Bromide toxicosis (bromism) in a dog treated with potassium bromide for refractory seizures

A 4-year-old German Shepherd Dog was evaluated because of chronic hind limb lameness and recurrent seizures. Diagnostic evaluation of the dog confirmed rheumatoid arthritis and idiopathic epilepsy. The rheumatoid arthritis was treated with prednisone and piroxicam. The seizures were treated with phenobarbital plus clonazepam. The seizures were refractory and potassium bromide was substituted for clonazepam. The dog was reevaluated 4 months after initiation of potassium bromide treatment because of recurrence of arthritis signs. During hospitalization, the dog had neurologic signs, which progressed from depression to recumbency and stupor. Anisocoria, muscle pain, and hyporeflexia were noticed. Bromide toxicosis was diagnosed on the basis of toxic serum bromide concentration (2.7 mg/ml; therapeutic range, 1.0 to 2.0 mg/ml). Following cessation of potassium bromide treatment, the neurologic signs resolved. The seizures recurred 6 weeks after potassium bromide was discontinued. Bromide treatment was reinitiated at half the initial dosage. After 6 weeks, the serum bromide concentration was 1.9 mg/ml, and no seizures had been reported by the dog's owners. Therapeutic serum bromide concentrations in dogs has been reported to be 0.5 to 2.3 mg/ml. The serum bromide concentration at which toxic signs are expected is variable in human beings because individuals differ in their tolerance of the drug. Clinical trials are necessary to determine the toxic serum bromide concentrations in dogs. This case of bromism in a dog suggests that the dosage of potassium bromide should be based on serial measurement of serum bromide concentrations.