ABSTRACT
Background: The introduction of human immunodeficiency virus (HIV) protease inhibitors (PIs) has led to a dramatic decline in the morbidity and mortality associated with HIV infection. However; the concomitant use of PIs and other antiretrovirals (ARVs) can be complicated by drug-drug interactions (DDIs); adversely affecting levels of PIs. Methods: A quantitative; retrospective drug utilisation study was performed using data obtained from the medicine claims database of a pharmacy benefit management company during 2004; 2005 and 2006. The possible DDIs found among ARVS themselves were identified using the classification by Tatro.Results: The percentage of ARV prescriptions claimed of the total number of medicine items increased from 1.68(n = 43 482) during 2004 to 3.18(n = 51 613) during 2005; then to 4.74(n = 47 085) during 2006. A total of 1 326; 1 863 and 960 possible DDIs were identified among ARVs themselves for 2004; 2005 and 2006 respectively. Of these; ritonavir (unboosted or boosted) presented with the most possible DDIs; accounting for 74.28(n = 985) for 2004; 67.90(n = 1 265) for 2005; and 27.50(n = 264) for 2006. The highest prevalence of DDIs identified was between ritonavir (unboosted) and saquinavir (n = 974; 5) for 2005 and 2006; followed by indinavir (n = 490; 129; 155) for 2004 to 2006; and efavirenz (n = 274) for only 2004; then ritonavir (boosted); co-formulated as lopinavir/ritonavir; and efavirenz (n = 118; 88; 34) for 2004 to 2006; nevirapine (n = 49; 37) for 2004 and 2005; indinavir (n = 9) for 2004; and saquinavir (n = 22) for 2006.Conclusion: These findings indicate that concomitant use of PIs such as ritonavir; a potent cytochrome P450(CYP)3A4 enzyme inhibitor; and other ARVs is complicated by possible DDIs and therefore further studies need to be done on the ARV combinations and management of these DDIs. How to cite this article: Katende-Kyenda; N.L.; Lubbe; M.S.; Serfontein; J.H.P.; Truter; I. 2009. Analysis of possible drug-drug interactions between ritonavir and other antiretrovirals in a section of the private health care sector in South Africa. African Journal of Primary Health Care et Family Medicine; 1(1); Art. #21; 6 pages. DOI: 10.4102/ phcfm.v1i1.21