| Summary: | <h4>Objective</h4> <p>We aimed to characterise the effects of CYP2B6 polymorphisms, diurnal variation, and demographic factors on nevirapine pharmacokinetics in African children.</p> <h4>Methods</h4> <p>Nonlinear mixed-effects modelling conducted in NONMEM 7.3 described nevirapine plasma concentration-time data from 414 children aged 0.3–15 years. </p> <h4>Results</h4> <p>Nevirapine pharmacokinetics was best described using a 1-compartmental disposition model with elimination through a well-stirred liver model accounting for first-pass effect and transit-compartment absorption. Intrinsic clearance was affected by diurnal variation (characterised using a cosine function with peak amplitude 29% at 12 noon) and CYP2B6 metaboliser status (extensive [EM] 516GG|983TT, reference; intermediate [IM] 516GT|983TT or 516GG|983TC, 17% lower; slow [SM] 516TT|983TT or 516GT|983TC, 50% lower; ultra-slow [USM] 516GG|983CC, 68% lower). Age was found to affect pre-hepatic bioavailability: 31.7% lower at birth and increasing exponentially. Median (90% CI) evening Cmin in the different metaboliser groups were 5.01 (3.01-7.47), 6.55 (3.65-13.32), 11.59 (5.44-22.71), and 12.32 (12.32-27.25) mg/L, respectively. Evening Cmin were <3mg/L in 43% of EM <6kg and 26% of IM <6kg, while 73% of SM and 88% USM in all weight-bands had evening Cmin >8 mg/L. Cmin was not markedly affected by administration time but by unequal splitting of the daily dose.</p> <h4>Conclusions</h4> <p>Diurnal variation does not greatly affect nevirapine exposure. However, when daily doses cannot be split equally, the larger dose should be given in the morning. To achieve homogeneous exposures, nevirapine doses for SM and USM should be reduced by 50%, and children <6kg with EM or IM metabolizer status should receive the same dose as children weighing 6-10 kg.</p>
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