Guidance for Industry 

Integration of Dose-Counting
 
Mechanisms into MDI Drug
 
Products
 
U.S. Department of Health and Human Services
 
Food and Drug Administration
 
Center for Drug Evaluation and Research (CDER)
 
Clinical Medical
 
March 2003
  Guidance for Industry 

Integration of Dose-Counting
 
Mechanisms into MDI Drug
 
Products
 
Additional copies are available from: 
Office of Training and Communications 
Division of Communication Management 
Drug Information Branch, HFD-210 
5600 Fishers Lane 
Rockville MD 20857 
(Tel): 301-827-4573 
(Internet)  http://www.fda.gov/cder/guidance/index.htm 
U.S. Department of Health and Human Services
 
Food and Drug Administration
 
Center for Drug Evaluation and Research (CDER)
 
Clinical Medical
 
March 2003  Table of Contents 
I.  INTRODUCTION................................................................................................................. 1
 
II.  BACKGROUND ...................................................................................................................2
 
III.  INTEGRATION OF DOSE-COUNTING MECHANISMS INTO MDI PRODUCTS 

UNDER DEVELOPMENT.......................................................................................................... 3
 
A.  General Recommendations...........................................................................................................3
 
B.  Reliability Issues............................................................................................................................. 3
 
C.  Other Considerations.....................................................................................................................4
  Contains Nonbinding Recommendations 
Guidance for Industry 1
 
Integration of Dose-Counting Mechanisms into 

MDI Drug Products 

This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It 
does not create or confer any rights for or on any  person and does not operate to bind FDA or the public. 
An alternative approach may be used if such approach satisfies the requirements of the applicable statutes 
and regulations. If you want to discuss an alternative approach, contact the FDA staff responsible for 
implementing this guidance.  If you cannot identify the appropriate FDA staff, call the appropriate 
number listed on the title page of this guidance. 
I.  INTRODUCTION 
This guidance is intended to assist manufacturers who are developing or plan to develop drug 
products for oral inhalation using metered-dose inhalers (MDIs).  The guidance reflects the 
Agency's current recommendations regarding the integration of dose-counting mechanisms into 
MDI drug products for oral inhalation. Although the contents of the guidance should be 
considered by any manufacturer of any MDI drug product (including nasal MDI products), this 
guidance is not specifically intended for manufacturers of already marketed MDI drug products 
for oral inhalation nor for manufacturers developing MDIs for other routes of administration 
(e.g., nasal MDIs). It is also not intended for manufacturers developing multidose dry powder 
inhalers (MDPIs), which already incorporate dose counters as an integral part of the delivery 
system.  Manufacturers developing new MDPIs are encouraged to continue including dose 
counters in their products and may find the contents of this guidance useful in their planning. 
For the purposes of this guidance, the term  dose counter includes both mechanisms that use a 
numeric count to indicated doses remaining, as well as dose-indicating mechanisms that do not 
enumerate the number of actuations, but rather indicate via color coding or other means when a 
device is nearing the end of its useful life.  Also, the use of the term  integrated in this document 
is intended to define dose counters that are an integral part of the MDI canister and/or actuator, 
and not simply an add-on that can be removed and used multiple times with various products. 
FDA's guidance documents, including this guidance, do not establish legally enforceable 
responsibilities. Instead, guidances describe the Agency's  current thinking on a topic and should 
be viewed only as recommendations, unless specific regulatory or statutory requirements are 
                                                
1  This  guidance has been  prepared by the Division  of Pulmonary and Allergy  Drug  Products in the Center for  Drug 
Evaluation and Research (CDER) at the Food and Drug  Administration (FDA). 
1
  Contains Nonbinding Recommendations 
cited. The use of the word should in Agency guidances means that something is suggested or 
recommended, but not required. 
II.  BACKGROUND 
Metered-dose inhalers have been available for nearly 50 years and have come to be regarded as 
the preferred method of delivery for many important drugs intended to treat obstructive airway 
diseases, such as asthma, emphysema, and chronic bronchitis.2  MDIs represent a reliable, 
   
convenient dosing device for delivery of medications to the lungs.  However, they have one 
major disadvantage over other dosage forms.  Currently available MDIs offer no practical way 
for patients to track the remaining numbers of doses or amount of medication.  A complicating, 
but necessary design feature of MDIs is that they contain more formulation than strictly required 
to expel the labeled number of actuations.  This additional amount of formulation (propellant, 
drug substance, and any excipients) is necessary to ensure the dosing consistency of each spray 
through the labeled number.  For instance, an MDI labeled to deliver 120 metered-actuations 
may expel 20 to 30 additional actuations (depending on the specific fill target for that product). 
However, the amount of drug per spray in those additional 20 to 30 actuations may in many 
cases be inconsistent and with continued use beyond the label claim will become negligible. 
Since the inactive components in the drug formulation may exceed 95 to 99 percent, an MDI 
used beyond the recommended dose may appear to be delivering a therapeutic spray when it 
isn't.  Other than carefully and consistently tracking each actuation in writing and subtracting this 
total from the labeled number of actuations, there is no method by which a patient can determine 
how many effective doses are left in an MDI.  Various means of testing the inhalers (e.g., 
shaking the canister) are unreliable and some in addition may damage the MDI (e.g., the float-
test, placing the canister in water). 
Currently, patients must guess how many doses are left in their MDIs and have two practical 
options: (1) throw away an MDI that may still contain acceptable metered-doses or (2) use a 
product when it may be beyond the recommended number of doses and risk not receiving the 
correct drug dose. The former is wasteful, and the latter is potentially dangerous.  The addition 
of an accurate dose counter to an individual MDI unit would allow the patient to reliably track 
the numbers of actuations used from that individual inhaler (i.e., to identify when the label claim 
number of actuations has been reached).  This would prevent the patient from discarding an 
inhaler unnecessarily or using the product beyond the recommendations provided in the labeling 
for that product. 
The recommendations in this guidance address primarily MDI products designed to deliver drugs 
to the lungs for any indication.  This is because the consequences of not receiving an acceptable 
metered dose are more clinically important for oral inhalation drug products than for the current 
medications available in nasal MDIs.  Medications delivered to the lungs often play a vital role 
in the treatment of airway diseases and are potentially life-saving.  Nasally delivered drugs are 
more typically intended to treat bothersome, but non-life-threatening, conditions.  However, if a 
                                                
