OPTIMIZATION OF BLOOD SAMPLING TIME AFTER INTRAVENOUS BOLUS DOSES OF GENTAMICIN

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Abstract
Comparisons were made, based on a one-compartment model, between predicted serum concentrations obtained at various sampling times after i.v. bolus and i.m. injections of gentamicin. Post-dose concentrations 1 h after i.m. injection were within 3% of the maximum concentration at steady-state, indicating that this was the optimal sampling time. Serum concentrations 1 h post-i.v. bolus were less than 7% different from those 1 h post-i.m. injection. In a clinical trial, blood samples taken earlier during the distribution phase of the drug, after an i.v. bolus, resulted in serum concentrations which were up to 74% higher than concentrations at 1 h. A survey of a sample of U.K. hospitals showed that only 41% were taking samples at 1 h post i.v. bolus of gentamicin. The majority of hospitals recommended a range of post-dose serum concentrations between 4 and 12 mg/1 for patients with septicaemia, but when adjusted for errors related to sampling time, 36% of hospitals recommended a minimum which was equivalent to less than 4 mg/1 at h post dose. Post-dose concentrations of gentamicin should be measured in samples taken 1 h after either i.v. bolus and i.m. injections.