The pharmacokinetics of
tirilazad and
U-89678 (an active metabolite) were evaluated in 55 adults (48 males, 7 females) with moderate or severe
head injury who received 10.0 mg/kg/day
tirilazad mesylate for 5 days. Trough plasma samples were obtained daily; serial plasma samples were obtained over one dosing interval on day 5. Plasma
tirilazad and
U-89678 were quantified by HPLC. Sixty-two percent of the subjects received concomitant
anticonvulsants, of which 91% received
phenytoin. Plasma
tirilazad and
U-89678 concentrations in head-injured patients were similar to or lower than those observed in healthy volunteers. Sufficient data were available to calculate pharmacokinetic parameters for day 5 in 26 patients; 11 received no
anticonvulsants. The AUC0-6 (are under the concentration-time curve at 0-6 h) for
tirilazad mesylate on day 5 in patients receiving
anticonvulsants (median = 4972 ng h/mL) differed significantly from that in patients not receiving
anticonvulsants (median = 9704 ng h/mL) (p = 0.0051). Similarly, the AUC0-6 of
U-89678 in patients receiving
anticonvulsants (median = 561 ng h/mL) was significantly different from that in patients who were not (median = 2494 ng h/mL) (p = 0.0016). Comparison of pharmacokinetic data from patients not receiving
anticonvulsants to historical data in healthy volunteers suggests that
head injury has little effect on
tirilazad pharmacokinetics within 5 days of injury. These results suggest that the major factor affecting
tirilazad pharmacokinetics in head-injured patients is concomitant use of
enzyme-inducing
anticonvulsants.