Procedures
vomiting, renal or liver diseases, diarrhea
DRUG INTERACTIONS, BLOOD, SEVERE MALNUTRITION
Children with illnesses that could affect pharmacokinetic results, including severe diarrhea, vomiting, renal or liver diseases, and severe malnutrition, and those on concomitant medication known to cause drug–drug interactions with the drugs in the treatment regimen were not eligible. Children were on at least 6 weeks of trial treatment to achieve steady-state plasma concentrations before the 24-hour pharmacokinetic profiles were taken. We took blood samples predose and at 0.5, 1, 2, 4, 6, 8, 12, and 24 hours after observed intake of trial medication with a 250-kcal breakfast. The 0.5-hour sample was added in an amendment to the protocol and was therefore not available for all children. Blood sample volumes were within blood draw limits for children established for research studies [Blood samples were refrigerated within 10 minutes and centrifuged within 1 hour after collection. Plasma was separated and stored at −80°C until shipping to the central laboratory site for quantification. TAF and TFV plasma concentrations were measured at the Division of Clinical Pharmacology, University of Cape Town, South Africa. TAF and TFV were measured simultaneously using a validated and highly sensitive liquid chromatography–tandem mass spectrometry bioanalytical quantification method with a lower limit of quantification of 0.500 ng/mL for both TAF and TFV. The concentration of the analyte found devided by the known concentration of the analyte expressed as a percentage is the accuracy. The combined accuracy of the limit of quantification in low-, medium-, and high-quality controls of TAF and TFV was between 93.8% and 105.1%, with precision (coefficient of variation [%CV]) <13%.