Objective—To validate use of high-performance liquid
chromatography (HPLC) in determining
imipramine concentrations in equine serum and to
determine pharmacokinetics of imipramine in narcoleptic
Animals—5 horses with adult-onset narcolepsy.
Procedure—Blood samples were collected before
(time 0) and 3, 5, 10, 15, 20, 30, and 45 minutes and
1, 2, 3, 4, 6, 8, 12, and 24 hours after IV administration
of imipramine hydrochloride (2 or 4 mg/kg of body
weight). Serum was analyzed, using HPLC, to determine
imipramine concentration. The serum concentration-versus-time curve for each horse was analyzed
separately to estimate pharmacokinetic values.
Results—Adverse effects (muscle fasciculations,
tachycardia, hyperresponsiveness to sound, and
hemolysis) were detected in most horses when
serum imipramine concentrations were high, and
these effects were most severe in horses receiving 4
mg of imipramine/kg. Residual adverse effects were
not apparent. Value (mean ± SD) for area under the
curve was 3.9 ± 0.7 h × μg/ml, whereas volume of
distribution was 584 ± 161.7 ml/kg, total body clearance
was 522 ± 102 ml/kg/h, and mean residence
time was 1.8 ± 0.6 hours. One horse had signs of narcolepsy
6 and 12 hours after imipramine administration;
corrresponding serum imipramine concentrations
were less than the therapeutic range.
Conclusions and Clinical Relevance—Potentially
serious adverse effects may be seen in horses administered
doses of imipramine that exceed a dosage of
2 mg/kg. Total body clearance of imipramine in horses
is slower than that in humans; thus, the interval
between subsequent doses should be longer in horses.
(Am J Vet Res 2001;62:783–786)
OBJECTIVE To determine the plasma pharmacokinetics and safety of 1% diclofenac sodium cream applied topically to neonatal foals every 12 hours for 7 days.
ANIMALS Twelve 2- to 14-day old healthy Arabian and Arabian-pony cross neonatal foals.
PROCEDURES A 1.27-cm strip of cream containing 7.3 mg of diclofenac sodium (n = 6 foals) or an equivalent amount of placebo cream (6 foals) was applied topically to a 5-cm square of shaved skin over the anterolateral aspect of the left tarsometatarsal region every 12 hours for 7 days. Physical examination, CBC, serum biochemistry, urinalysis, gastric endoscopy, and ultrasonographic examination of the kidneys and right dorsal colon were performed before and after cream application. Venous blood samples were collected at predefined intervals following application of the diclofenac cream, and plasma diclofenac concentrations were determined by liquid chromatography–mass spectrometry.
RESULTS No foal developed any adverse effects attributed to diclofenac application, and no significant differences in values of evaluated variables were identified between treatment groups. Plasma diclofenac concentrations peaked rapidly following application of the diclofenac cream, reaching a maximum of < 1 ng/mL within 2 hours, and declined rapidly after application ceased.
CONCLUSIONS AND CLINICAL RELEVANCE Topical application of the 1% diclofenac sodium cream to foals as described appeared safe, and low plasma concentrations of diclofenac suggested minimal systemic absorption. Practitioners may consider use of this medication to treat focal areas of pain and inflammation in neonatal foals.
Objectives—To assess safety and determine effects
of IV administration of formaldehyde on hemostatic
variables in healthy horses.
Animals—7 healthy adult horses.
Procedure—Clinical signs and results of CBC, serum
biochemical analyses, and coagulation testing including
template bleeding time (TBT) and activated clotting
time (ACT) were compared in horses given a
dose of 0.37% formaldehyde or lactated Ringer’s
solution (LRS), IV, in a 2-way crossover design. In a
subsequent experiment, horses received an infusion
of 0.74% formaldehyde or LRS. In another experiment,
horses were treated with aspirin to impair
platelet responses prior to infusion of formaldehyde
Results—Significant differences were not detected in
any variable measured between horses when given
formaldehyde or any other treatment. Infusion of
higher doses of formaldehyde resulted in adverse
effects including muscle fasciculations, tachycardia,
tachypnea, serous ocular and nasal discharge, agitation,
Conclusions and Clinical Relevance—Intravenous
infusion of formaldehyde at doses that do not induce
adverse reactions did not have a detectable effect on
measured hemostatic variables in healthy horses.
(Am J Vet Res 2000;61:1191–1196)
Objectives—To establish maximum oxygen consumption
(O2max) in ponies of different body
weights, characterize the effects of training of short
duration on O2max, and compare these effects to
those of similarly trained Thoroughbreds.
