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 benzodiazepine onset of action is determined by rate of benzodiazepine absorption from the GI tract. The relatively lipophilic BZDs usually are absorbed more rapidly and produce a faster onset of effect than the relatively water-soluble BZDs.
Benzodiazepine absorption is especially rapid when ethanol is present and the stomach is empty.
Peak blood concentrations of most agents occur within 1-3 hours. Most benzodiazepines are broken down into pharmacologically active metabolites, which may have longer half-lives than the parent compounds. Elderly individuals and very young persons are more susceptible to the CNS depressant effects of benzodiazepines than people in other age groups. Intravenous administration is associated with greater degrees of hypotension than other routes of administration and occasional cardiac and respiratory arrest. History should include the time, dose, and intent of the overdose.