponsors should determine the time course and extent of any increase in cytokine levels in 
clinical studies to inform whether a DDI study is warranted, the design of a study, and an 
appropriate risk mitigation strategy, if necessary. If the sponsor determines that the DDI potential 
of a therapeutic protein is low, the sponsor should discuss that with the appropriate FDA review 
division and provide a justification for this determination (see Appendix).  
 
b.  Therapeutic protein modulates proinflammatory cytokines in conditions 
associated with elevated cytokine levels   
 
Levels of proinflammatory cytokines differ by disease and severity of disease, leading to 
variability in CYP expression, which makes it challenging to design a DDI study that can be 
extrapolated beyond the study population. Hence, the labeling for such proinflammatory 
cytokine modulators should include language indicating the potential for a DDI in conditions 
associated with elevated cytokine levels. 
 
 
10 Lee J, L Zhang, AY Men, LA Kenna, and SM Huang, 2010, CYP-Mediated Drug-Therapeutic Protein 
Interactions: Clinical Findings, Proposed Mechanisms and Regulatory Implications, Clin Pharmacokinet, 49:295-
310. 
 
11 Cressman AM, V Petrovic, and M Piquette-Miller, 2012, Inflammation-mediated Changes in Drug Transporter  
Expression/activity: Implications for Therapeutic Drug Response, Expert Rev Clin Pharmacol, 5:69-89. 
 
  3  Contains Nonbinding Recommendations 
 
Sponsors should provide justification for the exclusion of labeling language indicating the 
potential for a DDI if the data support that the potential for clinically significant DDI is low.12,13 
Examples for justifications could include a discussion of: 
 
  DDI effects observed with other agents or the same agent in other disease states with 
similar or more inflammatory burden 
 
  Differences in exposure levels of sensitive CYP substrates in healthy subjects versus the 
indicated population considering other covariates  
 
  Magnitude of cytokine modulation by the therapeutic protein 
 
Alternatively, sponsors can assess the DDI potential in a clinical study to further inform labeling. 
The clinical study can be a stand-alone DDI study or a nested DDI study as part of a larger 
clinical study in which the primary objective is not to evaluate DDIs (see section III.C). The 
disease type and severity and dosage(s) are important considerations. If a therapeutic protein is 
being developed for multiple indications, the potential for DDIs should be evaluated in patients 
with the indication manifesting the most severe inflammatory burden.12  
 
B.  Mechanisms Unrelated to Proinflammatory Cytokines   
 
There are observed or postulated DDIs with therapeutic proteins that are not caused by 
proinflammatory cytokines. Depending on the expected mechanism of the DDI, sponsors should 
evaluate the effect of a therapeutic protein on other drugs or the effect of other drugs on the 
therapeutic protein. Scenarios in which DDI evaluation should be considered include:  
 
  A therapeutic protein that affects human physiological processes (e.g., GLP-1 receptor 
agonists such as dulaglutide and albiglutide result in delayed gastric emptying) and 
thereby alters the pharmacokinetic profiles of co-administered drugs. In such cases, 
sponsors should evaluate the potential for a therapeutic protein to affect the other drug(s).   
 
  A concomitantly administered medication that impacts the distribution of the therapeutic 
protein to the site of target14,15 or the target-mediated disposition of the therapeutic 
 
12 Coutant DE and SD Hall, 2018, Disease-Drug Interactions in Inflammatory States Via Effects on CYP-Mediated 
Drug Clearance, J Clin Pharmacol, 58:849-863. 
 
13 Sathe AG, AA Othman, MF Mohamed, 2021, Therapeutic Protein Drug Interaction Potential in Subjects With 
Psoriasis: An Assessment Based on Population Pharmacokinetic Analyses of Sensitive Cytochrome P450 Probe 
Substrates, J Clin Pharmacol, 61:307-318.  
 
14 Abuqayyas L and JP Balthasar, 2012, Pharmacokinetic mAb-mAb Interaction: Anti-VEGF mAb Decreases the 
Distribution of Anti-CEA mAb into Colorectal Tumor Xenografts, AAPS J, 14:445455. 
 
15 Pastuskovas CV, EE Mundo, SP Williams et al, 2012, Effects of Anti-VEGF on Pharmacokinetics, 
Biodistribution, and Tumor Penetration of Trastuzumab in a Preclinical Breast Cancer Model, Mol Cancer Ther, 
11:752-762. 
 
