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Relationship Between Adherence Rate Threshold and Drug ‘Forgiveness’

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Abstract

The medication adherence rate (A) is the proportion of prescribed drug doses consumed within a given time period. It is often assumed that there is an adherence rate threshold (A th) at or above which the therapeutic effect of the medication is maintained. Drug forgiveness (F) is the number of consecutive doses that can be missed while still maintaining a therapeutic effect. At a given value for A, the therapeutic effect of the drug will be continuously maintained if there is no possibility of >F missed doses. Hence, for a once-daily drug prescribed for N days, A th and F are related by the formula, A th = (N − F)/N. At adherence rates below A th the probability of maintaining the therapeutic effect is equal to the probability of there being no instances of >F consecutive missed doses. Since F is a function of the duration of the drug effect (D) and D varies depending on the specific drug’s pharmacokinetic/pharmacodynamic properties, there is no universal A th applicable to all drugs.

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Acknowledgements

The authors thank Bob Greenwald for creating the Perl script described in ESM Sect. 3.

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  1. ScribCo, PO Box 580, Effort, PA, 18330, USA

    Alan Morrison, Melissa E. Stauffer & Anna S. Kaufman

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  1. Alan Morrison
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  2. Melissa E. Stauffer
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  3. Anna S. Kaufman
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Correspondence to Alan Morrison.

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No external funding was used in the preparation of this manuscript.

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Alan Morrison, Melissa E. Stauffer, and Anna S. Kaufman declare that they have no conflicts of interest that might be relevant to the contents of this manuscript.

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Morrison, A., Stauffer, M.E. & Kaufman, A.S. Relationship Between Adherence Rate Threshold and Drug ‘Forgiveness’. Clin Pharmacokinet 56, 1435–1440 (2017). https://doi.org/10.1007/s40262-017-0552-2

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