Interspecies variation in the plasma halflife of oxytetracycline in relation to bodyweight

The relationship between halflife (t1/2, minutes) of oxytetracycline and bodyweight (W, kg) between species of mammals and birds was examined using data collected from the literature. Linear regression of the logarithm of the halflife of the elimination phase of oxytetracycline following intravenous injection on the logarithm of bodyweight for a variety of species of mammals and birds revealed a significant correlation between species (r = 0.602, n = 13, P less than 0.05). The interspecies relationship was described by the allometric equation; t1/2 = 160 W0.20. This suggests that there is about a 14-fold variation in t1/2 across the size range of terrestrial homoeotherms, and provides a guide to dosage regime for species in which oxytetracycline kinetics have not been studied.