Prevalence of drug-drug interactions of antiretroviral agents in the private health care sector in South Africa

Objectives. Human immunodeficiency virus (HIV) infection can be effectively treated with highly active antiretroviral therapy (HAART), requiring concomitant administration of three to four different agents, often with a high potential for drug-drug interactions (DDIs). This study aimed to determine the prevalence of possible DDIs between antiretrovirals (ARVs) themselves and other drugs. Design. Retrospective drug utilisation study using data from a national medicine claims database for the period 1 January to 31 December 2004. Setting. A section of the private health care sector in South Africa. Subjects. All ARV prescriptions (N=43 482) claimed during 2004. The possible DDIs found were classified according to a clinical significance rating described by Tatro (2005) in his book Drug Interaction Facts. Results. A total of 5 305 882 medicine items were prescribed; of these, 1.92% (N=101 938) were ARVs. Of the total number of 2 595 254 prescriptions, 1.68% (N=43 482) contained ARVs. A total number of 18 035 DDIs (81 different types) were identified; of these, 83.89% (N=15 130) were DDIs between ARVs and other drugs, while 16.11% (N=2 905) were DDIs between ARVs themselves. Possible DDIs with a clinical significance level of I (major, N=17) and 2 (moderate, N=1 436) represented 8.06% (N=1 453) of the total number of identified interactions. Conclusions. Since concomitant use of ARVs and other drugs used to treat HIV complications is increasing, there is a need to understand and anticipate these DDIs and to overcome them by dose adjustments and patient education, so that they are not life threatening to HIV/AIDS patients.