A genotype can help frame a pharmacokinetic question. To explain a concentration from one critically ill child, an analyst also needs the conditions under which that concentration was measured.
The investigators genotyped 72 samples and examined relationships between CYP variants and midazolam pharmacokinetics. They reported an association between the CYP3A5 rs776746 grouping and lower measured plasma midazolam concentrations in a subgroup of children aged five or younger. They also presented analyses stratified by sex. The comparisons are subgroup findings from critically ill children, with small numbers for some genotype groups.
Start with the administered dose, the time of sampling, the assay reporting limit and the patient’s illness and co-medication timeline. A low reported concentration can have several explanations, and an analytical result near the reporting limit deserves attention before making a metabolic inference. The paper can support investigating a genotype association. It does not give a rule for back-calculating an individual child’s dose or degree of sedation.