A real world comparison of methods for assessing dosing patterns of biologic therapies for psoriasis

Background: Biologic therapies for psoriasis may require changes in dosage regimen which may affect clinical & cost effectiveness, & likelihood of adverse events. There is lack of consensus on the optimal method to evaluate dosing patterns. Objectives: To compare different analytic methods to evaluate dosing patterns for adalimumab (ADA), etanercept (ETN) & ustekinumab (UST) using the British Association of Dermatologists Biologic Interventions Register. Methods: Patients were included if they were followed-up for ≥12-months & had complete records of dosing information. Five methods for assessing dosing patterns were compared descriptively: last vs. index dose (ID; dose of biologic therapy at enrolment); average vs. recommended dose; multiple instances of subsequent doses different from the ID; subsequent doses different from ±30% of the ID; & time-trend method comparing the annual cumulative dose (CD) received to the recommended CD. Results: Overall 2980 patients (ADA:1675; ETN:996; UST:309) were included. Estimates of dose escalation (DE) were lowest for all drugs using the last vs. ID method (ADA,1%; ETN,4%; UST,15%) while the average dose method gave the highest estimates (ADA,5%; ETN,12%; UST,26%). In contrast, the average dose method gave the smallest estimates of dose reduction (DR) for all drugs (ADA,1%; ETN,1%; UST,25%) while the time-trend method gave the highest rates (ADA,3%; ETN,5%; UST,30%).The multiple incidences & the threshold approaches yielded similar findings for both DE & DR for all drugs. These rates were also similar to those determined using the last vs. ID method for ADA & ETN, but differed for UST. In all but one case, higher rates for changes in utilisation of UST were due to differences with administration intervals rather than prescribed dose. Conclusions: Different methods yielded diverse estimates using the same data, but consistently gave the same overall finding that UST patients had higher rates of change in dosage patterns, regardless of the method. The time-trend method provided the most comprehensive measure on usage patterns taking account of both frequency & timing of changes in regimen, which differed from the other approaches.