[Are drugs taken as prescribed?]

Abstract

Background: The term "adherence" is used to describe whether drugs are taken as prescribed. This article outlines what is known about adherence for several central drug classes, which factors modify adherence, the consequences of low adherence and how adherence can be improved.

Methods: We reviewed a selection of studies of adherence for the following seven drug classes: antidiabetics, antiepileptics, antihypertensives, statins, psychotropic drugs, antibiotics and analgesics.

Results: For antidiabetics, the proportion of patients with high adherence varied between 31 % and 80 % in the different studies. The corresponding figures for the other drug classes were: antiepileptics, 61-74 %; antihypertensives, 23-73 %; statins, 25-44 %; psychotropic drugs, 21-80 %; antibiotics, 41-70 % and analgesics, 41-53 %. As a general rule, adherence declined with time. For serious diseases, a decline in adherence led to a worsening of symptoms and an increased risk of hospitalisation and death. Dosing once daily proved to result in higher adherence than multiple daily dosing. Complex therapy regimes, depression, impaired cognitive function, side effects and inadequate follow-up reduce adherence.

Interpretation: It is important to achieve high adherence, not least for serious diseases. In order to improve adherence it is necessary to identify patients who have low adherence, understand why the patient does not take the drugs and whether there are any practical problems related to intake. Good communication between patient and doctor is a key factor.