As a benzodiazepine, alprazolam produces a variety of therapeutic and adverse effects by binding to and modulating the function of the GABAA benzodiazepine receptor site; benzodiazepines are thus so-called allosteric modulators. GABA receptors are the major inhibitory receptors in the brain. Binding of alprazolam to the GABAA receptor, a chloride ion channel, enhances the action of GABA gammaaminobutyric acid), a neurotransmitter. When GABA binds to the GABAA receptor, the channel opens and chloride enters the cell, making it more resistant to depolarization (impulse for transmission of the nerve stimulus). Therefore, alprazolam has a depressant effect on synaptic transmission to reduce anxiety.
Alprazolam is taken orally and absorbed rapidly in the intestine - 80% of alprazolam binds to proteins in serum (mainly albumin). The concentration (Cmax ) of alprazolam peaks after one to two hours. Alprazolam is metabolized in the liver, primarily by the enzyme cytochrome P450 3A4 (CYP3A4). Two major metabolites are formed: 4-hydroxyalprazolam and α-hydroxyalprazolam, as well as an inactive metabolite. The low concentrations and low potencies of 4-hydroxyalprazolam and α-hydroxyalprazolam suggest that they make little to no contribution to the effects of alprazolam. The metabolites and some of the unmetabolized alprazolam are filtered out by the kidneys and excreted in the urine. The plasma half-life is approximately 11.2 hours, although this value may vary widely depending on the renal function of the patient.
It is metabolized primarily by CYP3As and is therefore contraindicated with CYP3A inhibitors such as cimetidine, erythromycin, norfluoxetine, fluvoxamine, itraconazole, ketoconazole, nefazodone, propoxyphene, and ritonavir, as these may lead to accumulation of alprazolam and a greater number of serious adverse effects.
It has been reported that plasma concentrations of imipramine and desipramine may increase with concomitant administration of alprazolam tablets. Combined oral contraceptive pills reduce the clearance of alprazolam, which may result in increased plasma levels of alprazolam.
Alcohol and alprazolam taken in combination have a synergistic effect on each other, which can lead to severe sedation, behavioral changes, and intoxication. The more alcohol and alprazolam taken, the worse the interaction. This type of abuse is often found in the party scene.