Interspecies comparisons of plasma half-life of trimethoprim in relation to body mass.

The relationship between body mass and plasma half-life of trimethoprim was studied in 10 different species of animals and man using published data. Log half-life was positively and significantly correlated to log body mass based on individual measurements in herbivorous animals (n = 23, P < 0.01), in herbivorous animals+pigs (n = 29, P < 0.01), in ungulates (n = 27, P < 0.01), in ruminants (n = 16, P < 0.01) and in non-herbivorous mammals, except pigs (n = 6, P < 0.05). The correlation was described by the allometric equations: t 1/2 beta = 27 W0.26 in herbivorous animals and t 1/2 beta = 125 W0.32 in non-herbivorous animals except pigs.

Interspecies variations in plasma half-life of ampicillin, amoxycillin, sulphadimidine and sulphacetamide related to variations in body mass.

The relationships between the half-lives during the elimination phase (t1/2 minutes) of ampicillin, amoxycillin, sulphadimidine and sulphacetamide and body mass (W, kg) between species of mammals and birds were examined using data from the authors' experiments and collected from the literature. Linear regression of the log half-lives of ampicillin, amoxycillin and sulphadimidine following intravenous injection on the log body mass for a variety of species of mammals and birds revealed significant correlations (r = 0.7709, n = 8, r = 0.7712, n = 8, r = 0.7749, n = 10). The interspecies relationships were described by the allometric equations t1/2 = 31.3 W0.16, t1/2 = 32.7 W0.12 and t1/2 = 129.2 W0.28, respectively. These equations may be of value for estimating dose intervals in species for which no relevant pharmacokinetic data are available.

Interspecies differences in the pharmacokinetics of kanamycin and apramycin.

Comparative studies on some selected pharmacokinetic parameters for kanamycin in sheep, goats, rabbits, chickens and pigeons, and for apramycin in sheep, rabbits, chickens and pigeons were carried out after intravenous administration of the two drugs at a dose of 10 mg/kg. The results revealed that a two-compartment open model was most suitable for kanamycin, while for apramycin a one-compartment open model was usually optimal. The log distribution rate constant (alpha) of kanamycin was significantly correlated to the log of the body mass (r = 0.919, n = 5, p < 0.05). Interspecies differences in the apparent volume of distribution (Vda) of kanamycin were small. These differences were larger for apramycin, as were the variations in the area under the serum concentration-time curve (AUC) and in the total body clearance (ClB) of both kanamycin and apramycin, both having almost a threefold difference depending on the species but without any correlation to body mass. The values of the log half-life of kanamycin in the mammals in this study and also those from data in the literature revealed a significant correlation with log body mass between animal species according to the equation: t1/2 beta = 38.47W0.21 (r = 0.7648, n = 10, p < 0.05).