The dose chart and the plasma result describe different parts of midazolam exposure. In a prospective ICU study, patients receiving venovenous extracorporeal membrane oxygenation (ECMO) received more midazolam by weight than patients on conventional respiratory support. The concentration results did not follow the same pattern for the parent drug and its metabolites.
The study included 14 ECMO patients and 11 comparison patients. Mean daily weight-adjusted dosing was about 3.6 versus 1.8 mg/kg. The authors found no statistically significant difference in parent midazolam concentrations and reported higher α-hydroxymidazolam concentrations in the ECMO group.
The authors summarized repeat samples at the patient level, so 132 measurements represented 25 patients. The groups also differed in body mass index. The findings show why dose alone is a poor substitute for measured concentrations. The study did not isolate how much of the difference came from the circuit, the patients’ illnesses, or other factors.