The effect of oral phenylbutazone on whole blood platelet aggregation in the dog.

Platelet aggregation to collagen, arachidonic acid and adenosine diphosphate was evaluated in six dogs using a whole blood electronic aggregometer. The six dogs were then given phenylbutazone orally according to four different dosage levels and durations of treatment. Aggregation responses were measured at established intervals of time following phenylbutazone administration. Data on untreated dogs indicated that arachidonic acid, at a final concentration of 50 micrograms/mL and collagen, at a final concentration of 5 micrograms/mL, were useful agents for studying whole blood platelet aggregation in the dog, but adenosine diphosphate, at a final concentration of 30 microM was not. The high single dose (900 mg) of phenylbutazone significantly inhibited platelet aggregation to arachidonic acid at 1.5,4,7 and 12 hours following administration. The results indicated that the whole blood electronic aggregometer was of limited value in detecting subtle changes in platelet aggregation. It was concluded, however, that the instrument is potentially useful as a rapid screening aid for detecting canine patients at high risk of platelet-related bleeding problems.