Chloride channel opening results in membrane hyperpolarization, which inhibits cellular excitation. Enhanced GABA neurotransmission results in sedation, striated muscle relaxation, anxiolysis, and anticonvulsant effects. GABA receptors may cause decreased cardiac contractility, vasodilation, and enhanced perfusion. The rate of onset of action of benzodiazepines is determined by their rate of absorption from the GI tract. The more lipophilic agents usually are absorbed more rapidly and produce a more rapid onset of effect.
Absorption occurs more rapidly with ethanol and an empty stomach.
Peak blood concentrations of most agents occur within 1-3 hours. Most benzodiazepines are broken down into pharmacologically active metabolites. These metabolites may have longer half-lives than the parent compounds. Mortality from a pure benzodiazepine overdose is rare. Mortality usually occurs in conjunction with concomitant alcohol use or use of other sedative-hypnotics.