Animals—5 small ponies, 4 mid-sized ponies, and 6
Procedure—All horses were trained for 4 weeks.
Horses were trained every other day for 10 minutes
on a 10% incline at a combination of speeds equated
with 40, 60, 80, and 100% of O2max. At the beginning
and end of the training program, each horse performed
a standard incremental exercise test in which
O2max was determined. Cardiac output (), stroke
volume (SV), and arteriovenous oxygen content difference
(C [a-v] O2) were measured in the 2 groups of
ponies but not in the Thoroughbreds.
Results—Prior to training, mean O2max for each
group was 82.6 ± 2.9, 97.4 ± 13.2, and 130.6 ± 10.4
ml/kg/min, respectively. Following training, mean
O2max increased to 92.3 ± 6.0, 107.8 ± 12.8, and
142.9 ± 10.7 ml/kg/min. Improvement in O2max was
significant in all 3 groups. For the 2 groups of ponies,
this improvement was mediated by an increase in ;
this variable was not measured in the Thoroughbreds.
Body weight decreased significantly in the
Thoroughbreds but not in the ponies.
Conclusions and Clinical Relevance—Ponies have a
lower O2max than Thoroughbreds, and larger ponies
have a greater O2max than smaller ponies. Although
mass-specific O2max changed similarly in all groups,
response to training may have differed between
Thoroughbreds and ponies, because there were different
effects on body weight. (Am J Vet Res 2000;
Objective—To compare the analgesic efficacy of administration of butorphanol tartrate, phenylbutazone, or both drugs in combination in colts undergoing routine castration.
Design—Randomized controlled clinical trial.
Animals—36 client-owned colts.
Procedures—Horses received treatment with butorphanol alone (0.05 mg/kg [0.023 mg/lb], IM, prior to surgery and then q 4 h for 24 hours), phenylbutazone alone (4.4 mg/kg [2.0 mg/lb], IV, prior to surgery and then 2.2 mg/kg [1.0 mg/lb], PO, q 12 h for 3 days), or butorphanol and phenylbutazone at the aforementioned dosages (12 horses/group). For single-drug–treated horses, appropriate placebos were administered to balance treatment protocols among groups. All horses were anesthetized, and lidocaine hydrochloride was injected into each testis. Physical and physiological variables, plasma cortisol concentration, body weight, and water consumption were assessed before and at intervals after surgery, and induction of and recovery from anesthesia were subjectively characterized. Observers assessed signs of pain by use of a visual analogue scale and a numerical rating scale.
Results—Significant changes in gastrointestinal sounds, fecal output, and plasma cortisol concentrations were evident in each treatment group over time, compared with preoperative values. At any time point, assessed variables and signs of pain did not differ significantly among groups, although the duration of recumbency after surgery was longest for the butorphanol-phenylbutazone–treated horses.
Conclusions and Clinical Relevance—With intratesticular injections of lidocaine, administration of butorphanol to anesthetized young horses undergoing routine castration had the same apparent analgesic effect as phenylbutazone treatment. Combined butorphanolphenylbutazone treatment was not apparently superior to either drug used alone.
Procedure—Sarcocystis neurona-naïve weanling horses
were randomly allocated to 2 groups. Group A
received pyrantel tartrate at the labeled dose, and
group B received a nonmedicated pellet. Both groups
were orally inoculated with 100 sporocysts/d for 28
days, 500 sporocysts/d for 28 days, and 1,000 sporocysts/
d for 56 days. Blood samples were collected
weekly, and CSF was collected monthly. Ten seronegative
adult horses were monitored as untreated, uninfected
control animals. All serum and CSF samples
were tested by use of western blot tests to detect antibodies
against S neurona. At the end of the study, the
number of seropositive and CSF-positive horses in
groups A and B were compared by use of the Fisher
exact test. Time to seroconversion on the basis of treatment
groups and sex of horses was compared in 2 univariable
Cox proportional hazards models.
Results—After 134 days of sporocyst inoculation, no
significant differences were found between groups A
and B for results of western blot tests of serum or
CSF. There were no significant differences in number
of days to seroconversion on the basis of treatment
groups or sex of horses. The control horses remained
Conclusions and Clinical Relevance—Daily administration
of pyrantel tartrate at the current labeled dose
does not prevent S neurona infection in horses. (Am
J Vet Res 2005;66:846–852)