When a patient is already receiving a continuous IV infusion, measuring the parent drug in blood ordinarily blends that exposure with any oral dose. A labeled tracer can distinguish the oral contribution.
Investigators gave a single oral carbon-14 midazolam microtracer to 46 clinically stable children in intensive care who were receiving therapeutic IV midazolam. The label allowed the team to follow the tracer separately. Their model estimated typical oral bioavailability at 66%, with individual estimates ranging from 25% to 85%. The study also measured the hydroxylated and glucuronidated metabolites.
Bioavailability estimates how much of the oral dose reaches the circulation. It is distinct from how quickly the body clears midazolam once it is there. The population estimate and wide range describe this study’s patients. An individual interpretation needs the actual route, dose history and specimen timing.
Population pharmacokinetic study of midazolam oral bioavailability in critically ill children (full text) · DOI