Co-prescribing of SSRIs and TCAs in Australia: how often does it occur andwho is doing it?

Aims To determine the frequency with which the selective serotonin re-uptak e inhibitor (SSRI) antidepressants are used as add-on therapy to the tricyc lic antidepressants (TCA) rather than as replacement therapy. Methods The data analysed were profiles of prescription records by date of supply to the patient. From within the national administrative dispensing c laims database, the subset eligible for social security entitlements was id entified as individuals by means of their coded permanent identification nu mbers (PINs). Following the initial supply of an SSRI in January 1996, the subsequent 6 months dispensing of SSRI and TCA antidepressants to these ind ividuals was examined. The main outcome measure was the proportion of indiv iduals to whom SSRIs and TCAs were dispensed concurrently, as an indirect m easure of coprescription. In instances where a patient was receiving prescr iptions for SSRIs and TCAs that had been written by the one doctor only, th e major specialty of the doctor was investigated. Results 55 271 PINs were dispensed 63 865 SSRI prescriptions in January 199 6 which represented over half (52%) of the total community SSRI prescriptio ns dispensed in chat month. The number of these patients meeting the criter ia for coprescription of SSRIs and TCAs over the next 6 months was 2773 (5% ). The coprescribing instances were highest in Queensland and the prescribe rs most frequently involved had psychiatry major specialty codes. Conclusions Among SSRI users there is a cohort of patients who, within the same time frame, are receiving supplies of a TCA, the nonselective drug tha t the SSRIs were designed to replace. This is indirect evidence of probable coprescription. Such combination use is of uncertain clinical and cost eff ectiveness, and carries additional risks. The SSRIs were included on the su bsidy list in Australia on the basis of reasonable cost effectiveness as mo notherapy compared with the TCAs. Our data imply that for some patients, an tidepressant prescribing is inconsistent with the basis on which government subsidy was approved.