Pharmacokinetic and pharmacodynamic consequences of thiopental in renal dysfunction rats: evaluation with...

The purpose of this work was to investigate the disposition characteristics and pharmacodynamics of a barbiturate, thiopental, in renal dysfunction rats. Normal and renal dysfunction rats were infused with 40 and 20 mg/kg of thiopental, respectively. The quantitative electroencephalographic (EEG) method was used as the surrogate measure of pharmacological response. Signals from two electrodes fitted on the skull of rats were continuously measured, recorded and subjected to off-line analysis. Total amplitude (0.5-29.9Hz) from aperiodic analysis was taken as the EEG parameter. Thiopental concentration in plasma and cerebrospinal fluid (CSF) was assayed by an HPLC method. Steady-state volume of distribution was increased in renal dysfunction rats due to decreased plasma protein binding, while no change in clearance or volume of distribution based on the plasma unbound concentration was observed. Amplitude changes induced by thiopental in both normal and renal dysfunction rats were characterized by the sigmoidal Emax model. The unbound plasma concentration at half maximal effect was lowered by 30% in renal dysfunction rats as compared to the normal rats. In addition to considerable alteration in the pharmacokinetics of thiopental, it was also evident that renal impairment is associated with an increase in apparent pharmacological sensitivity, which is related to affinity.