Generic substitution of commonly used medications: Australia-wide experience, 2007-2008

To study the extent of brand substitution and switching in three commonly used classes of drugs available on the Pharmaceutical Benefits Scheme (PBS).

Assessment of PBS claim records for a 1-year period from 1 August 2007 to 31 July 2008 for long-term concession cardholders drawn from a 10% random sample of the Australian population. The target drug classes were: statins (pravastatin, simvastatin), calcium channel blockers (CCBs) (amlodipine, felodipine, nifedipine), and selective serotonin reuptake inhibitor (SSRI) antidepressants (fluoxetine, fluvoxamine, paroxetine, sertraline).

Proportion of patients who were non-switchers (single brand only) and multiple switchers (two or more brand switches).

We retrieved information relating to 935 334 prescriptions for 122 000 patients. Of those patients filling at least four prescriptions for a product, 41 174 patients received statins, 27 230 received CCBs and 21 342 received SSRIs. More than half the patients received only one brand during the study period: 57% for statins, 60% for CCBs, and 63% for SSRIs. Multiple switching was recorded for 24% of patients with statins, 19% with CCBs, and 21% with SSRIs, with smaller proportions receiving three or more brands: 14% for statins, 10% for CCBs, and 12% for SSRIs. Multiple switching was more common among younger patients for all drug classes (28% for those aged < 50 years v 18% for those aged >/= 80 years).

Generic substitution with multiple switches is occurring in a small proportion of patients being treated with statins, CCBs or SSRIs. The potential for patient confusion appears to be relatively small, but this may change with recent incentives included in pharmacy reimbursement arrangements.