Pharmacokinetics of diazepam during multiple dosing of a 6-mg controlled-release capsule once daily.

Sixteen subjects completed a two-way crossover study designed to determine the steady-state pharmacokinetic profiles of diazepam and desmethyldiazepam following a 6-mg controlled-release (CR) capsule dosed once daily compared with those of a 2-mg diazepam tablet dosed 3 times a day. Treatment A consisted of 14 days of CR dosing followed by 10 days of tablet dosing. Treatment B was the reverse of Treatment A. Plasma concentrations of diazepam and desmethyldiazepam were determined by an electron-capture gas-liquid chromatographic method. The areas under the diazepam plasma concentration-time curve were similar for both formulations at initiation of dosing and at steady-state, indicating comparable extents of absorption. The mean ratios of the areas at steady-state were near unity--0.94 for Treatment A and 0.91 for Treatment B--implying that no changes in steady-state conditions occurred upon switching regimens in either direction. The steady-state profiles of desmethyldiazepam were also comparable for the two dosage forms. These data indicate that the CR capsule and the conventional tablet t.i.d. produce similar target concentrations of both the drug and metabolite; therefore, these two dosage forms and dosing regimens should be interchangeable.

Pharmacokinetics of single and multiple ascending doses of the antiallergic agent tiacrilast in man.

Five groups of six healthy subjects received single oral doses of 150, 300, 450, 600 or 750 mg tiacrilast 150 mg capsules, followed 24 h later by the same dose given every 6 h for 7 days, in a study designed to assess the pharmacokinetics of single and multiple doses of tiacrilast. Plasma samples were obtained at specified times after the initial dose, after 4 days of multiple dosing and after the last dose of tiacrilast. Samples were assayed for unchanged drug by a specific HPLC method. Wide variability was seen in the plasma concentration-time data. Plasma concentrations and pharmacokinetic parameters were nearly proportional to dose over the 150 to 750 mg dose range studied. Moreover, there was no evidence of unexpected accumulation of the drug in the plasma during multiple dosing and food did not appear to alter the bioavailability of tiacrilast to any clinically significant extent. The apparent elimination half-life was similar after single and multiple doses and ranged from 1 to 3 h.