Plasma and intracellular concentrations of antiretrovirals are critical determinants of antiviral activity and toxicity. US researchers conducted this study to assess concentrations of antiretrovirals in two much-used combinations in blood and peripheral blood mononuclear cells (PBMCs) of HIV-positive people 55 and older. The two combinations were tenofovir/emtricitabine plus efavirenz and tenofovir/emtricitabine plus atazanavir/ritonavir.
After study participants had taken the antiretrovirals long enough to ensure that they had reached steady-state concentrations, they gave blood samples at 11 points over a 24-hour period. The researchers determined 24-hour area under the concentration-time curves (AUC24h) and maximum concentrations (Cmax) for each antiretroviral. They compared these concentrations with those in historical controls from the general HIV population. None of the study participants met criteria for the frailty phenotype. Six people taking each regimen completed the study.
Compared with the general population, the 55-and-older study group had 8% to 13% lower plasma concentrations for tenofovir AUC24h and Cmax and 19% to 78% higher concentrations for emtricitabine and ritonavir AUC24h and Cmax.
Atazanavir AUC24h in plasma was 12% lower than in controls, while atazanavir Cmax was 9% higher. Efavirenz plasma AUC24h did not differ substantially from levels in controls, while efavirenz Cmax was 16% lower in the study group.
