Relation of disposition kinetics to pharmacological effect of intravenous administration of chlorzoxazone in rats.
The quantitative relationship between a drug disposition and the pharmacological effect was examined in rats using chlorzoxazone (CZX), a centrally acting muscle relaxant, as a model drug. After intravenous administration of CZX, the decay of the plasma concentration was rapid and it was found that CZX obeyed one compartment open model in the dose range of 5 to 25 mg/kg studied. The pharmacological response intensity was determined by means of the crossed extensor reflex. The duration of the muscle relaxant effect was proportional to the logarithm of the dose of CZX. The time course of the calculated plasma concentration was well related to the pharmacological response intensity via a Hill's equation and the simulated pharmacological response intensity which was obtained by means of the equation was coincident to the time course of the response data. These results indicated that the time course of pharmacological response intensity was able to be predicted using the time course of plasma concentrations. From the analysis of the quantitative relationship between the concentration and the effect under the present experimental conditions studied, it was found that the biophase compartment was identical to the central compartment as long as the first order processes were proceeding. These findings implied that the time course of pharmacological response would be quantitatively predictable from the disposition kinetics of CZX after the intravenous administration.
Kaneko
I
I
Faculty of Pharmaceutical Sciences, Kobe-Gakuin University, Japan.
Fukumori
Y
Y
Fukuda
T
T
Takeuchi
Y
Y
D000818:Animals; D002698:Chloralose / Q000008:administration & dosage; D002753:Chlorzoxazone / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007274:Injections, Intraperitoneal; D007275:Injections, Intravenous; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects; D013997:Time Factors
D002698:Chloralose; D002753:Chlorzoxazone