Introduction. Medication nonadherence can have a significant
negative impact on treatment effectiveness. Standard intention-to-treat analyses
conducted alongside clinical trials do not make adjustments for nonadherence.
Several methods have been developed that attempt to estimate what treatment
effectiveness would have been in the absence of nonadherence. However, health
technology assessment (HTA) needs to consider effectiveness under real-world
conditions, where nonadherence levels typically differ from those observed in
trials. With this analytical requirement in mind, we conducted a review to
identify methods for adjusting estimates of treatment effectiveness in the
presence of patient nonadherence to assess their suitability for use in HTA.
Methods. A “Comprehensive Pearl Growing” technique, with
citation searching and reference checking, was applied across 7 electronic
databases to identify methodological papers for adjusting time-to-event outcomes
for nonadherence using individual patient data. A narrative synthesis of
identified methods was conducted. Methods were assessed in terms of their
ability to reestimate effectiveness based on alternative, suboptimal adherence
levels. Results. Twenty relevant methodological papers covering 12
methods and 8 extensions to those methods were identified. Methods are broadly
classified into 4 groups: 1) simple methods, 2) principal stratification
methods, 3) generalized methods (g-methods), and 4) pharmacometrics-based
methods using pharmacokinetics and pharmacodynamics (PKPD) analysis. Each method
makes specific assumptions and has associated limitations. Five of the 12
methods are capable of adjusting for real-world nonadherence, with only
g-methods and PKPD considered appropriate for HTA. Conclusion. A
range of statistical methods is available for adjusting estimates of treatment
effectiveness for nonadherence, but most are not suitable for use in HTA.
G-methods and PKPD appear to be more appropriate to estimate effectiveness in
the presence of real-world adherence.