The effect of imepitoin, a recently developed antiepileptic drug, on thyroid parameters and fat metabolism in healthy Beagle dogs

• The effect of imepitoin administration on thyroid parameters and fat metabolism in dogs is evaluated.
• Imepitoin did not affect thyroid parameters over an 18-week period.
• Cholesterol increased significantly over time in the dogs on imepitoin.

Since early 2013, imepitoin has been used in most European countries for the management of recurrent single generalised epileptic seizures in dogs with idiopathic epilepsy. It has been reported that imepitoin is as effective as phenobarbital (PB) in controlling seizures in dogs with newly diagnosed idiopathic epilepsy and it has a clinically superior safety profile. As the use of imepitoin gains popularity, its effect on serum thyroid parameters warrants further investigation since long-term PB administration influences thyroid parameters in dogs, which could lead to misinterpretation of laboratory results and incorrect diagnosis of thyroidal illness. A prospective study was conducted to compare the effect of orally administered PB and imepitoin on serum concentrations of total thyroxine (TT4), triiodothyronine, free thyroxine, thyroglobulin autoantibodies, thyroid-stimulating hormone, cholesterol and triglycerides in healthy Beagle dogs. These parameters were determined prior to and at 6, 12 and 18 weeks after antiepileptic drug administration. The starting dose of PB (5 mg/kg PO twice daily; range, 4.4–6.0 mg/kg) was monitored and adjusted to obtain optimal therapeutic serum concentrations (30–35 g/mL). Imepitoin was administered at 30 mg/kg PO twice daily (range, 29.2–35.7 mg/kg).Imepitoin administration did not affect any of the thyroid parameters over an 18-week period. In contrast, serum TT4 concentrations decreased significantly over time in dogs receiving PB (P < 0.05). Serum cholesterol concentrations increased significantly over time in dogs in the imepitoin group, but not to the same extent as commonly seen in dogs with primary hypothyroidism.