Quazepam
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Mechanism of action
Like other benzodiazepines, quazepam likely exerts its effects by potentiating the effect of gamma-aminobutyric acid (GABA) on GABA(A) receptors, the main inhibitory neurotransmitter receptors in the mammalian brain. GABA(A) receptors are a component of GABA-gated ionotropic chloride channels that produce inhibitory postsynaptic potentials - following activation by GABA, the channel undergoes a conformational change that allows the passage of chloride ions through the channel. The inhibitory potentials produced by GABA neurotransmission play an integral role in the suppression and control of epileptiform nerve firing such as that seen in epilepsy, which makes the GABA system a desirable target in the treatment of epilepsy. Benzodiazepines are positive allosteric modulators of GABA(A) function. They bind to the interface between alpha (α) and gamma (γ) subunits on the receptor, commonly referred to as the benzodiazepine binding site, and modulate the receptor such that its inhibitory response to GABA binding is dramatically increased.
Pharmacodynamics
Benzodiazepines, including quazepam, exert their sedative and anxiolytic effects by potentiating the effects of endogenous GABA, the primary inhibitory neurotransmitter in the central nervous system.
Pharmacokinetics
Half-life
The mean elimination half-lives of both quazepam and 2-oxoquazepam is approximately 39 hours. The mean elimination half-life of N-desalkyl-2-oxoquazepam is approximately 73 hours.
Absorption
The half-life of absorption following oral administration is approximately 30 minutes. Peak plasma concentration (Cmax) is approximately 20 ng/mL and occurs around 2 hours following administration.
Over the course of five days following the administration of radiolabeled quazepam, approximately 31% of the administered dose appeared in the urine and 23% appeared in the feces. Unchanged drug appeared in only trace amounts in the urine.
Metabolism
Quazepam undergoes extensive hepatic metabolism, primarily via CYP3A4 and to a lesser extent via CYP2C9, CYP2C19, and FMO1. Quazepam is first metabolized to 2-oxoquazepam, which is then further metabolized to both N-desalkyl-2-oxoquazepam (norflurazepam) and 3-hydroxy-2-oxoquazepam. Both 2-oxoquazepam and N-desalkyl-2-oxoquazepam exert CNS depressant activity.
Quazepam has known human metabolites that include 2-oxoquazepam.
Hepatic.
Half Life: 39 hours
Protein binding
Quazepam and both of its major metabolites are >95% protein-bound in plasma.
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