Determining potential drug-drug interactions between lopinavir/ritonavir and other antiretrovirals and prescribed daily doses in a section of the private health care sector in South Africa

Lopinavir/ritonavir forms part of the antiretroviral therapy for the treatment of human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS). The aim of this non-experimental, quantitative drug-utilization study was to determine and identify potential drug-drug interactions between lopinavir/ritonavir and other antiretrovirals in general practitioners and specialists prescriptions with inappropriate prescribed daily doses. The study was performed on 49,995 (2005), 81,096 (2006) and 88,988 (2007) anti-retroviral (ARV) prescriptions claimed through a pharmacy benefit management company. Of the total 2,638 ARV general practitioners prescriptions and 472 specialist’s prescriptions claimed with potential drug-drug interactions (DDIs), 505 (19.1%) were for general practitioners and 143 (30.3%) for specialists. Potential drug-drug interactions identified between lopinavir/ritonavir and other anti-retrovirals with inappropriate prescribed daily doses accounted for 88.9% (n = 449) for general practitioners and 98.6% (n = 141) for specialist’s prescriptions. The highest percentage of anti-retroviral prescriptions with potential drug-drug interactions were between lopinavir/ritonavir at 1066.4 mg/264 mg and efavirenz at 600 mg average of prescribed daily doses with 61.4% (n = 276) for general practitioners and 38.3% (n = 54) for specialists, prescribed to patients between 19 and 45 years. The recommended standard adult dose for lopivavir/ritonavir is 400 mg/100 mg twice daily or 800 mg/200 mg once daily. The dose prescribed to HIV/AIDS patients in this section of the private health care sector of South Africa was therefore high. It is therefore recommended that more education be given to prescribers and dosage adjustments be done where indicated.