Objective—To determine the disposition of orally
administered cefpodoxime proxetil in foals and adult
horses and measure the minimum inhibitory concentrations
(MICs) of the drug against common bacterial
pathogens of horses.
Animals—6 healthy adult horses and 6 healthy foals
at 7 to 14 days of age and again at 3 to 4 months of
Procedure—A single dose of cefpodoxime proxetil
oral suspension was administered (10 mg/kg) to each
horse by use of a nasogastric tube. In 7- to 14-day-old
foals, 5 additional doses were administered intragastrically
at 12-hour intervals. The MIC of cefpodoxime
for each of 173 bacterial isolates was determined by
use of a commercially available test.
Results—In 7- to 14-day-old foals, mean ± SD time to
peak serum concentration (Tmax) was 1.7 ± 0.7 hours,
maximum serum concentration (Cmax) was 0.81 ±
0.22 µg/mL, and elimination half-life (harmonic mean)
was 7.2 hours. Disposition of cefpodoxime in 3- to 4-month-old foals was not significantly different from
that of neonates. Adult horses had significantly higher
Cmax and significantly lower Tmax, compared with
values for foals. The MIC of cefpodoxime required to
inhibit growth of 90% of isolates for Salmonella enterica,
Escherichia coli, Pasteurella spp, Klebsiella spp,
and β-hemolytic streptococci was 0.38, 1.00, 0.16,
0.19, and 0.09 µg/mL, respectively.
Conclusions and Clinical Relevance—Oral administration
at a dosage of 10 mg/kg every 6 to 12 hours
would appear appropriate for the treatment of equine
neonates with bacterial infections. (Am J Vet Res 2005;66:30–35)
Objective—To determine the pharmacokinetics of
azithromycin and its concentration in body fluids and
bronchoalveolar lavage cells in foals.
Animals—6 healthy 6- to 10-week-old foals.
Procedure—Azithromycin (10 mg/kg of body weight)
was administered to each foal via IV and intragastric
(IG) routes in a crossover design. After the first IG
dose, 4 additional IG doses were administered at 24-hour intervals. A microbiologic assay was used to
measure azithromycin concentrations in serum, peritoneal
fluid, synovial fluid, pulmonary epithelial lining
fluid (PELF), and bronchoalveolar (BAL) cells.
Results—Azithromycin elimination half-life was 20.3
hours, body clearance was 10.4 ml/min·kg, and apparent
volume of distribution at steady state was 18.6
L/kg. After IG administration, time to peak serum concentration
was 1.8 hours and bioavailability was 56%.
After repeated IG administration, peak serum concentration
was 0.63 ± 0.10 µg/ml. Peritoneal and synovial
fluid concentrations were similar to serum concentrations.
Bronchoalveolar cell and PELF concentrations
were 15- to 170-fold and 1- to 16-fold higher than concurrent
serum concentrations, respectively. No
adverse reactions were detected after repeated IG
Conclusions and Clinical Relevance—On the basis
of pharmacokinetic values, minimum inhibitory concentrations
of Rhodococcus equi isolates, and drug
concentrations in PELF and bronchoalveolar cells, a
single daily oral dose of 10 mg/kg may be appropriate
for treatment of R equi infections in foals. Persistence
of high azithromycin concentrations in PELF and bronchoalveolar
cells 48 hours after discontinuation of
administration suggests that after 5 daily doses, oral
administration at 48-hour intervals may be adequate.
(Am J Vet Res 2001;62:1870–1875)
Procedure—Dogs were randomly assigned to 2
groups of 3 dogs in a crossover design. Diazepam
(0.5 mg/kg of body weight) was administered intravenously
to dogs in group 1 and intranasally to dogs
in group 2. Blood was collected from the jugular vein
of each dog into tubes containing lithium heparin
before and 3, 6, 9, 12, 15, 20, 30, 60, 120, 240, and
480 minutes following diazepam administration. After
a 4-day washout period, dogs in group 1 received
diazepam intranasally, dogs in group 2 received
diazepam intravenously, and blood was again collected.
Plasma concentration of BDZ was determined by
use of a fluorescence polarization immunoassay.
Results—Mean (± SD) peak plasma concentration of
BDZ following IV administration (1316 ± 216 µg/L)
was greater than that following IN administration
(448 ± 41 µg/L). Time to peak concentration was ≤ 3
minutes following IV administration and 4.5 ± 1.5
minutes following IN administration. Mean bioavailability
of BDZ following IN administration was
80 ± 9%.
Conclusions and Clinical Relevance—Diazepam is
rapidly and efficiently absorbed following IN administration
of the parenteral formulation. Plasma concentrations
match or exceed the suggested therapeutic
concentration (300 µg/L). Intranasal administration of
diazepam may be useful for treatment of seizures in
dogs by owners or when intravenous access is not
readily available. (Am J Vet Res 2000;61:651–654)