To investigate the effect of high doses of orally administered levothyroxine sodium (LT4) on serum concentrations of triiodothyronine (T3) and thyroxine (T4) in euthyroid horses.
12 healthy adult horses.
10 horses initially received water (vehicle) or 240 mg (5X treatment) or 480 mg (10× treatment) of LT4, and blood samples were collected at baseline (0 hours) and 0.5, 1, 2, 4, 6, 8, 10, 12, 18, 24, 48, 72, 96, and 120 hours after treatment to measure serum T3 and T4 concentrations. Three horses then received 480 mg of LT4 for 14 days, and T4 concentration was measured on days 0, 14, 21, 28, and 35. Changes in T3 and T4 concentrations were compared over time and among treatments.
One-time administration of LT4 resulted in variable but significant increases in both T3 and T4 concentrations for up to 120 hours; however, T3 and T4 concentrations rarely exceeded reference intervals with either treatment. Prolonged administration of 480 mg of LT4 resulted in a 15-fold increase in T4 concentration after 14 days, but concentration returned to day 0 values within 21 days after LT4 administration was discontinued.
CONCLUSIONS AND CLINICAL RELEVANCE
In euthyroid horses, administration of a high dose of LT4 resulted in mild increases in thyroid hormone concentrations; however, prolonged administration of high doses of LT4 resulted in markedly increased thyroid hormone concentrations that returned to pretreatment values within 3 weeks after discontinuation of LT4 administration. These results indicated complex kinetics of LT4 and suggested a possible saturation of T4 excretion in euthyroid horses.
ANIMALS 20 healthy pet cats with a history of fractious behavior or signs of stress during veterinary examination.
PROCEDURES Cats were scheduled for 2 veterinary visits 1 week apart and randomly assigned to receive a capsule containing 100 mg of gabapentin (13.0 to 29.4 mg/kg [5.9 to 13.4 mg/lb]) or placebo (lactose powder) prior to the first visit and the opposite treatment prior to the second visit. Owners were instructed to administer the assigned capsule orally 90 minutes prior to placing the cat into a carrier and transporting it to the veterinary hospital. Standardized physical examinations and blood pressure readings were performed. Owners assigned a cat stress score during transportation and examination, and the veterinarian assigned a compliance score at the visit. Scores were compared between treatments, controlling for various factors.
RESULTS Owner-assessed cat stress scores during transportation and veterinary examination and veterinarian-assessed compliance scores were significantly lower when cats received gabapentin than when they received the placebo. Sedation was a common effect of gabapentin administration, and ataxia, hypersalivation, and vomiting were also reported. All effects resolved within 8 hours after gabapentin administration.
CONCLUSIONS AND CLINICAL RELEVANCE Owners' perception of stress in their cats is a primary reason for failing to seek veterinary care. Results of this study suggested that gabapentin is a safe and effective treatment for cats to help reduce stress and aggression and increase compliance for transportation and veterinary examination.