Pharmacoeconomic consequences of variable patient compliance with prescribed drug regimens.

Variable compliance with prescribed drug regimens is a leading source of variability in drug response. Specifics differ by drug and disease. The role of variable compliance was clearly defined in 2 trials of lipid-lowering agents, cholestyramine and gemfibrozil, in which exceptionally careful measurements of compliance were made, which has not been done in later trials. Economic consequences of variable compliance are estimated by converting dose-dependent changes in absolute risk of incident coronary disease into the unicohort format, which designates how many patients must be treated to prevent, in a given time, a defined 'coronary event'. Two strong influences on the costs of treatment are: (i) the shape of the relation between drug intake and risk reduction; and (ii) the strength of the linkage between intake and prescription refills. The intake-effect relation for cholestyramine is linear, making compliance-neutral the cost to prevent 1 coronary event, provided that refills match intake. If refills exceed intake, treatment costs rise. The intake-effect relation for gemfibrozil is more typically nonlinear, so poorer compliers purchase and take the drug in amounts that have little benefit, increasing the cost to prevent 1 coronary event. If refills run at a higher rate than intake, costs increase still further. A key question for future study is: do policies that encourage timely refills increase compliance enough to offset their potential to waste money in the purchasing of an untaken drug?