ABSTRACT

This PhD dissertation comprises an overview and three papers for international journals. The work was carried out at the Research Unit of General Practice, University of Southern Denmark, Odense, during 2000-2003.

The consumption of antidepressants has been increasing since the introduction of new generation drugs with milder side-effects in the late 1980s. The use has been criticised by researchers, clinicians and politicians claiming undertreatment, a broadening of the indication area, increasing costs, etc. Knowledge about patients using antidepressants and prescribing patterns among general practitioners is, however, sparse and the purpose of this dissertation was to study the influence of patient and physician characteristics on the use of antidepressants. Special emphasis was on differences in general practitioners' (GPs') prescribing patterns and patients' social background and prior psychiatric history.

Three pharmacoepidemiological studies were carried out using established registers covering the total population in the County of Funen (~470.000 inhabitants/307 general practitioners): the prescription database Odense University Pharmacoepidemiologic Database, the National Health Insurance Register, the Danish Psychiatric Central Register and Statistics Denmark.

During 1998, first time prescription of antidepressants in the population was more frequent among lower socio-economic groups and females, and increasing with age. Early discontinuation, i.e. no purchase of antidepressants six months following first prescription, was observed for every third patient in general practice new to treatment (n=4860, first prescription during January 1998-June 1999). Early discontinuation was more frequent among patients of low socio-economic status and patients prescribed in high-prescribing practices. A substantial variation in GPs' prescribing of antidepressants was observed, but the variation was not larger than for other drug groups. GPs who prescribed antidepressants for a large number of their patients were high prescribers of drugs in general and used more drugs per patient. An association specific to the antidepressants was observed between prescribing rate and GPs' use of psychiatric counselling in the consultation. We did not confirm our hypothesis that selection between new and old generation antidepressants for first-time users is influenced by socio-economic status. Patients with former psychiatric admission were more often prescribed new generation antidepressants, but affective disorders as a specific diagnostic category lowered the preference. It seems reasonable that adherence-promoting strategies pay some attention to high prescribing GPs and patients of low socio-economic status.