L. E. DAVIS, C. A. DAVIS AND J. D. BAGGOT 
727 
PHENYLBUTAZONE 25mg/kg 
2 - 
' 1 1 1 1 » 1 
2 <l 6 8 12 2". 
II-'E (hrs) 
Figure 11. — Disappearance of phenylbutazone from 
the plasma of several species following intravenous 
injection (25 mg/kg). 
fate was a minor product in all species but was 
quantitatively important in ponies and goats. 
Oxyphenbutazone 
Oxyphenbutazone was studied in the same 
manner as phenylbutazone. These data are 
shown in Figures 13-16. This drug was elimi- 
nated more rapidly in all species, except the cat, 
than was phenylbutazone. These data further 
substantiate the importance of biotransfor- 
mation in species differences in the pharmacoki- 
netics of drugs. Phenylbutazone was rapidly ox- 
idized to oxyphenbutazone in the cat and hence 
! had a short half-life. Oxyphenbutazone was 
quite persistent in the plasma of cats because of 
the relative deficiency of glucuronyl transfer- 
ase. 
I The extent of oxyphenbutazone-plasma pro- 
' tein binding in all species was appreciably 
lower than that observed in human plasma. 
This was not as important factor in the phar- 
macokinetics of oxyphenbutazone as it was in 
the case of phenylbutazone. 
Following oral administration, oxphenbuta- 
zone was absorbed to about the same extent and 
at the same rate as phenylbutazone in cats and 
ponies. It was better absorbed by swine and less 
well absorbed in goats and dogs than was phenyl- 
butazone. 
Pentobarbital 
Pentobarbital was studied in 16 ponies, 16 
swine, 8 dogs and 8 cats. The kinetic parame- 
ters were evaluated in all animals following I.V. 
administration of the drug at a dosage of 10 
mg/kg. Subsequently, each species group was 
divided into four treatment groups. The control 
group received no treatment, other groups re- 
ceived 1, 2.7 or 7.3 mg/kg of pentobarbital 
orally, each day, for six months. The kinetic 
parameters were evaluated in each individual 
(10 mg/kg, I.V.) at one-month intervals. In 
addition, studies were conducted in kids, pup- 
PHENYLBUTAZONE lOmg/kg ORAL 
TIME (hrs) 
Figure 12. — Concentrations of phenylbutazone in the 
plasma following oral administration (10 mg/kg). 
