Circadian variation in serum amikacin levels.

Variable serum amikacin levels have been reported in the same patient even after a steady state presumably has been reached. Therefore, the authors investigated the optimal schedule for monitoring serum levels of the drug in 50 neutropenic patients receiving continuous infusion amikacin therapy for infections. We found that levels obtained in the early morning hours were significantly higher than those obtained for the same patient in the evening. As these differences parallel those previously demonstrated for renal function, they may be explained by the pattern of drug clearance by the kidneys. We recommend that blood specimens for the detection of rising serum amikacin levels in a therapeutic setting be obtained in the early morning and at the same time each day so that meaningful comparisons of peak concentrations can be made. However, late evening samples should also be tested whenever dosage modifications are considered so that continuous therapeutic serum concentrations can be ensured.