  4  Contains Nonbinding Recommendations 
 
protein.16 In such cases, depending on the role of the therapeutic protein in the DDI, 
sponsors should evaluate the DDI potential of the therapeutic protein to affect the other 
drug(s) or be affected by the other drug(s). 
 
  A concomitantly administered therapeutic protein that affects another therapeutic 
proteins interaction with the FcRn (e.g., saturating, blocking, or interfering with the 
interaction between therapeutic proteins containing an Fc region of human IgG and 
FcRn) and decreases the exposure of the therapeutic protein.17,18 In such cases, depending 
on the role of the investigational therapeutic protein in the DDI, sponsors should evaluate 
the DDI potential of the therapeutic protein to affect the other drug(s) or be affected by 
the other drug(s). 
 
  A concomitantly administered immunosuppressor with a therapeutic protein whose 
pharmacokinetics are affected by immunogenicity (e.g., methotrexate on the clearance of 
adalimumab).19,20  In such cases, the potential of the other drug to affect the therapeutic 
protein should be evaluated. This type of DDI evaluation can be difficult to prospectively 
design, and as such, a descriptive analysis can often be considered adequate.  
 
 
III.  TYPES OF DDI ASSESSMENTS AND STUDY DESIGN CONSIDERATIONS   
  
Using a systematic, science-driven approach to evaluate the DDI potential of therapeutic proteins 
is highly recommended and can involve a combination of the assessment types listed below. 
Sponsors should consider the DDI risk of their therapeutic protein early in development and 
summarize their DDI evaluation program at milestone meetings with the FDA. Potential 
discussion topics at these meetings include the need for and planning, timing, and study design 
of DDI evaluations for the investigational therapeutic protein. 
 
A.  In Vitro and Animal Studies   
 
In vitro or animal data have not been predictive of the potential for clinical DDIs with 
therapeutic proteins. However, such data could provide a mechanistic understanding of the DDI 
potential of a therapeutic protein. Sponsors are encouraged to discuss their specific DDI study 
plans with the FDA. 
 
16 Lavezzi SM, JD Jong, M Neyens et al, 2019, Systemic Exposure of Rituximab Increased by Ibrutinib: 
Pharmacokinetic Results and Modeling Based on the HELIOS Trial, Pharm Res, 36:93. 
 
17 Hansen RJ and JP Balthasar, 2002, Intravenous Immunoglobulin Mediates an Increase in Anti-Platelet Antibody 
Clearance via the FcRn Receptor, Thromb Haemost, 88:898899. 
 
18 USPI of VYVGART, Sections 7.1 and 12.3. 
 
19 Pouw MF, CL Krieckaet, MT Nurmohamed, DV Kleij, L Aarden, T Rispens, and G Wolbink, 2015, Key Findings 
towards Optimising Adalimumab Treatment: the Concentration-effect Curve, Ann Rheum Dis, 74:513518. 
 
20 USPI of Humira, Section 12.3.   
 
  5  Contains Nonbinding Recommendations 
 
 
B.  Dedicated Clinical Studies 
 
Clinical studies designed to evaluate the potential for DDIs with a therapeutic protein should 
consider the mechanism for the DDI and safety when selecting the relevant study population and 
the interacting drugs.  
 
The study design (parallel or crossover) should be informed by the mechanism for the DDI, the 
pharmacokinetic (PK) characteristics of the drugs (e.g., the drugs half-life), and the 
immunogenicity risk of the therapeutic protein, for example: 
 
  When the effect of other drug(s) on  the therapeutic protein is evaluated, a parallel design 
might be appropriate when the therapeutic protein has a long half-life.  
 
  When evaluating the effect of the therapeutic protein on the other drug(s) (e.g., the effect 
of proinflammatory cytokines or proinflammatory cytokine modulators on CYP 
substrates), a single-sequence, crossover design can be used (i.e., substrate alone 
followed by the substrate plus the therapeutic protein). 
  
-  The sponsor should determine the time course for cytokine modulation by the 
therapeutic protein in the specific disease state to guide the timing and duration of 
administration of the substrate and therapeutic protein in the study.  
 
