Lack of pharmacokinetic interaction between cimetidine and tirilazad mesylate

A comparison of the effects of tirilazad on subarachnoid hemorrhage-induced blood-brain barrier permeability in male and female rats

Phase III subarachnoid hemorrhage clinical trials have shown a beneficial effect of tirilazad only in men. One explanation for the decreased efficacy in women is that women metabolize the drug up to 60% faster than men. However, it is also possible that other more subtle differences between the sexes alter the pharmacodynamic response of women to tirilazad. The purpose of the present study was to compare the efficacy of tirilazad in attenuating early post-subarachnoid hemorrhage-induced blood-brain barrier damage in the rat, a species in which single-dose metabolism of the drug is comparable between males and females. Male and female rats were treated with 0.1, 0.3, 1.0, or 3.0 mg/kg tirilazad (intravenous) 10 minutes before and 2 hours after subarachnoid hemorrhage. At 3 hours posthemorrhage, the extent of blood-brain barrier damage, as measured by Evan's blue extravasation, did not differ between male and female vehicle-treated rats. In addition, treatment with tirilazad produced a similar effect in both males and females at all doses tested. At 0.3 mg/kg, blood-brain barrier damage was reduced 43.4% in males and 48.0% in females (P</=.01 vs vehicle), at 1.0 mg/kg, 33.1% in males and 29.1% in females (P</=.05), and at 3.0 mg/kg, 28.0% in males and 23.8% in females (P=NS). The lowest dose, 0.1 mg/kg, failed to protect the blood-brain barrier in both genders. These results suggest that gender differences do not significantly effect the blood-brain barrier protective efficacy of tirilazad following subarachnoid hemorrhage in the rat.

Population pharmacokinetics of tirilazad: effects of weight, gender, concomitant phenytoin, and subarachnoid hemorrhage

PURPOSE

Data collected during Phase I and II in the development of tirilazad were pooled and analyzed using nonlinear mixed effects models to assess covariates which might affect tirilazad pharmacokinetics.

METHODS

Four single dose and five multiple dose studies in normal volunteers were combined with two multiple dose studies performed in patients with subarachnoid hemorrhage (SAH) to identify factors related to intersubject variability in clearance (CL) and central compartment volume (Vc). Data from 253 subjects, which consisted of 7,219 tirilazad concentrations, were analyzed. The effects of weight, gender, patient versus volunteer status, and phenytoin use were evaluated.

RESULTS

Relative to male volunteers not receiving concomitant phenytoin, significant effects on clearance included: a 46% increase in volunteers receiving phenytoin, and an 82% increase in clearance associated with SAH patients (all of whom received phenytoin). Significant effects on Vc were: a 26% increase for female volunteers not receiving phenytoin, a 12% decrease for volunteers receiving concomitant phenytoin, a 152% increase for male SAH patients, and a 270% increase for female SAH patients. Incorporating patient covariate effects substantially reduced the interindividual variability (from 27.9% to 24.7% for clearance and from 48.2% to 37.5% for Vc). Residual variability was estimated at 66% coefficient of variation (CV) in SAH patients and at 22-48% CV over the range of predicted concentrations in normal volunteers.

CONCLUSIONS

The most important factors affecting tirilazad pharmacokinetics are the administration of phenytoin (increased CL) and SAH (increased Vc and residual variability). The effect of gender on tirilazad pharmacokinetics was modest.

Protective effects of tirilazad mesylate and metabolite U-89678 against blood-brain barrier damage after subarachnoid hemorrhage and lipid peroxidative neuronal injury

The 21-aminosteroid lipid-peroxidation inhibitor, tirilazad mesylate (U-74006F), recently was shown in a large multinational Phase III clinical trial to decrease mortality and improve neurological recovery in patients 3 months after onset of aneurysmal subarachnoid hemorrhage (SAH). A major tirilazad metabolite in animals and man, U-89678 is formed when the 4-5 double bond in the A-ring is reduced and has been postulated to contribute significantly to tirilazad's neuroprotective effects. In the first experiment of the present study, the authors compared the effects of tirilazad and U-89678 on acute blood-brain barrier (BBB) damage in rats subjected to SAH via injection of 300 microliters of autologous nonheparinized blood under the dura of the left cortex. The rats were treated by intravenous administration of either 0.3 or 1.0 mg/kg of tirilazad or U-89678 10 minutes before and 2 hours after SAH, and BBB damage was quantified according to the extravasation of the protein-bound Evans' blue dye into the injured cortex 3 hours post-SAH. The results revealed that 0.3 and 1.0 mg/kg tirilazad significantly reduced SAH-induced BBB damage 35.2% (p < 0.05) and 60.6% (p < 0.0001), respectively, in comparison to treatment with vehicle. The 0.3- and 1.0-mg/kg doses of U-89678 also decreased injury by 39.1% (p < 0.05) and 21.3% (not significant), respectively. In the second experiment, the investigators assessed the relative abilities of tirilazad and U-89678 to protect cultured neurons from iron-induced lipid peroxidative injury. Fetal mouse spinal cord cells were pretreated with 3, 10, or 30 microM tirilazad or U-89678 for 1 hour and then exposed to 200 microM ferrous ammonium sulfate (FAS) for 40 minutes. Cell viability was measured in terms of the uptake of [3H]alpha-(methyl)-aminoisobutyric acid 45 minutes after the FAS treatment. Both compounds enhanced neuronal survival in a concentration-dependent fashion. Although the two were equally efficacious, U-89678 was slightly more potent than its parent. On the basis of these findings, the authors conclude that the tirilazad metabolite, U-89678, possesses vaso- and neuroprotective properties that are essentially equivalent to the parent 21-aminosteroid. Hence, U-89678 probably contributes to the protective effects of tirilazad in SAH and other insults to the central nervous system.