Impact of the introduction of mandatory generic substitution in South Africa: private sector sales of generic and originator medicines for chronic diseases.

Objective: To assess the impact of mandatory offer of generic substitution, introduced in South Africa in May 2003, on private sector sales of generic and originator medicines for chronic diseases.

Methods: Private sector sales data (June 2001 to May 2005) were obtained from IMS Health for proton pump inhibitors (PPIs; ATC code A02BC), HMG-CoA reductase inhibitors (statins; C10AA), dihydropyridine calcium antagonists (C08CA), angiotensin-converting enzyme inhibitors (ACE-I; C09AA) and selective serotonin reuptake inhibitors (SSRIs; N06AB). Monthly sales were expressed as defined daily doses per 1000 insured population per month (DDD/TIM). Interrupted time-series models were used to estimate the changes in slope and level of medicines use after the policy change. ARIMA models were used to correct for autocorrelation and stationarity.

Results: Only the SSRIs saw a significant rise in level of generic utilisation (0.2 DDD/TIM; P < 0.001) and a fall in originator usage (-0.1 DDD/TIM; P < 0.001) after the policy change. Utilisation of generic PPIs fell (level 0.06 DDD/TIM, P = 0.048; slope 0.01 DDD/TIM, P = 0.043), but utilisation of originator products also grew (level 0.05 DDD/TIM, P < 0.001; slope 0.003, P = 0.001). Generic calcium antagonists and ACE-I showed an increase in slope (0.01 DDD/TIM, P = 0.016; 0.02 DDD/TIM, P < 0.001), while the originators showed a decrease in slope (-0.003 DDD/TIM, P = 0.046; -0.01 DDD/TIM, P < 0.001). There were insufficient data on generic statin use before the policy change to allow for analysis.

Conclusion: The mandatory offer of generic substitution appeared to have had a quantifiable effect on utilisation patterns in the 2 years after May 2003. Managed care interventions that were already in place before the intervention may have blunted the extent of the changes seen in this period. Generic policies are an important enabling provision for cost-containment efforts. However, decisions taken outside of official policy may anticipate or differ from that policy, with important consequences.