Warfarin in the dog: pharmacokinetics as related to clinical response

Warfarin was administered intravenously (i.v.) as a single dose of 1.5 mg/kg to healthy dogs and the pharmacokinetic parameters were investigated. Elimination could be described by a one-compartment open model. Values for the elimination half-life and apparent specific volume of distribution were 14.5 ± 4.1 h and 0.22 ± 0.04 litre/kg, respectively. Oral maintenance doses were calculated from the data collected following i.v. administration and administered every 12 h for a total of five doses after an initial i.v. loading dose of 1.5 mg/kg. Prothrombin times increased from a control value of 8.6 ± 0.3 sec to 55.2 ± 5.2 sec over a period of 96 h. Prothrombin time returned to control values by 62 h after withdrawal of the drug. We propose a dosage regimen of warfarin for anticoagulant therapy in the dog of 0.22 mg/kg to be given orally every 12 h. Prothrombin time should be monitored during therapy and the dose of warfarin modified according to the degree of suppression of coagulation factors desired.     

Pharmacokinetic studies of theophylline in dogs

The pharmacokinetics of theophylline were investigated in dogs following intravenous, single oral, and multiple oral doses of aminophylline. Mean half-life ( t _1/2) of theophylline following single intravenous administration was 5.7 h and the apparent specific volume of distribution ( V'd area) was 0.82 litre/kg. The bioavailability of theophylline was high (91%) following oral administration of aminophylline tablets and the absorption half-life ( t _{1/2 ab}) was 0.4 h.
Theophylline plasma concentrations observed following repeated oral administration of aminophylline tablets were somewhat greater than predicted. This suggests that theophylline plasma concentrations should be monitored and the dosage regimen individually adjusted in critically ill animals.     

BOOK REVIEW

ECG Interpretation in Dogs and Cats, Video produced by Provet for the Unit of Veterinary Continuing Education of the Royal Veterinary College     

Tissue distribution of tetraethylammonium (TEA) in dogs and goats

The tissue distribution of tetraethylammonium (TEA), a highly polar drug which does not undergo biotransformation, was studied in intact and nephrectomized dogs and goats. Values for β, the overall elimination rate constant, were significantly reduced by nephrectomy but species differences were not significant. Values for apparent specific volume of distribution (V'_d) were unexpectedly large and tissue to plasma ratios were 4.0 and 5.0 in the nephrectomized goat and dog, respectively. The distribution of TEA to various tissues followed closely the expected pattern of regional blood flow, although TEA attained concentrations in liver, heart, lungs and viscera in excess of the concentration in the plasma.     

Pharmacokinetics of lithium in the dog

The pharmacokinetics of lithium were determined in eight adult dogs. The data were fitted to a two-compartment model. Single intravenous doses of lithium chloride, and single oral doses of lithium carbonate were used. The mean plasma lithium half-life (t1/2) following the single intravenous dose was 21.6 h, and the mean apparent specific volume of distribution of the central compartment (V'c) was 0.189 l/kg. Mean bioavailability was 78.8% following oral administration.