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The current treatment for Human Immunodeficiency Virus (HIV) patients coinfected with malaria involves the coadministration of antimalarial and antiretroviral (ARV) drugs. The World Health Organization (WHO) recommends artemisinin-based therapy for malaria that usually consists of artemether, artesunate or dihydroartemisinin with non-artemisinin derivatives such as amodiaquine, lumefantrine and mefloquine. Protease inhibitors (PI) such as ritonavir contribute to the improved health of HIV-positive individuals, and the inclusion of ritonavir in antiretroviral regimens is common in clinical practice. Ritonavir is a potent inhibitor of human CYP3A4, which is the primary enzyme involved in the metabolism of many of artemisinin-based drugs, as well as amodiaquine and proguanil. Upon co-administration, ritonavir can potentially influence the metabolism and thus increase the systemic exposure of these drugs. In order to understand this pharmacokinetic (PK) drug interaction, the current work evaluated the effect of ritonavir (50 mg/kg orally) on the PK of antimalarial drug combinations in Sprague Dawley (SD) rats. When co-administered with ritonavir, the exposure (AUC) of the antimalarial drugs artemether, artesunate and proguanil was increased by approximately 3.5-fold. Correspondingly, peak plasma concentrations (Cmax) of these drugs increased as well. There was no apparent influence of ritonavir on the PK of lumefantrine, amodiaquine and atovaquone. This study demonstrates the potential influence of ritonavir on the pharmacokinetics of at least some anti-malarial drugs, likely a result of inhibition of CYP3A. Further evaluation of clinically relevant drug interaction in humans may be warranted to ensure safe and effective use of anti-malarial and anti-HIV drugs concomitantly.
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