-  A cocktail approach (i.e., simultaneous administration of substrates of multiple CYP 
enzymes) is an efficient means of evaluating the DDI potential for therapeutic 
proteins where multiple CYPs could be impacted (e.g., proinflammatory cytokines 
and proinflammatory cytokine modulators).21  
 
C.  Population PK Modeling (Nested DDI Studies)   
 
Population PK analyses can be informative in evaluating the DDI potential of therapeutic 
proteins.22,23 A population PK analysis for prospective DDI evaluation should have carefully 
designed study procedures and protocols for the collection of PK samples, as well as clear 
documentation of the timing of administrations and the types of concomitant medications for 
which DDI is being assessed. In general, this approach is used to evaluate the effect of other 
agents on the investigational therapeutic protein, as PK data are usually collected for the 
 
21 Jing X, P Ji, SJ Schrieber, EP Fletcher, C Sahajwalla, 2020, Update on Therapeutic Protein-Drug Interaction: 
Information in Labeling, Clin Pharmacokinet, 59:25-36. 
 
22 Chow AT, JC Earp, M Gupta, W Hanley, C Hu, DD Wang, S Zajic, and M Zhu, 2014, Population PK TPDI 
Working Group: Utility of Population Pharmacokinetic Modeling in the Assessment of Therapeutic Protein-Drug 
Interactions, J Clin Pharmacol, 54:593-601. 
 
23 Kenny JR, MM Liu, AT Chow, JC Earp, R Evers, JG Slatter, DD Wang, L Zhang, and HH Zhou, 2013, 
Therapeutic Protein DrugDrug Interactions: Navigating the Knowledge Gaps - Highlights from the 2012 AAPS 
NBC Roundtable and IQ Consortium/FDA Workshop, AAPS J, 15:933-940. 
 
  6  Contains Nonbinding Recommendations 
 
investigational agent only. However, a sponsor can prospectively plan and collect the necessary 
data for a substrate of interest to support the evaluation of the effect of the investigational 
therapeutic protein on the substrate of interest. For a discussion on nested DDI studies, refer to 
the FDA guidances entitled Clinical Drug Interaction Studies  Cytochrome P450 Enzyme- and 
Transporter-Mediated Drug Interactions (January 2020) and Population Pharmacokinetics 
(February 2022). 
 
D.  Other Modeling Approaches 
 
The application of physiologically based PK (PBPK) modeling in the evaluation of the DDI 
potential of a therapeutic protein is an emerging area. PBPK modeling has a potential role in 
understanding the underlying mechanism of a DDI. For more information, see the FDA guidance 
entitled Physiologically Based Pharmacokinetic Analyses  Format and Content (September 
2018). 
 
Other modeling approaches could be considered, and sponsors are encouraged to discuss the 
proposed approach with the FDA.  
 
 
IV.  LABELING RECOMMENDATIONS 
 
Prescribing Information must include a summary of essential DDI information needed for the 
safe and effective use of the drug by the healthcare provider.24 For specific requirements and 
recommendations regarding how to incorporate DDI information in labeling, refer to 21 CFR 
201.57 and the following FDA guidances:25 
 
  Labeling for Human Prescription Drug and Biological Products  Implementing the 
PLR Content and Format Requirements (February 2013) 
 
  Warnings and Precautions, Contraindications, and Boxed Warning Sections of Labeling 
for Human Prescription Drug and Biological Products  Content and Format (October 
2011) 
 
  Clinical Pharmacology Section of Labeling for Human Prescription Drug and 
Biological Products  Content and Format (December 2016)  
 
  Patient Counseling Information Section of Labeling for Human Prescription Drug and 
Biological Products Content and Format (December 2014) 
 
 
 
 
24 21 CFR 201.56(a)(1). 
 
25 See also the FDA draft guidance entitled Dosage and Administration Section of Labeling for Human Prescription 
Drug and Biological Products  Content and Format (January 2023). When final, this guidance will represent the 
Agencys current thinking on this topic. 
  7  Contains Nonbinding Recommendations 
 
 
V.  APPENDIX. DECISION TREE 
 
No 
further
action
Yes Yes
Provide scientific 
justification for no  Adequate 
Include  interaction potential  justification
labeling  (see Section IIA) 
Pro-inflammatory 
language indicating 
cytokine  No
potential for CYP-
modulator TPs No
mediated drug  Conduct DDI 
Interaction# evaluation*                      
(see Section III) 
Pro-inflammatory 
cytokine TPs
Yes
Label 
Known 
appropriately# 
TPs not included  or suspected  No 
in the above  mechanisms  No further 
categories  for DDI (see action
Section IIB)
 
CYP, cytochrome P450; DDI, drug-drug interaction; TP, therapeutic protein. 
*The Agency recommends that DDI evaluation proposals be discussed with the appropriate review division before 
initiating a study. 
#Refer to Section IV. 
 
 
 
  8