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Seasonal rhythmic changes in gentamicin pharmacokinetics was evaluated in 10 healthy male volunteers after single intravenous 80 mg administration of gentamicin at 9:00 a.m. during summer and winter. The mean terminal half-life and AUC of gentamicin were 3.56pm0.14;hr;and;25.03pm2.84;{mu}g/ml{cdot}hr in winter and 3.08pm0.41;hr;and;21.84pm2.51;{mu}g/ml{cdot}hr in summer. The mean total body clearance (CL_t) and elimination rate constant (k_{10}) of gentamicin was 3.17pm0.43;L/hr,;0.458pm0.06;hr^{-1};in;winter;and;3.66pm0.45;L/hr,;0.561pm0.07;hr^{-1} in summer, The mean volumn of distribution (V_{dss}) of gentamicin at steady state was 12.65pm1.09L in winter and 12.39pm1.25 L in summer. Serum concentrations of gentamicin in winter were increased significantly during 4-8 hr (p<0.05) compared to those of gentamicin in summer. The elimination rate constant (k_{10}) of gentamicin in winter was decreased significantly (p<0.05) compared to that of gentamicin in summer. The mean volume of distribution at steady state (V_{dss}), AUC, mean total body clearance (CL_t) and terminal half-life of gentamicin in the winter were increased but were not significant. The mean intrasubject fluctuations in terminal half-life, AUC and CL_t between winter and summer were 8.2, 11.0 and 6.0% respectively.
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