Midazolam: Bioavailability versus Route


Bioavailability of IM, rectal, and PO routes are 87, 18, and 27%, respectively. According to Smith’s Anesthesia (Chapter 7), “times for peak serum concentrations after intramuscular, rectal, and oral administration were 15, 30, and 53 minutes, respectively, whereas the drug clearance and bioavailability via these three different routes were 10.4, 50.8, and 33.4 mL/kg per minute and 87%, 18%, and 27%, respectively. The lower bioavailability after oral or rectal administration is consistent with the commonly used oral dose of 0.5 mg/kg, which is almost five times higher than intravenous dosing

Midazolam Timing: Peak Effect

  • Intravenous:
  • Intramuscular: 15 minutes (bioavailability 87%)
  • Rectal: 30 minutes (bioavailability 18%)
  • Oral: 53 minutes (although onset is in 10 minutes, bioavailability 27%)


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  1. K Payne, F J Mattheyse, D Liebenberg, T Dawes The pharmacokinetics of midazolam in paediatric patients. Eur. J. Clin. Pharmacol.: 1989, 37(3);267-72