Prevalence of possible drug-drug interactions between antiretroviral agents in different age groups in a section of the private health care sector setting in South Africa.

BACKGROUND: The chronic nature of human immunodeficiency virus (HIV) infection requires lifelong highly active antiretroviral (ARV) therapy (HAART) to continuously suppress HIV-1 viral replication, thus reducing morbidity and mortality. HAART is restricted by complex dosing, drug-drug interactions (DDIs) and toxicities.

OBJECTIVE: To determine the prevalence of possible DDIs between ARV drugs in different age groups in a section of the private primary health care sector in South Africa.

METHODS: A quantitative, retrospective drug utilization review was performed on 47 085 ARV prescriptions claimed through a national medicine claims database during 2006. Possible DDIs identified were classified according to a clinical significance rating as described by Tatro [Drug Interaction Facts 2005. St Louis, MO: Facts and Comparisons (2005)].

RESULTS: The total number of patients who received prescriptions that were claimed through the medicine claims database was 275 424, of whom 25.11% were males, 28.28% were females and the gender of 46.61% patients was unknown. Of the total number of patients, 3.27% were HIV patients of which an average of 5.23 +/- 3.86 ARV prescriptions (n = 47 085) per patient were claimed for representing 4.73% of the total number of prescriptions claimed during the study period (N = 993 804). HIV patients received an average of 2.36 +/- 0.61 ARVs per prescription. Only 4.95% of the prescriptions had one ARV medicine item, 56.04% two, 37.10% three, 1.75% four and <1% had more than four. Of 960 DDIs identified, 1.88% were for patients < or =6 years, 4.27% for patients >6 years and < or =12 years, 0.63% for patients >12 and < or =19 years, 32.40% for patients <19 years and < or =40 years, 60.21% for patients <40 years and < or =60 years and 0.63% for patients >60 years with patients <40 years and < or =60 years having the highest number of DDIs and patients older than 60 years the lowest. The majority of DDIs between the ARVs presented in significance levels 2 and 4. The most important interactions were between: indinavir (IDV) and ritonavir (n = 199); efavirenz (EFV) and lopinavir/ritonavir (n = 65) and EFV and IDV (n = 60) all interacting at level 2.

CONCLUSION: The importance of using drug utilization study as an identification tool to provide insight into the prescribing and utilization patterns of ARV drugs, to provide optimal therapy for patients infected with HIV is emphasized.