Sampling time for serum gentamicin levels

A survey in 53 UK hospitals showed that 44% of clinical microbiologists recommended post-dose serum gentamicin concentrations to be measured at less than 40 min after an iv bolus dose. Serum gentamicin concentrations were measured in ten patients following bolus iv and im injections. Distribution of the drug occurred for up to 45 min following iv doses and maximum serum concentrations occurred at 45 to 60 min after im injection. The data validate current guidelines to sample at 60 min post bolus iv and im doses. Earlier sampling after iv bolus injections may result in significantly higher gentamicin concentrations, leading to potential interpretive errors of clinical significance.