2  Guidelines for the Diagnosis and Management of Asthma: Expert Panel Report 2,  National Asthma Education and 
Prevention Program  of the National Institutes of Health, NIH publication #97-4051,  April 1997. 
2
  Contains Nonbinding Recommendations 
nasal MDI were developed where the issue of dosing beyond the recommended label claimed 
number of doses were associated with a more serious consequence, this guidance would be 
applicable. 
Finally, this guidance is not intended to preclude other accurate means of informing patients as to 
the remaining number of metered-doses left in an MDI.  If manufacturers develop other ways 
apart from the use of a dose counter, the FDA is willing to consider those innovations and, if 
satisfactory, to deem them reasonable alternatives. 
III.	  INTEGRATION OF DOSE-COUNTING MECHANISMS INTO MDI PRODUCTS 
UNDER DEVELOPMENT 
A.	  General Recommendations 
The Agency recommends that manufacturers with metered-dose inhalers under development for 
oral inhalation integrate a dose-counting device into the development of their MDI drug product. 
Dose counters should provide, either through a direct numeric count or color coding, a clear 
indication of when an MDI is approaching the end of its recommended number of actuations as 
well as when it has reached or exceeded that number.  An indication that an MDI is approaching 
the end of its recommended number of actuations should occur when a sufficient number of 
actuations are left to give patients enough time to obtain a new MDI.  If a numeric count is 
chosen, we recommend that the counter be designed so that it counts downward from the 
recommended number of actuations to zero, rather than counting upwards, enabling patients to 
know when a device is approaching the end of its life (i.e., the number of actuations is 
approaching zero). 
As previously mentioned, this guidance specifically refers to orally inhaled MDI drug products 
currently under development or which are being planned for development.  Although the 
integration of dose counters into currently approved MDIs is also encouraged, it is recognized 
that the economics of doing so may be burdensome, particularly for MDIs using 
chlorofluorocarbons as propellants (since these products will eventually be universally phased-
out under the provisions of the Montreal Protocol on Protection of the Ozone Layer). 
Manufacturers with MDI drug products in the latter stages of development are encouraged to 
integrate a dose counter into their product as soon as feasible, although the integration may not 
be possible prior to submission of a new drug application.  In such cases, manufacturers are 
encouraged to commit to developing an integrated dose counter in the postmarketing period. 
B.	  Reliability Issues 
Dose counters should be engineered to reliably track actuations and should be designed to be as 
close to 100 percent reliable as possible.  However, if some low frequency of error is 
unavoidable, the device should be designed to specifically avoid undercounting (i.e., the MDI 
sprays, but the counter does not advance).  Undercounting could result in patients assuming they 
have medication left in their MDI when they do not, a circumstance that is potentially dangerous. 
The reliability of dose counters should be established during development under in-vitro testing 
3
  Contains Nonbinding Recommendations 
(simulating use and potential abuse), as well as in clinical use.  The documentation of dose 
counter functionality, reliability, and accuracy would ideally be derived from assessments in 
clinical trials including, where possible, phase-3 trials.  However, for dose counters added either 
late in a development program or postapproval, in-use studies should be designed and conducted 
to obtain this information.  Note that in either case, these studies do not need to establish the 
clinical benefit of incorporating a dose counter, rather, they should address issues related to 
ergonomics, ruggedness, and accuracy of the counters in clinical settings.  The range of patients 
in whom this information is developed should include reasonable representation of special 
populations likely to use the drug (e.g., pediatrics, geriatrics).  Finally, if the same dose counter 
design and mechanism is incorporated into multiple different MDIs, it would not ordinarily be 
necessary to repeat the in-use studies for each additional MDI product in which a counter of the 
same design is used, once the in-use data have been satisfactorily developed with the device. 
However, since dosing characteristics vary between MDIs, in-vitro testing would ordinarily be 
expected in all such cases. 
C.  Other Considerations 
A lock-out mechanism to prevent doses beyond the labeled number of actuations would be an 
optional feature of dose counters. However, a lock-out feature would not be recommended for 
bronchodilator medications used to treat acute bronchospasm.  For these rescue bronchodilators, 
the ability of the MDI to actuate beyond the labeled number of actuations and to provide even a 
partially therapeutic dose of drug could be life saving. 
4