Lorazepam pharmacology
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Lorazepam Absorption, Distribution, Metabolism, and Excretion
Lorazepam is a 3-hydroxy, 1,4-benzodiazepine that is rapidly and readily absorbed after oral administration, reaching peak blood concentrations about two hours post-dose. Its elimination half-life is approximately 12 hours in adults, with steady-state blood levels achieved within 2–3 days of repeated dosing. Lorazepam is primarily metabolized in the liver by conjugation with glucuronic acid to form an inactive glucuronide, which is then excreted in the urine. About 70–75% of the administered dose is recovered as the glucuronide conjugate in urine, and both the active drug and its metabolite are eliminated from the blood within a week after the last dose . In infants and children, lorazepam is also well absorbed, but the elimination half-life is longer—about 15 hours in healthy children and up to 24–37 hours in those with severe illness .
Mechanism of Action and Pharmacodynamics
Lorazepam acts as an allosteric agonist at the GABA_A receptor, enhancing the inhibitory effects of GABA in the central nervous system. This results in anxiolytic, sedative, anticonvulsant, and muscle relaxant properties. Animal studies show that lorazepam reduces anxiety-related behaviors, inhibits convulsions, and suppresses aggressive responses at lower doses compared to other benzodiazepines, indicating high potency as an anxiolytic agent . In humans, lorazepam is more potent than midazolam for sedation, with a sedative potency approximately twice that of midazolam and a relative amnestic potency four times greater. However, lorazepam is associated with longer emergence times from sedation, especially after prolonged infusions in critically ill patients .
Drug Interactions and Genetic Factors
Lorazepam can interact with other drugs, potentially affecting its activity or metabolism. For example, when combined with thiopentone, lorazepam enhances the hypnotic effects beyond simple addition, but does not significantly alter the effects of skeletal neuromuscular blocking drugs . Genetic polymorphisms, particularly in the UGT2B7 and UGT2B15 enzymes responsible for glucuronidation, may influence the pharmacodynamic interaction between lorazepam and other drugs like valproic acid, although effects on pharmacokinetics are less pronounced .
Effects on the Central Nervous System
Lorazepam administration leads to decreased cortical excitability and increased GABA_A receptor-mediated inhibition, as shown by transcranial magnetic stimulation and magnetic resonance spectroscopy studies. It decreases GABA levels in the occipital cortex and increases short intracortical inhibition, reflecting its action on synaptic GABAergic activity . Lorazepam also impairs memory performance and reduces activation in brain regions involved in memory encoding, such as the hippocampus and fusiform gyrus . Additionally, lorazepam can modulate emotional processing and moral decision-making, influencing choices in moral dilemmas by downregulating negative emotionality .
Clinical Use and Safety in Special Populations
Lorazepam is effective and generally safe for use in infants and children, with dosing adjusted for age and route of administration. It is used for its antiepileptic activity and can be administered intravenously, orally, or via other routes. Lorazepam crosses the placenta freely but has limited transfer into breast milk . In animal models of diabetic peripheral neuropathy, lorazepam has shown potential to reduce neuroinflammation by suppressing T cell infiltration and modulating inflammatory pathways .
Conclusion
Lorazepam is a potent benzodiazepine with rapid absorption, predictable metabolism via glucuronidation, and strong anxiolytic, sedative, and anticonvulsant effects. Its pharmacological profile is influenced by genetic factors, drug interactions, and patient characteristics such as age and illness. Lorazepam’s effects on the central nervous system include enhanced GABAergic inhibition, memory impairment, and modulation of emotional and moral processing. It remains a valuable therapeutic agent in both adult and pediatric populations, with ongoing research into its broader pharmacological actions.
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