Overview of antidepressant usage among adults - January 2011 (only available in French)

Background

A number of studies report problems with antidepressant usage. Among these concerns, several researchers report that individuals following antidepressant therapy have difficulty adhering to their medication. With limited recent Canadian and Québec findings available, a study of antidepressant use in Québec was necessary.

Objective

The general objective of the study was to provide an overview of antidepressant usage among adults aged 18 and over who were covered by the Public Prescription Drug Insurance Plan over the course of five years, between January 1, 2005 and December, 31 2009. 

Methods

Using administrative databases from the Régie de l’assurance maladie du Québec (RAMQ), a descriptive study was conducted with a retrospective cohort of adults aged 18 and over who were insured by the Public Prescription Drug Insurance Plan. Antidepressant users were identified and, from them, new users were distinguished based on an absence of active antidepressant prescriptions during the 365 days preceding the date their first prescription was filled (the index date). Insurance coverage information and socio-demographic characteristics were obtained from eligibility files for those insured by the Plan. The study relied on medical services to identify medical history, diagnoses and medical interventions, while pharmaceutical services were consulted to characterize the use of various drugs, including antidepressants, between 2005 and 2009.

The annual prevalence of antidepressant use was calculated for the general population based on age, sex, coverage category, and health region. New users and their respective courses of treatment were also described. Trends observed using the Kaplan-Meier method enabled researchers to evaluate adherence to treatment, in other words the period of time during which the individual continued to receive antidepressant therapy following their initial treatment. For new antidepressant users who received a diagnosis of major depression in the three months preceding the beginning of treatment, the quality of antidepressant use was evaluated using four criteria established in line with the 2009 Canadian guidelines for the treatment of major depression. These criteria relate to the selection of first-line antidepressants, prescribed daily dosages, total duration of treatment and frequency of medical follow-up visits.

Results

From 2005 to 2009, the prevalence of antidepressant use among adults aged 18 and over who were covered by the Public Prescription Drug Insurance Plan increased by 8.3%, from 13.3% to 14.4%. Between 2005 and 2009, 345,558 new antidepressant users were reported. Overall, 50.1% of new users were aged 60 and over, and women represented approximately two-thirds of new users. For 63.3% of new users, no mental illness diagnosis frequently treated with antidepressants was found in the database at the index date or in the three months preceding it. The most frequent diagnoses during the same period were major depression (14.7%) and anxiety disorders (14.1%). Between 2005 and 2009, 338,322 of the 345,558 new antidepressant users, in other words almost all of them (97.9%), received only one drug product at the beginning of therapy. In monotherapy, initial treatments most frequently included citalopram (24.3%), tricyclic antidepressants and derivatives (23.4%), venlafaxine (17.5%) and trazodone (12.6%).

New users’ overall adherence to antidepressant therapy at 15 days, 30 days, 2 months, 3 months, 4 months, 6 months, 1 year and 2 years was 93.8%, 63.3%, 56.7%, 49.4%, 44.8%, 38.5%, 28.4% and 20.4% respectively. New users diagnosed with major depression showed stricter adherence than those with anxiety disorders or adjustment disorders across all time periods measured.

Among new antidepressant users who received a diagnosis of major depression in the three months preceding the beginning of treatment, 87.7% of those aged 18 to 64 and 91.3% of those aged 65 and over began their treatment with a first-line agent, whereas 84.9% of those aged 18 to 64 and 72.3% of those aged 65 and over received a dose compliant with recommended dosage frequencies three months into their treatment. Only 31.9% of new users aged 18 to 64 and 44.9% of new users aged 65 and over received antidepressant therapy for a total of eight months or more. Lastly, 15.5% of new users aged 18 to 64 and 25.5% of those aged 65 and over attended eight or more medical visits in the twelve months following the date their therapy began.

Conclusion

In recent years, the prevalence of antidepressant use among adults in Québec covered by the Public Prescription Drug Insurance Plan increased consistently, from 13.3% in 2005 to 14.4% in 2009. Antidepressant adherence, however, was problematic, as only 38.5% of all new antidepressant users (irrespective of diagnosis) and 46.3% of those who received a diagnosis of major depression continued to follow therapy after six months. As for the quality of antidepressant use among new users diagnosed with major depression, the criteria for choosing the initial agent and prescribed daily dosages were generally respected. The total duration of therapy, however, was less than eight months in the majority of cases, and few medical follow-up visits were attended in the year following the beginning of therapy. Further studies are suggested in order to determine the factors hindering antidepressant adherence among the general population in Québec and to implement solutions targeting the identified factors. Moreover, for the benefit of those individuals diagnosed with major depression, better follow-up has to be made on therapy for depressive episodes. In this way, the overall management of the individual and their treatment by a team of health professionals (doctors, pharmacists, nurses and other stakeholders) can become an attractive solution. A joint follow-up could also eventually promote stricter adherence to antidepressant therapy.