Influence of Acetaminophen on Pharmacokinetics and Pharmacodynamics of Midazolam in Healthy Volunteers

Background: Midazolam and acetaminophen are often co-administered in anesthesia practice. Both are metabolized by CYP 3A4 enzyme in the liver, and hence compete for the enzyme sites. This might lead to reduced metabolic breakdown and enhanced pharmacodynamic effects of midazolam in the presence of acetaminophen. Methods: The present study was undertaken to test this hypothesis. After IRB approval from Mount Sinai Medical Center, 15 healthy volunteers were used for 2 tests. For the first test, they were randomly assigned to receive oral doses of either midazolam 0.3 mg/kg in cherry syrup (Protocol A), or midazolam 0.3 mg/kg plus cherry flavored acetaminophen 15 mg/kg (Protocol B). At set intervals from 0 to 480 min, the blood levels of midazolam and the subjects pulse rate, mean arterial pressure, respiratory rate, BIS index, and OAA/S scores were determined. After 2 weeks, the same subjects underwent the second test; they received the other medication protocol. Results: Acetaminophen slightly, but not significantly, increased the half life of blood midazolam, and the depressive effects of midazolam on the clinical signs of the subjects. Conclusion: These results lead us to conclude that there is no need to reduce the doses of midazolam when used in combination with acetaminophen.