Alprazolam 1.5 mg (SR) · Tablets

Alprazolam is a 1,4 benzodiazepine. Alprazolam exerts its effect for the treatment of panic disorder through binding to the benzodiazepine site of gamma-aminobutyric acid-A (GABAA) receptors in the brain and enhances GABA-mediated synaptic inhibition.

The pharmacokinetics of alprazolam and two of its major active metabolites (4-hydroxyalprazolam and α-hydroxyalprazolam) are linear, and concentrations are proportional up to 10 mg alprazolam extended-release tablets given once daily.

Absorption — Following oral administration of alprazolam extended-release tablets in the morning, peak plasma concentration of alprazolam (Cmax) occurs in about 10 hours postdose. Compared to morning dosing, alprazolam Cmax increased by 30% and the Tmax decreased by an hour following dosing at night.

The mean absolute bioavailability of alprazolam following administration of alprazolam extended-release tablets is approximately 90%, and the relative bioavailability compared to alprazolam is about 100%. The bioavailability and pharmacokinetics of alprazolam following administration of alprazolam extended-release tablets are similar to that for alprazolam, with the exception of a slower rate of absorption.

Effect of Food — A high-fat meal given up to 2 hours before dosing with alprazolam extended-release tablets increased the mean Cmax by about 25%. The effect of this meal on Tmax depended on the timing of the meal, with a reduction in Tmax by about 1/3 for subjects eating immediately before dosing and an increase in Tmax by about 1/3 for subjects eating 1 hour or more after dosing. The extent of exposure (AUC) and elimination half-life (t1/2) were not affected by eating.

Distribution — The apparent volume of distribution of alprazolam is similar for alprazolam extended-release tablets and alprazolam. Alprazolam is 80% bound to human serum protein, and albumin accounts for the majority of the binding.

Elimination — The mean plasma elimination half-life of alprazolam following administration of alprazolam extended-release tablets ranges from 10.7 to 15.8 hours in healthy adults.

Metabolism — Alprazolam is extensively metabolized in humans, primarily by cytochrome P450 3A4 (CYP3A4), to two major active metabolites in the plasma: 4-hydroxyalprazolam and α-hydroxyalprazolam. The plasma circulation levels of the two active metabolites after both alprazolam extended-release tablets and alprazolam are less than 10% and 4% of the parent, respectively. The reported relative potencies in benzodiazepine receptor binding experiments and in animal models of induced seizure inhibition are 0.20 and 0.66, respectively, for 4-hydroxyalprazolam and α-hydroxyalprazolam. The low concentrations and low potencies of 4-hydroxyalprazolam and α-hydroxyalprazolam indicate that they unlikely contribute much to the effects of alprazolam. A benzophenone derived from alprazolam is also found in humans. Their half-lives appear to be similar to that of alprazolam. The pharmacokinetic parameters at steady-state for the two hydroxylated metabolites of alprazolam (4-hydroxyalprazolam and α-hydroxyalprazolam) were similar for alprazolam and alprazolam extended-release tablets, indicating that the metabolism of alprazolam is not affected by absorption rate.

Excretion — Alprazolam and its metabolites are excreted primarily in the urine.

Geriatric Patients — The mean T1/2 of alprazolam was 16.3 hours (range: 9.0 to 26.9 hours) in healthy elderly subjects compared to 11.0 hours (range: 6.3 to -15.8 hours, n=16) in healthy adult subjects.

Obese Patients — The mean T1/2 of alprazolam was 21.8 hours (range: 9.9 to 40.4 hours) in a group of obese subjects.

Patients with Hepatic Impairment — The mean T1/2 of alprazolam was 19.7 hours (range: 5.8 to 65.3 hours) in patients with alcoholic liver disease.

Racial or Ethnic Groups — Maximal concentrations and T1/2 of alprazolam are approximately 15% and 25% higher in Asians compared to Caucasians.

Smoking — Alprazolam concentrations may be reduced by up to 50% in smokers compared to non-smokers.

In Vivo Studies — Most of the interactions that have been documented with alprazolam are with drugs that modulate CYP3A4 activity.

Compounds that are inhibitors or inducers of CYP3A would be expected to increase or decrease plasma alprazolam concentrations, respectively. Drug products that have been studied in vivo, along with their effect on increasing alprazolam AUC, are as follows: ketoconazole, 3.98 fold; itraconazole, 2.66 fold; nefazodone, 1.98 fold; fluvoxamine, 1.96 fold; and erythromycin, 1.61 fold [see Contraindications (4), Warnings and Precautions (5.5), Drug Interactions (7.2)]. Other studied drugs include: