title: Effect of the hour of administration on the pharmacokinetics of lidocaine in the rat.
abstract: The aim of the present study was to investigate an eventual influence of the hour of administration on lidocaine kinetics in the rat. 280 Wistar AF-SPF adult male rats were used for this study and maintained under controlled environmental conditions (LD: 06.00-18.00) during the month of October. A single 50 mg X kg-1 dose of lidocaine was given by intramuscular route, at four different fixed time points of a 24 hour period (i.e.: 10.00, 16.00, 22.00 and 04.00) to 70 rats. Blood samples were taken at the following time points: 5, 15, 30 min., 1, 2, 4 and 6 hours after the drug administration. Lidocaine plasma levels (free and bound) were determinated according to a specific gas chromatographic method. The data showed circadian variations of pharmacokinetic parameters:--Elimination half-life: max. 2.12 +/- 0.05 h at 10.00, min. 1.50 +/- 0.03 h at 16. --Initial concentration: max. 5.05 +/- 0.65 micrograms X ml-1 at 16.00; min. 2.97 +/- 0.29 micrograms X ml-1 at 04.00.--Elimination constant rate: max. 0.4618 +/- 0.0094 h-1 at 16.00, min 0.3279 +/- 0.0079 h-1 at 10.00.--Area under curve (experimental): max. 11.11 +/- 1.07 micrograms X kg-1 X h-1 at 16.00, min. 7.45 +/- 0.84 micrograms X kg-1 X h-1 at 04.00.--Apparent volume of distribution: max. 16.67 +/- 1,67 L X kg-1 at 04.00, min. 9.75 +/- 1.04 L X kg-1 at 16.00. The lidocaine-free fraction varied with time and the protein binding of lidocaine showed a circadian variation.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000042:Absorption; D000818:Animals; D001711:Biotransformation; D002940:Circadian Rhythm; D006207:Half-Life; D007273:Injections, Intramuscular; D007700:Kinetics; D008012:Lidocaine / Q000008:administration & dosage / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
chemical_list: D008012:Lidocaine