The study population consisted of predominantly female patients with normal baseline clinical chemistry and haematology. Although a very small

proportion of patients had subtherapeutic efavirenz concentrations, autoinduction was associated with lower steady-state efavirenz concentration in plasma. More than half of the patients experienced efavirenz-related CNS toxicity, with a higher frequency of moderate and severe symptoms among patients who had higher efavirenz plasma concentrations in samples taken at least 8 h after day-14 dosing. The mean minimum and maximum concentrations of efavirenz observed at steady state (4.1 and 7.4 µg/mL, respectively) were higher than those reported in initial efavirenz studies BMS-354825 mouse [22–24] but consistent with those reported in African populations [3,4]. The finding that more than half of the efavirenz plasma concentrations were above the therapeutic range is similar to findings obtained in Zimbabwe [4] and, although an analysis of the effect of CYP polymorphisms was not within the scope of this study, the high frequency of elevated efavirenz plasma concentrations is likely to be related to the high frequency of CYP2B polymorphism in African populations [4,7]. This study further showed that nearly all the HIV-infected Ugandans on efavirenz experienced toxic efavirenz levels everyday, indicating that dosage

adjustments previously suggested for Africa [4] Sirolimus may be required to reduce

efavirenz toxicity. The failure to find a significant influence of gender on efavirenz exposure, although such an influence has previously been reported [4,7], may have been a result of the skewed gender balance, as there were twice as many female as male participants. The effect of total bilirubin on efavirenz exposure previously reported [16] was not observed in this study; however, such a failure to observe any effect of parameters related to liver function has been documented before, and has been found in HIV-infected patients coinfected with hepatitis [25,26]. The results Glutamate dehydrogenase of this study showed plasma albumin concentration to be a significant covariate, with low plasma albumin correlating with high AUC and Cmax, and this could be related to the fact that efavirenz is known to be >99% protein bound, with albumin being the main protein to which efavirenz binds [1,35]. Although there are insufficient data in the literature to explain this finding, and the method of analysis for plasma efavirenz concentration applied in this study does not distinguish between bound and unbound efavirenz, the possible implications of such a finding have been discussed previously. Almond et al. observed a direct relationship between the percentage of bound efavirenz in plasma and the intracellular accumulation of efavirenz [27]. He concluded that the intracellular accumulation of efavirenz was related to its binding to intracellular proteins [27].