Variation in plasma halflife of gentamicin between species in relation to bodyweight and taxonomy

Data on the plasma halflife of gentamicin during the elimination phase were collected from the literature for 30 species for analysis of the effects of bodyweight and taxonomy. Log halflife was significantly correlated to log bodyweight between species of birds (r = 0.784, n = 9, P less than 0.05) and mammals (r = 0.873, n = 13, P less than 0.001), but not among the poikilotherms (n = 9). The slopes of regressions of log halflife on log bodyweight for mammal and bird species did not differ significantly (0.27 +/- 0.045 and 0.32 +/- 0.095, respectively) but the elevations did (t = 2.73, P less than 0.05). The variations in halflife between species in relation to bodyweight and taxonomy were broadly consistent with variations in glomerular filtration rate. The results illustrate the value of interspecies comparisons of pharmacokinetic data for estimating appropriate dosage regimes for vertebrates for which no specific data are available.