Chronopharmacodynamics and chronopharmacokinetics of pethidine in mice

Many studies have demonstrated that the pharmacokinetics and pharmacodynamics of analgesic drugs vary according to the circadian time of drug administration. This study aims at determining whether the analgesic effect and pharmacokinetics of pethidine in male BALB/c mice are influenced by administration time.

A hot-plate test was used to evaluate the analgesic effect after pethidine (20 mg/kg) or saline injection at different dosing times. Mouse blood samples were collected at different intervals after dosing at 9:00 am and 9:00 pm, and were determined via liquid chromatography-tandem mass spectrometry (LC-MS/MS).

A significant 24-h rhythm was observed in the latency to thermal response at 30 min after dosing, with the peak during the dark phase and the nadir during the light phase. Tolerance to analgesic effect was produced after chronic pethidine injection at 9:00 am or 9:00 pm, and the recovery from tolerance was faster during the dark phase. The peak concentration (Cmax) and area under the concentration-time curve (AUC) of pethidine and its metabolite norpethidine were significantly higher during the dark phase than during the light phase, but the total serum clearance (CL/F) exhibited the opposite trend. The rhythm of drug plasma concentration was positively correlated with the analgesic effect.

These results suggest that the pharmacodynamics and pharmacokinetics of pethidine in mice vary significantly according to the dosing time, which implies that the time of administration should be considered in the rational clinical use of pethidine to maximise analgesia and minimise the adverse effects.