Cobalt 60 radiotherapy for treatment of squamous cell carcinoma of the nasal cavity and paranasal sinuses in three horses.

Three adult horses underwent aggressive treatment of squamous cell carcinoma of the nasal cavity and paranasal sinuses, using course-fractionated cobalt 60 radiotherapy. Squamous cell carcinoma of the nasal cavity and paranasal sinuses is not commonly diagnosed in horses. Historically, horses with this type of neoplasm have not been treated or have undergone some form of surgery. The prognosis for long-term survival or cure has been poor. Long-term results of cobalt 60 radiotherapy were good to excellent and exceeded those usually reported for horses treated surgically. On the basis of these results, use of radiotherapy for these neoplasms is recommended.

Plasma pharmacokinetics of ranitidine HCl in adult horses.

Plasma pharmacokinetics of ranitidine HCl were investigated after intravenous (i.v.) and oral (p.o.) administration of 2.2 mg/kg drug to six healthy adult horses. Concentrations of ranitidine were determined using normal-phase, high-performance liquid chromatography. Plasma concentrations of ranitidine HCl declined from a mean of 5175 ng/mL at 5 min to 37 ng/mL at 720 min after i.v. administration. A three-exponent equation, Cp = A1 x e-k1t + A2 x e-k2t + A3 x e-k3t, best described data for all horses. Mean values for model-independent values calculated from the last quantifiable time point were: apparent volume of distribution (Vdss) = 1.07 L/kg; area under the curve (AUC) = 231,000 ng.min/mL: area under the moment curve (AUMC) = 26,900,000 ng.min2/mL; mean residence time (MRT) = 113 min; and clearance (Cl) = 9.8 mL/min.kg. Following p.o. administration, a two-exponent equation, Cp = A1 x e-k1t + A2 x e-k2t, best described the data for five horses: data for the remaining horse were best described by a three-exponent equation. Mean values of pharmacokinetic values from the p.o. study include: AUC = 59,900 ng x min/mL; AUMC = 10,600,000 ng x min2/mL; mean absorption time (MAT) = 58.9 min: Tmax = 99.2 min; Cmax = 237 ng/mL: and F = 27%.

Plasma pharmacokinetics of ranitidine HCl in foals.

Plasma pharmacokinetics of ranitidine HCl were investigated after intravenous (i.v.) and oral (p.o.) administration of drug to six healthy foals. Twelve- to sixteen-week-old foals received 2.2 mg ranitidine/kg i.v. and 4.4 mg ranitidine/kg p.o. Concentrations of ranitidine were determined using normal phase high performance liquid chromatography. Plasma concentrations of ranitidine HCl declined from a mean of 3266 ng/mL at 5 min to 11 ng/mL at 720 min after administration. The profile of the plot of concentrations of ranitidine HCl vs. time was best described by a two-exponent equation for two foals; data for the remaining four foals were best described by a three-exponent equation. Mean values for model-independent values were: apparent volume of distribution (Vdss) = 1.46 L/kg; area under the curve (AUC) = 167,442 ng.min/mL; area under the moment curve (AUMC) = 18,068,221 ng.min2/mL; mean residence time (MRT) = 108.9 min; and clearance (Cl) = 13.3 mL/min.kg. Following p.o. administration, a two-exponent equation best described data for five foals; data for the remaining foal were best described by a three-exponent equation. Mean values of the pharmacokinetic values from the p.o. study include: AUC = 126,413 ng.min/mL; AUMC = 18,039,825 ng.min2/mL; mean absorption time (MAT) = 32.0 min; observed time to maximum plasma concentration (Tmax) = 57.2 min; maximum observed plasma concentration (Cmax) = 635.7 ng/mL; and bioavailability (F) = 38%.

Indwelling cecal catheters for fluid administration in ponies.

Two different fluid solutions were infused through percutaneous cecal catheters in 6 healthy ponies to determine the effects on body weight; CBC; packed cell volume (PCV); total plasma protein concentration; plasma fibrinogen concentration; abdominal fluid analysis; concentrations of blood urea nitrogen (BUN), serum creatinine, Ca, total CO2 (TCO2), Na, Cl, K, and P; and fractional clearance (FC) of Na, Cl, K, and P. During intracecal administration of solution 1, FCNa and FCCl were significantly increased, whereas FCK and BUN were significantly decreased. During administration of solution 2, FCNa and serum P were significantly increased, while PCV was significantly decreased. All ponies developed peritonitis during the study. Complications included catheter-related problems, diarrhea, laminitis, and hypocalcemia. We concluded that hydration and electrolyte balance could be maintained by administration of crystalloid solutions intracecally, but that complications were associated with the procedure.

Urinary indices of horses after intravenous administration of crystalloid solutions.

