Risk factors contributing to a low darunavir plasma concentration.

Darunavir is an efficacious drug; however, pharmacokinetic variability has been reported. The objective of this study was to find predisposing factors for low darunavir plasma concentrations in patients starting the once- or twice-daily dosage. Darunavir plasma concentrations from January 2010 till December 2014 of human immunodeficiency virus-infected individuals treated in the outpatient clinic of the University Medical Center Groningen were retrospectively reviewed. The first darunavir plasma concentration of patients within 8 weeks after initiation of darunavir therapy was selected. A dichotomous logistic regression analysis was conducted to select the set of variables best predicting a darunavir concentration below median population pharmacokinetic curve. In total 113 patients were included. The variables best predicting a darunavir concentration besides food intake included age together with estimated glomerular filtration rate (Hosmer-Lemeshow test P = 0.945, Nagelkerke R  = 0.284). Systematic evaluation of therapeutic drug monitoring results may help to identify patients at risk for low drug exposure.