Prescription of antidepressants to patients on opioid maintenance therapy – a pharmacoepidemiological study

Background and aims: Depression and anxiety are commonly reported among patients in opioid maintenance treatment (OMT). The aim of the present study was to describe aspects of prescription of antidepresant drug therapy among patients on OMT. Our research questions were: 1) What is the prevalence of antidepressant use according to age and gender? 2) Which antidepressants are used? 3) How are antidepressants used in terms of reimbursement codes, dispensed dose and duration of therapy? Methods: Pharmacoepidemiological data were retrieved from the complete national Norwegian Prescription Database which contains information on all prescription drugs (such as Anatomical Theraputical Chemical (ATC)-code, Defined Daily Dose (DDDs)), dispensed at pharmacies to individual patients. Norwegian OMT-patients (N=4374, 3035 men and 1339 women) who received methadone mixture, buprenorphine capsules or combined buprenorphine-naloxone capsules for at least 6 months in 2009 were included. Prevalence of antidepressant use in the studied patients was measured in terms of retrieval of prescriptions. Results: During 2009 21.7% of the studied patients filled at least one prescription for an antidepressant drugs (men: 21.2%; women: 22.9%). The subgroup of antidepressants most frequently dispensed was selective serotonin reuptake inhibitors (SSRIs) (33%), followed by the sedative antidepressants mianserin and mirtazapin (22%) and tricyclic antidepressants (TCAs) (20%). Except for TCAs, prescriptions of all antidepressant subgroups were reimbursed for either anxiety or depression in 90% of the cases. Overall, 46.9% of the antidepressant users were prescribed antidepressants in the category < 1 DDD per day and/or treatment < 3 months, with no gender difference. Conclusions: About one out of five OMT-patients filled a prescription for an antidepressant drug in 2009. Above 90% had their prescriptions reimbursed for either depression or anxiety. Use at low doses and/or sporadic use among half of the antidepressant users may reflect poor compliance or use for other maladies than the reimbursed disease code. Drug therapy for depression and anxiety among OMT-patients seems to be in line with recommendations for use; the SSRIs constitute the recommended drugs of choice due to their better effect/side effect profile, compared to the older antidepressants such as the TCAs.