Objective—To compare serum disposition of sulfamethoxazole
and trimethoprim after IV administration
to donkeys, mules, and horses.
Animals—5 donkeys, 5 mules, and 3 horses.
Procedure—Blood samples were collected before
(time 0) and 5, 15, 30, and 45 minutes and 1, 1.25, 1.5,
1.75, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 8, 10, and 24 hours
after IV administration of sulfamethoxazole
(12.5 mg/kg) and trimethoprim (2.5 mg/kg). Serum
was analyzed in triplicate with high-performance liquid
chromatography for determination of sulfamethoxazole
and trimethoprim concentrations.
Serum concentration-time curve for each animal was
analyzed separately to estimate noncompartmental
Results—Clearance of trimethoprim and sulfamethoxazole
in donkeys was significantly faster
than in mules or horses. In donkeys, mean residence
time (MRT) of sulfamethoxazole (2.5 hours) was less
than half the MRT in mules (6.2 hours); MRT of
trimethoprim in donkeys (0.8 hours) was half that in
horses (1.5 hours). Volume of distribution at steady
state (Vdss) for sulfamethoxazole did not differ, but
Vdss of trimethoprim was significantly greater in horses
than mules or donkeys. Area under the curve for
sulfamethoxazole and trimethoprim was higher in
mules than in horses or donkeys.
Conclusions and Clinical Relevance—Dosing intervals
for IV administration of trimethoprim-sulfamethoxazole
in horses may not be appropriate for
use in donkeys or mules. Donkeys eliminate the
drugs rapidly, compared with horses. Ratios of
trimethoprim and sulfamethoxazole optimum for
antibacterial activity are maintained for only a short
duration in horses, donkeys, and mules. (Am J Vet Res
Objective—To describe the pharmacokinetics of
phenylbutazone and oxyphenbutazone after IV administration
in miniature donkeys.
Animals—6 clinically normal miniature donkeys.
Procedure—Blood samples were collected before
and 5, 10, 20, 30, 45, 60, 90, 120, 180, 240, 300, 360,
and 480 minutes after IV administration of phenylbutazone
(4.4 mg/kg of body weight). Serum was analyzed
in triplicate by use of high-performance liquid
chromatography for determination of phenylbutazone
and oxyphenbutazone concentrations. The serum
concentration-time curve for each donkey was analyzed
separately to estimate model-independent pharmacokinetic
Results—Serum concentrations decreased rapidly
after IV administration of phenylbutazone, and they
reached undetectable concentrations within 4 hours.
Values for mean residence time ranged from 0.5 to
3.0 hours (median, 1.1 hour), whereas total body
clearance ranged from 4.2 to 7.5 ml/kg/ min (mean,
5.8 ml/kg/ min). Oxyphenbutazone appeared rapidly in
the serum; time to peak concentration ranged from
13 to 41 minutes (mean, 26.4 minutes), and peak concentration
in serum ranged from 2.8 to 4.0 mg/ml
(mean, 3.5 μg/ml).
Conclusion and Clinical Relevance—Clearance of
phenylbutazone in miniature donkeys after injection of
a single dose (4.4 mg/kg, IV) is rapid. Compared with
horses, miniature donkeys may require more frequent
administration of phenylbutazone to achieve therapeutic
efficacy. (Am J Vet Res 2001;62:673–675)
Objective—To compare plasma disposition of the
R(–) and S(+) enantiomers of carprofen after IV administration
of a bolus dose to donkeys and horses.
Animals—5 clinically normal donkeys and 3 clinically
Procedure—Blood samples were collected from all
animals at time 0 (before) and at 10, 15, 20, 30, and
45 minutes and 1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 24,
28, 32, and 48 hours after IV administration of a
bolus of carprofen (0.7 mg/kg). Plasma was analyzed
in triplicate via high-performance liquid chromatography
to determine the concentrations of the
carprofen enantiomers. A plasma concentration-time
curve for each donkey and horse was analyzed
separately to estimate noncompartmental pharmacokinetic
Results—In donkeys and horses, the area under the
plasma concentration versus time curve (AUC) was
greater for the R(–) carprofen enantiomer than it was
for the S(+) carprofen enantiomer. For the R(–) carprofen
enantiomer, the AUC and mean residence time
(MRT) were significantly less and total body clearance
(ClT) was significantly greater in horses, compared
with donkeys. For the S(+) carprofen enantiomer,
AUC and MRT were significantly less and ClT and
apparent volume of distribution at steady state were
significantly greater in horses, compared with donkeys.
Conclusions and Clinical Relevance—Results have
suggested that the dosing intervals for carprofen that
are used in horses may not be appropriate for use in
donkeys. (Am J Vet Res 2004;65:1479–1482)
Objective—To determine the disposition of a bolus of meloxicam (administered IV) in horses and donkeys (Equus asinus) and compare the relative pharmacokinetic variables between the species.
Animals—5 clinically normal horses and 5 clinically normal donkeys.
Procedures—Blood samples were collected before and after IV administration of a bolus of meloxicam (0.6 mg/kg). Serum meloxicam concentrations were determined in triplicate via high-performance liquid chromatography. The serum concentration-time curve for each horse and donkey was analyzed separately to estimate standard noncompartmental pharmacokinetic variables.
Results—In horses and donkeys, mean ± SD area under the curve was 18.8 ± 7.31 μg/mL/h and 4.6 ± 2.55 μg/mL/h, respectively; mean residence time (MRT) was 9.6 ± 9.24 hours and 0.6 ± 0.36 hours, respectively. Total body clearance (CLT) was 34.7 ± 9.21 mL/kg/h in horses and 187.9 ± 147.26 mL/kg/h in donkeys. Volume of distribution at steady state (VDSS) was 270 ± 160.5 mL/kg in horses and 93.2 ± 33.74 mL/kg in donkeys. All values, except VDSS, were significantly different between donkeys and horses.
Conclusions and Clinical Relevance—The small VDSS of meloxicam in horses and donkeys (attributed to high protein binding) was similar to values determined for other nonsteroidal anti-inflammatory drugs. Compared with other species, horses had a much shorter MRT and greater CLT for meloxicam, indicating a rapid elimination of the drug from plasma; the even shorter MRT and greater CLT of meloxicam in donkeys, compared with horses, may make the use of the drug in this species impractical.