Radioreceptor assay of dopamine binding activity in human serum after tiospirone administration

Tiospirone has demonstrated preclinical activities that predict utility as an antipsychotic drug which lacks the potential to produce extrapyramidal side effects. Indeed, human safety trials after single and multiple dose administration did not reveal the presence of any neurological effects. Serum samples from these studies were obtained for radioreceptor assay to determine the level of dopamine binding activity present. After a single 75 mg dose of tiospirone, demonstrable levels of dopamine binding activity were present. A variety of time points were sampled during the multiple dose study wherein subjects received 60 mg, t.i.d. for 28 days. A comparison of levels of dopamine binding activity present in serum samples taken immediately prior to dosing on various days during the course of the study suggested that steady-state was achieved within seven days with repeated administration. No further rises were seen in the remainder of the study, suggesting that further accumulation of the drug did not occur. Furthermore, hourly monitoring on the last day of drug administration did not reveal any difference, relative to the first dose, in peak levels, time to peak level appearance, or rate of disappearance of dopamine binding activity. This suggests that active metabolites do not accumulate nor is there induction of drug metabolism. Plasma levels of tiospirone were also obtained by high-performance liquid chromatography assay at similar time points. With repeated drug administration plasma tiospirone concentrations also achieved a steady state. Statistically significant increases in plasma half-life and area under the time-concentration curve were observed between day 1 and 28.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of buspirone in elderly subjects

Twenty-four men and 24 women ages 20-77 years received a single 15 mg oral dose of buspirone followed by 4 days of 15 mg tid administration. Plasma concentrations of buspirone and 1-pyrimidinylpiperazine following both single and multiple dosing were determined by RIA and GCMS, respectively. There were no significant differences between the young and elderly of either gender with regard to buspirone AUC, Cmax, Tmax and half-life values. The 1-PP AUC values were higher for young of either gender compared to the corresponding group of elderly subjects and the 1-PP Cmax values were higher for women than men. These differences are unlikely to be of clinical significance. The buspirone and 1-PP AUC values for a dosing interval during multiple dosing are not significantly different than the respective single dose AUC values. Buspirone treatment was well-tolerated by all subjects even though the 45 mg/day dose was 3 times the recommended starting dose in clinical practice. Overall, the lack of marked or consistent differences in buspirone or 1-PP pharmacokinetics in elderly subjects compared to younger subjects of the same gender suggest there is no need to alter the initial dose of buspirone based solely on patient age.

Lack of interaction between cimetidine and buspirone

Simultaneous administration of cimetidine and many benzodiazepine anxiolytics has resulted in decreased body clearance and marked prolongation of the half-life of these agents. The pharmacokinetic interaction of buspirone, a new nonbenzodiazepine anxiolytic, and cimetidine was studied in 10 healthy male volunteers. Each received, in order, buspirone 45 mg/day (days 1-7), no drug (days 8-14), cimetidine 1 g/day (days 15-21), buspirone 45 mg/day plus cimetidine 1 g/day (days 22-28), and cimetidine 1 g/day (days 29-31). Buspirone and 1-pyrimidinyl piperazine (1-PP), an active metabolite, pharmacokinetics, urinary excretion of cimetidine, a manual dexterity test, the Stroop color-word interference test, and a visual analog mood scale were evaluated on each treatment. There were no significant (p greater than 0.05) differences among treatments for any measurement except for a slight (31%) but significant (p less than 0.05) increase in the 1-PP Cmax value. These results suggest that within the normal therapeutic dosage ranges for both drugs, it is unlikely that a clinically significant interaction between them will occur.