Chronopharmacokinetic study of gentamicin in dogs.

The purpose of this experiment was to determine whether the time of day of single intravenous doses of gentamicin affects the drug's pharmacokinetics in dogs maintained under a 12 h light (08:00 to 20:00 h), 12 h dark (20:00 to 08:00 h) cycle. Using a crossover design, 6 mixed-breed male dogs received a single dose of 2 mg/kg of gentamicin at 8:00 or 20:00 h. Serial blood samples were collected and pharmacokinetic parameters were calculated following each timed dose. The concentration of the antibiotic was lower following the 08:00 h compared to the 20:00 h administration. When gentamicin was administered at 20:00 h, the initial concentration, mean residence time, and area under the disposition curve were significantly higher (p < 0.05) and the apparent volume of distribution of the central compartment, apparent volume of distribution, apparent volume of distribution at steady-state, and total body clearance (1.73+/-0.55 at 20:00 h versus 3.31+/-0.67 L/min/kg at 08:00 h) were significantly lower than for the 08:00 h administration (p < 0.05). Our results show that the pharmacokinetics of gentamicin exhibits significant temporal variation when administered to dogs at different times of day.