title: Circadian variations in the pharmacokinetics, tissue distribution and urinary excretion of nifedipine after a single oral administration to rats.
abstract: Circadian variations in the pharmacokinetics, tissue distribution and urinary excretion of nifedipine were examined in fasted rats after administering a single oral dose at three different dosing times (08:00 am, 16:00 pm, 00:00 am). The plasma concentrations, the areas under the plasma concentration-time curve from zero to 6 h (AUC(0-6 h)) and the peak plasma concentration (C(max)) were significantly higher in the rats dosed at 08:00 am (immediately inactive), and was lower at 16:00 pm (most inactive) and 00:00 am (most active). The time to reach the C(max) (T(max)) was the shortest in the rats dosed at 08:00 am. It was very interesting to observe the double peak phenomena in the plasma concentration profiles, showing a larger peak followed by a smaller peak. There was a dosing time dependency on the tissue distribution 30 min after administration, showing a similar tendency to the pharmacokinetic behavior. However, there was no distinct dosing time dependency observed at 2 h after administration due to the extensive disposition. The cumulative urine excretion of nifedipine in the rats dosed at 08:00 am was significantly higher (about two-fold) than in those dosed at 16:00 pm and 00:00 am. The pharmacokinetics of nifedipine in the rats was consistent with that observed in human subjects in terms of the day-night clock time but the biological time was the opposite, as marked by the rest-activity cycles. These results may help to explain the circadian time-dependency of nifedipine pharmacokinetics.
authors.affiliation: National Research Laboratory for Bioavailability Control, College of Pharmacy, Kangwon National University, Chuncheon 200-701, Korea.
authors.forename: Qing-Ri
authors.initials: QR
authors.lastname: Cao
authors.forename: Tae-Wan
authors.initials: TW
authors.lastname: Kim
authors.forename: Jun Shik
authors.initials: JS
authors.lastname: Choi
authors.forename: Beom-Jin
authors.initials: BJ
authors.lastname: Lee
mesh_terms: D000284:Administration, Oral; D000818:Animals; D002121:Calcium Channel Blockers / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D002940:Circadian Rhythm / Q000502:physiology*; D008297:Male; D008657:Metabolic Clearance Rate; D009543:Nifedipine / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
chemical_list: D002121:Calcium Channel Blockers; D009543:Nifedipine