Optimum serum sampling time for therapeutic monitoring of once-daily gentamicin dosage regimen

Abstract

To investigate the serum drug levels at 1-hr, 2-hr, 6-hr, 8-hr and 24-hr after the beginning of intravenous infusion of once-daily gentamicin in fifty Thai patients who continued using gentamicin once-daily dosage regimen for at least 3 days along with the clinical responses, in order to determine the optimum serum sampling time and its relatively reference concentration for therapeutic monitoring. The associations between nephrotoxicity and serum drug levels at different time points and the associations between efficacy and serum drug levels at different time points were determined. The nephrotoxicity was indicated in 8% of the patiens. The 6-hr and 8-hr serum gentamicin levels were associated significantly with nephrotoxicity (P = 0.001, by unpaired t-test). The 6-hr serum gentamicin levels of less than 3.0 mg/L or the 8-hr serum gentamicin levels of less than 2.0 mg/L provided a significantly lesser chance of developing nephrotoxicity (P<0.05, by Fisher's exact test). Thirty-seven bacterial infected patients were included in the evaluation of efficacy, favourable efficacy was recorded in 73% of these patients. The 1-hr serum gentamicin level was associated significantly with favourable efficacy (P<0.05, by unpaired t-test). The 1-hr serum gentamicin levels of more than or equal to 11.0 mg/L provided a significantly greater chance of having a favourable efficacy (P<0.05, by Fisher's exact test). The results got here suggested that the optimum serum sampling time points for therapeutic monitoring of once-daily gentamicin dosage regimen were at 1 hour after starting intravenous infusion with relatively reference concentration of more than or equal to 11.0 mg/L to provide a greater chance of having favourable efficacy, and at 6 or 8 hours after starting the drug administration with relatively reference concentrations of less than 3.0 mg/L and 2.0 mg/L respectively to reduce the risk of nephrotoxicity.