Anticonvulsant Pharmacodynamics and Disposition of Triazolam in Rats

Abstract

Triazolam (TZ) is a triazolobenzodiazepine used in the treatment of insomnia that possesses significant anticonvulsant properties. Despite the widespread use of this drug, detailed pharmacokinetic–pharmacodynamic information is lacking, especially with respect to inhibition of seizure activity. TZ disposition has been described previously by methods with limited specificity, and the concentration–anticonvulsant effect relationship has not been characterized. The current studies were undertaken to examine TZ disposition with a specific HPLC method, and to evaluate the relationship between anticonvulsant effect and concentration in Sprague-Dawley rats. TZ pharmacokinetics were characterized after bolus or infusion administration; in a separate experiment, TZ pharmacodynamics were assessed with pentylenetetrazol-induced seizures. The systemic disposition of TZ could be described with a two-compartment model; systemic clearance ranged from 2.45 to 5.30L/h/ kg, steady-state volume of distribution ranged from 2.10 to 4.02L/kg, and mean residence time ranged from 47 to 65min. The concentration–effect relationship was well described by a simple Emax model: Emax, expressed as the ratio of post-TZ to pre-TZ threshold convulsant doses of pentylenetetrazol, was 9.9±0.7, and the EC50 values were 10.0±4.6ng/mL and 34.8±9.0ng/g in serum and whole brain tissue, respectively. Under single-dose conditions, TZ is a very potent anticonvulsant in the rat pentylenetetrazol seizure model.