Do Pharmacists Adhere to Brand Substitution Guidelines? The Example of Simvastatin

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ABSTRACTBackgroundAlthough pharmacists have been criticised for not following brand substitution guidelines, evidence is lacking. Brand substitution of simvastatin has been possible since November 2004 when the first generic became available; prior to this 2 non‐substitutable products were available.AimTo identify the rate of switching between brand and generic products of simvastatin.MethodAnalyses were conducted using Repatriation Pharmaceutical Benefits Scheme prescription claims data from 1 November 2002 to 28 February 2006. Switches were identified if different brand or generic products were dispensed consecutively. The change in the rate of switching post‐generics was compared to the pre‐generics baseline.ResultsFollowing introduction of generics the switching rate increased to 78.2 switches per 1000 dispensings. Switching was 22 times more likely post‐generics compared to pre‐generics (rate ratio 21.91 (20.01, 24.00), p < 0.001). The rate of switching did not change when 10 products were available for substitution compared to when there were only 4 (RR 1.02 (0.998, 1.041); p = 0.0664). Post‐generics, 64% of switches occurred when different prescriptions were dispensed consecutively.ConclusionSwitching between simvastatin products was low prior to generic availability, even though 2 products were available. The switching rate increased when bioequivalent products were available, suggesting that pharmacists practice in accordance with brand substitution legislation. Consumers were most vulnerable to switching when different prescriptions were dispensed consecutively. Pharmacists should be aware of this and take steps to ensure that switches do not occur unnecessarily.