A retrospective analysis of potential drug interactions of antiretroviral prescriptions in a section of the private health care sector of South Africa

Abstract

There was a decrease in the percentage of DDls between ARVs and other drugs (clinical significance level 1) for 2005 as compared to 2004 due to the possible impact of PMBs on HN/AIDS implemented in South Africa in 2005. However there was an increase in possible DDIs between ARVs interacting with each other at clinical significance level 2 for year 2005 as compared to year 2004. This was due to implementation of prescribed minimum benefits (PMB) for HN/AIDS with many medical schemes contracted, registering more HN/AIDS patients resulting in the increase in the number of ARV prescriptions and therefore DDIs between them. Furthermore potential DDIs were identified between ARVs themselves, mostly the non-nucleoside reverse transcriptase inhibitors like efavirenz and protease inhibitors like ritonavir. Among the protease inhibitors, ritonavir presented with the highest prevalence of prescriptions with potential DDIs all interacting at clinical significance level 2 with saquinavir, indinavir and nevirapine. The highest prevalence of ARV prescriptions with highest potential for DDls identified, in database B, between ARVs (clinical significance level 2) was in triple-therapy combinations for years 2005 and 2006 and in dual-therapy for year 2007 in database B. The results reveal that monotherapy still existed in this section of the private health care sector. Potential DDIs identified between ARVs with prescribed daily doses (PDDs) not according to the recommended ARV dosing, were mostly in combinations of lopinavir/ritonavir (protease inhibitors) at PDD of799.8 mg/198 mg and efavirenz (EFV) 600 mg, followed by indinavir (IND) (protease inhibitors) 1600 mg and ritonavir (RTV) (protease inhibitors) 200 mg, then RTV 200 mg and EFV 600 mg. The prevalence of ARV prescription with potential DDls between ARVs and with prescribed daily doses not according to the recommended ARV dosing increased from 2005 to 2007 for both general practitioners CGPs) and specialists CSPs) prescriptions. Identified regimens with DDls and prescribed daily doses not according to the recommended ARV dosing were between lopinavir/ritonavir at prescribed daily doses 1066.4 mg/264 mg and efuvirenz at PDD 600 mg being higher in GP as compared to SP prescriptions. These regimens were mostly prescribed to patients in the age group older than 19 to 45 years for the three years. The clinical relevance of the identified potential DDIs was evaluated according to criteria stated in the literature. No clinical evaluation of the real effects of these interactions was possible. However, the results emphasised the possibility of the potential DDIs that could have led to severe problems in this section of the private health care sector in South Africa. It is recommended that the management of these potential DDIs between ARVs in clinical practice be done in accordance with the recommended treatment guidelines. Recommendations regarding further studies were formulated.