A study of pharmacokinetic interaction between buspirone and alprazolam at steady state

The steady-state pharmacokinetic interaction between buspirone and alprazolam was evaluated in a parallel study with two groups of 12 male volunteers each. On days 1 to 7, group I subjects received a 1-mg alprazolam tablet every 8 hours (q8h) (TRT 1) and group II subjects received 2 x 5-mg buspirone tablets q8h (TRT 2). On days 8 through 14, all subjects received a combination of 1-mg alprazolam and 2 x 5-mg buspirone tablets q8h (TRT 3). Plasma samples, collected 0 to 8 hours after the morning dose on days 7 and 14, were analyzed for buspirone, alprazolam and their metabolites, 1-PP, and alpha-HO-alprazolam, respectively. Additional samples were collected before the morning dose on days 5 and 6 of each session to monitor the attainment of steady state. Steady-state pharmacokinetic parameters Cmax, Tmax, AUC0-8, and Cmin were calculated. The results indicated that for alprazolam, there was a small (< 10%) increase in Cmax and AUC when coadministered with buspirone. For buspirone, there was a 10% and 29% increase in Cmax and AUC, when coadministered with alprazolam. These values were within the normal variability observed with this class of drugs. Except for a 14% decrease in Cmin for alpha-HO-alprazolam, coadministration of buspirone and alprazolam did not affect the parameters for the metabolites. The results of this study suggest that coadministration of buspirone and alprazolam did not markedly affect the steady-state pharmacokinetics of either drug.