The effect of generic switching on concerns about medicine and non-persistence among Danish adults in a general...

Generic substitution means that one medicinal product is replaced by another product containing the same active substance. Generic substitution has existed in Denmark since 1991, and pharmacies are obliged to substitute a generic version of a medication, unless the general practitioner (GP) has explicitly stated that it should not be done, or the patient insists on having the more expensive drug.  Generic prescribing, that is prescribing the substance name, is not allowed in Denmark. Some specialists and patients cast doubt on the real interchange-ability of generics, although international studies have shown that most patients have positive attitudes towards generic substitution. The severity of disease is known to be associated with patients being more concerned about generic substitution. The generic substitution scheme implies changing from one drug to another that may vary in brand-name, form, size, colour and taste. Speculations have been raised as to whether these medication changes between generic brands or from brand-name drugs to generics or vice versa may cause patient concerns. Qualitative studies have shown problems in recognising the substituted medicine and lack of confidence in the identical effect of the substitutable medicines. Several studies have focused on one specific drug group such as antihypertensive drugs. However, the influence of generic switching may affect concerns about medicine differently, depending on drug categories. Research on generic substitution often focuses on incident drug users, whose prescription is substituted at their first redemption. Most of these studies did not identify significant associations between generic substitution and non-adherence, but one study assessing the association between generic substitution and persistence showed reduced persistence. So far, studies of the effect of generic drug substitution on drug continuation have not focused on patients' overall experience of generic switches within one specific drug.

To analyse associations between generic substitution and patient characteristics as well as patients' views on generic medicines, confidence in the healthcare system, beliefs about medicine, and experience with earlier generic substitution. To investigate the possible association between a specific generic switch and patients' concerns about their medicine. To examine how generic switch influences persistence with long-term treatment with special focus on importance of patients' concerns and views on generic medicine.

The design was a combined cross-sectional questionnaire and register study and additionally a cohort study. The study was conducted among 6,000 medicine users, who had redeemed generically substitutable drugs with general reimbursement in September 2008 (2,000 users of antidepressants, 2,000 users of antiepileptics and 2,000 users of other substitutable drugs), who were aged 20 years or older and living in the Region of Southern Denmark. The medicine users were identified through Odense PharmacoEpidemiologic Database (OPED). The purpose of the questionnaire survey was to elucidate patients' experience with medicine, combined with information from OPED on a single well-defined generic switch of the index drug. The questionnaire was adapted to the individual subject with reference to their specific drug (index drug) in every question and index date printed on the questionnaire. The questionnaire comprises scales from the validated Beliefs about Medicine Questionnaire (BMQ) and ad hoc constructed scales. By means of OPED data it was possible to conduct a cohort study comprising information on all purchased medicine during the 12 months following the index date. The cohort comprised users of antidepressants and users of antiepileptics.

A total of 2,476 patients (44.1%) were included in the analyses. Experience with earlier generic switches within the index ATC code was associated with experience of a generic switch on the index day (OR 5.93; 95% CI 4.70-7.49). However, experience with earlier generic switches was drug-specific, e.g. having had more than five earlier switches within other ATC codes reduced the odds of experiencing a generic switch on the index day. Having negative views on generic medicines also reduced the odds of experiencing a generic switch on the index day. The second study showed no statistically significant associations between experiencing a generic switch on the index day and having more or less concerns about the index medicine (-0.02 95% CI: -0.10-0.05). Patients experiencing their first-time switch of a specific drug were at higher risk of non-persistence, hazard ratio 2.98, 95% CI 1.81-4.89, versus those who have never switched, and 35.7% became non-persistent during the first year of follow-up. Generic switching did not influence persistence considerably in those having previous experience with generic switching of the specific drug.

The overall results from the thesis showed that experience with earlier generic switches of a specific drug was associated with making a future generic switch and did not cause additional concerns about the index medicine. The effect of previous experience with generic substitution has been shown to be drug-specific. The third study showed that patients, who are first-time switchers of a specific drug, were at higher risk of becoming non-persistent compared to never switchers and those having experienced previous generic switching.