Examining the adequacy of quantities available for subsidized antidepressant prescriptions in Australia

In Australia the Pharmaceutical Benefits Scheme (PBS), a national drug insurance plan, aims to provide around a month's therapy for medication used in chronic conditions. However, there are marked differences among the most commonly used antidepressants in the number of days supply represented by the PBS maximum quantity after adjustment for the defined daily dose (DDD). The DDD is the assumed adult daily dose for a drug and is a WHO drug utilization standard. Whereas the selective serotonin re-uptake inhibitors (SSRIs) and moclobemide largely provide around a months supply at the DDD, most tricyclic antidepressant (TCA) items provide considerably less than this. A patient tracking study was conducted to determine the average length of time between prescription re-supplies for a number of tricyclic antidepressants and newer antidepressants as a means of measuring the efficiency of PBS supply for the different classes of antidepressant. The number of days between dispensings was similar for patients no matter whether they were taking TCAs, SSRIs or moclobemide, although for the older antidepressants presumably at a much lower prescribed daily dose than the DDD. Care needs to be taken when adjusting usage with the DDD/1000/day unit of measurement in cases where the DDD does not reflect the prescribed daily dose (PDD).