Generic substitution of antidiabetic drugs in the elderly does not affect adherence

The possibility that variation in packaging and pill appearance may reduce adherence is a reason for concern, especially for chronic diseases. The objectives of the study were to quantify the extent of switches between generic antidiabetics and to verify whether switching between different products of the same substance affects adherence.

All elderly residents of the Umbria Region who received at least 2 prescriptions of antidiabetics in 2010 and 2011 were included in the study. Switching was defined as the dispensing of two different products of the same substance in a series of two prescriptions. Single and multiple switchers were identified according to the number of switches during 2011. Switching relevant to the three off-patent substances with generic use ≥ 5% (metformin, gliclazide and repaglinide) was quantified. The effect of switching on adherence, defined as the proportion of days in 2011 covered by prescriptions (Medication Possession Ratio, MPR), was estimated.

Among the 15 964 patients receiving antidiabetics (14.4% of the elderly population) 9211 were prescribed at least one of the generic substances. Of these patients, 23.3% experienced a single switch and 15.7% were multiple switchers (61.0% never switched). The proportion of multiple switchers increased with the number of prescriptions, reaching 26% among patients with ≥ 11 prescriptions. MPR was 62%, 62% and 72%, respectively among non-switchers, single and multiple switchers.

In elderly patients treated with antidiabetics, the substitution between branded and unbranded products (as well as between generics) of the same substance, did not negatively affect adherence.