Potentially inappropriate prescribing in Canada relative to the US

To explore the prescribing of potentially inappropriate drug therapy in Ontario, Canada where there is a restrictive drug formulary relative to the US where there is no single drug formulary.

A retrospective, cohort study using an administrative database (Ontario, Canada) compared with published survey results (US). All 1,088,680 community-dwelling adults >or=66 years of age in Ontario, Canada compared with published survey results from 2455 community-dwelling older adults in the US in 1996. Patterns of potentially inappropriate drug prescribing were compared between countries using a list of 33 potentially inappropriate drug therapies. These therapies were classified by an expert panel into three categories: (i) those to always avoid; (ii) those which are rarely appropriate; and (iii) those with only some indications to prescribe.

Among the 33 potentially inappropriate drug therapies, 15 (45%) prescribed in the US were not available through Ontario's drug formulary. Potentially inappropriate drug therapies available through the Ontario Drug Benefit Plan (ODB) and also in the US were frequently prescribed in both Ontario and the US. Differences in prescribing patterns of individual drug therapies were noted between the two countries. Specifically, in the rarely appropriate category, diazepam, a long half-life benzodiazepine, was much more frequently dispensed in Ontario than in the US (3.18% vs 1.37%). In contrast, dextropropoxyphene, an opioid with a poor adverse event profile was more frequently prescribed in the US than in Ontario (6.21% vs 0.74%).

Almost half of the potentially inappropriate drug therapies that are available in the US are unavailable from Ontario's drug formulary. Potentially inappropriate drug therapies that were available through the ODB were frequently prescribed in both countries. Alternative approaches that make information immediately accessible to physicians at the time they make prescribing decisions should be considered to improve prescribing practices.