Saline or glucose solution was infused for approximately 4 hours into six healthy mares in two separate experiments to determine the effect of infusion of crystalloid solutions on fractional excretion (FE) of sodium (Na), chloride (Cl), potassium (K), and phosphorus (P), ratio of urinary creatinine to serum creatinine (UCr/SCr), and ratio of urinary osmolality to serum osmolality (Uosm/Sosm). After intravenous infusion of either saline or glucose solution, FENa, FECl and FEP were significantly increased, whereas UCr/SCr and Uosm/Sosm were significantly decreased. In addition, FEK was significantly increased after infusion of glucose solution. It was concluded that urinary indices were altered by intravenous infusion of crystalloid solutions in healthy mares and that fluid therapy may interfere with the use of these indices for diagnostic purposes.

Idiopathic cecal rupture in foals after anesthesia for gastric endoscopy.

Cecal rupture has been reported as a complication of tape-worm infestation or parturition in horses. Often it occurs with no apparent predisposing factors. Spontaneous rupture on the medial surface of the cecum occurred in 2 of 19 foals, 12 to 24 hours after gastric endoscopy. The sites of rupture were identical in both foals. Rupture occurred despite prior deworming, withholding of food and water before anesthesia, and care in induction of anesthesia and recovery. Surgeons should be aware of the potential of cecal rupture in horses anesthetized for elective surgery.

Epidemiology of equine protozoal myeloencephalitis in North America based on histologically confirmed cases. A report.

Following a workshop on equine protozoal myeloencephalitis (EPM) convened at the Veterinary Medical Forum of the American College of Veterinary Internal Medicine in 1988, this survey of EPM in North America was developed. It is based upon 364 histologically confirmed case records from California, Florida, Illinois, Kentucky, New York, Ohio, Oklahoma, Ontario, Pennsylvania, and Texas up to 1988. The highest rate of infection was found in young Thoroughbred, Standardbred, and quarter horses. Differences in geographic location, sex, and month (season) of infection were not discernible. This report, the first comprehensive survey of EPM in North America, is intended to serve as a basis for evaluating future changes in prevalence and spread of EPM.

Pharmacokinetics and bioavailability of cephalothin in horse mares.

The pharmacokinetics and bioavailability of cephalothin given to 6 horse mares at a dosage level of 11 mg/kg of body weight IV or IM were investigated. The disposition of cephalothin given IV was characterized by a rapid disposition phase with a mean half-life of 2.89 minutes and a subsequent slower elimination phase with a mean half-life of only 14.7 minutes. The mean residence time of cephalothin was 10.6 +/- 2.11 minutes. The total plasma clearance of cephalothin averaged 13.6 ml/min/kg and was caused by metabolism and renal elimination. Renal clearance of cephalothin averaged 1.32 ml/min/kg and accounted for elimination of about 10.1% of the administered dose. The volume of distribution at steady state averaged 151 mg/kg. Plasma protein binding of cephalothin at a concentration of 10 micrograms/ml averaged 17.9 +/- 2.5%. Cephalothin was rapidly metabolized to desacetylcephalothin. Maximum plasma desacetylcephalothin concentrations were observed in the blood samples collected 5 minutes after IV doses and averaged 22.9 micrograms/ml. The apparent half-life of desacetylcephalothin in plasma was 41.6 minutes and its renal clearance averaged 4.49 +/- 2.43 ml/min/kg. An average of 33.9% of the dose was recovered in the urine as desacetylcephalothin. The maximum plasma cephalothin concentration after IM administration was 11.3 +/- 3.71 micrograms/ml. The terminal half-life was 47.0 minutes and was longer than the half-life after IV administration. The bioavailability of cephalothin given IM ranged from 38.3% to 93.1% and averaged 65.0 +/- 20.5%.

Pharmacokinetics and bioavailability of cefazolin in horses.

The pharmacokinetics and bioavailability of cefazolin given (IV, IM) to horses at the dosage of 11 mg/kg were investigated. The disposition of cefazolin given by IV route was characterized by a rapid disposition phase with a half-life of 5 to 10 minutes and a subsequent slower elimination phase with a half-life of 35 to 46 minutes. The total plasma clearance of cefazolin averaged 5.51 ml/min/kg and was due mainly to renal clearance (5.39 ml/min/kg) of unchanged drug. The volume of distribution at steady-state averaged 188 ml/kg. Plasma protein binding of cefazolin at a concentration of 10 micrograms/ml averaged 8.1 +/- 1.9%. Given by the IM route, cefazolin was rapidly absorbed; the extent of bioavailability was 78.4 +/- 18.8%, and the terminal half-life ranged from 49 to 99 minutes. Thus, cefazolin was extensively absorbed, but was eliminated more slowly than after IV administration.