Midazolam

Midazolam is the most commonly used parenteral sedative in anaesthetic practice. The structure of midazolam is altered by local changes in pH (tautomerism), and the two different forms confer either water or lipid solubility to the drug . At pH<4 the benzodiazepine nucleus opens because of an ionisable amine group in the molecule's structure, and this increases water solubility. At plasma pH the amine group is incorporated back into the unionised ring form of the molecule, which is highly lipid soluble and diffuses rapidly into the brain. A concentrated preparation (5mgml 1 ) is available for i.m. injection and absorption is rapid compared with diazepam.