Potassium Bromide

Small Animal/Exotics

20TH ANNIVERSARY

Compendium July 1999

PHARM PROFILE

POTASSIUM BROMIDE Julie M. Ducoté, DVM Texas A&M University

P

otassium bromide (KBr) is an anticonvulsant used to control seizures in dogs. KBr is not an approved drug; it is available for investigational use. Pet owners should be informed of this before the drug is prescribed.

PHARMACOLOGY Bromide competes with chloride for transport across the neuronal cell membrane, causing hyperpolarization of the cell membrane and thus raising the seizure threshold. KBr is absorbed orally and is eliminated by the kidneys. The half-life in dogs and cats is approximately 24 and 10 days, respectively.1,2 INDICATIONS Potassium bromide is indicated for use in combination with phenobarbital in dogs in which seizures are not well controlled with phenobarbital alone.1,3–5 KBr may also be used as the sole anticonvulsant drug in dogs in which phenobarbital is contraindicated because of its potential hepatotoxic effects.3–7 KBr is currently being evaluated for use in cats. CAUTIONS Common adverse effects seen with

KBr administration include ataxia, transient sedation, polyuria/polydipsia, and polyphagia.1 Dividing the daily dose and administering it with food may help to avoid gastrointestinal side effects. KBr should be used with caution in dogs with renal insufficiency. 8–10 Safety during pregnancy and lactation has not been established.

ACUTE TOXICITY Bromide toxicity is uncommon, although it may occur in dogs with renal insufficiency or those on a high dose of KBr. Signs of bromide toxicity include ataxia, sedation or stupor, and muscle spasm.8–10 Reducing the dose by 10% to 25% is usually adequate to resolve clinical signs.3 If the dog is stuporous because of acute overdose, gastric lavage should be performed; however, this will remove bromide only from the stomach. Diuresis with 0.9% sodium chloride will help lower serum bromide levels.8–9 DRUG INTERACTIONS Diuretics increase bromide excretion and lower serum bromide levels.10 Diets high in salt or chloride will increase bromide elimination and result in poor seizure control.11

Bromide and chloride compete for renal tubular reabsorption; increased dietary chloride will cause increased urinary excretion of bromide.11

DOSAGE AND ADMINISTRATION The recommended daily maintenance dose of KBr is 30 to 40 mg/kg orally 1,3–7; the pharmacokinetics of rectal and parenteral administration in dogs are currently under investigation.12 A loading dose of 450 to 600 mg/kg, usually divided over 5 days, can be used initially if rapid seizure control is desired.3,4,7,10 During these 5 days, it is also important to give the maintenance dose; thus, a typical loading protocol would be 120 mg/kg/day plus 35 mg/kg/day for 5 days. Serum bromide levels are measured within the first few days after completion of the loading dose. Side effects may be more likely during these 5 days. Weaning from phenobarbital (if required) should be done after 2 to 3 months of KBr maintenance therapy or after 1 to 2 days of the KBr loading dose. Therapeutic drug monitoring is essential and should be performed after the first 2 to 3 months of therapy, loading, or any change in dosage.4 Even when the patient is doing well,

Pharm Profile introduces drugs that are new to the veterinary market as well as new indications for existing drugs. If you would like Pharm Profile to cover a particular agent, please contact column editor GiGi Davidson, BS, RPh, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606; phone 919-821-9500 • fax 919-829-4225 • email [email protected].

Compendium July 1999

20TH ANNIVERSARY

Client Counseling Information ■ Although its use in animals is extralabel, KBr is a safe and effective anticonvulsant for dogs. It is frequently used alone or in combination with phenobarbital to control seizures. ■ Side effects of KBr are unusual but may include drowsiness, difficulty walking, or vomiting. Giving the drug with food may decrease stomach irritation. ■ KBr is administered orally in powder, capsule, or liquid solution; if given as a liquid, it should be kept refrigerated. ■ Dogs on KBr must be periodically returned to the veterinary hospital to have blood drawn to ensure that serum bromide levels are within the therapeutic range (i.e., the range at which most dogs’ seizures are controlled).

serum bromide levels should be checked every 6 months. Therapeutic serum levels for most dogs are 1 to 3 mg/ml but may vary depending on the animal’s tolerance.3,4,10 Many diagnostic and clinical pharmacology laboratories can measure bromide levels (the cost is usually $15 to $30).

PREPARATIONS Potassium bromide is available in powder form from any chemical supply company (request medicinal or American Chemical Society [ACS] grade).4 Many pharmacists frequently compound KBr into liquid solutions, capsules, and chewable tablet forms. STORAGE AND HANDLING Potassium bromide in powder or capsule form should be stored at room temperature. Once formulated into a liquid solution, it should be kept refrigerated and discarded after 6 months.4

Small Animal/Exotics

References 1. Podell M, Fenner WR: Bromide therapy in refractory canine idiopathic epilepsy. J Vet Intern Med 7:318–327, 1993. 2. George K, Boothe DM, Nguyen J, LeGrange S: Disposition of bromide in cats following oral administration of the potassium salt (Abstr). Proc 14th ACVIM Forum:757, 1996. 3. Trepanier LA: Use of bromide as an anticonvulsant for dogs with epilepsy. JAVMA 207(2):163–166, 1995. 4. Boothe DM: Anticonvulsant therapy in small animals. Vet Clin North Am Small Anim Pract 28(2):411–448, 1998. 5. Pearce LK: Potassium bromide as an adjunct to phenobarbital for the management of uncontrolled seizures in dogs. Prog Vet Neurol 1(1):95–101, 1990. 6. Podell M: How to keep epileptic dogs out of your emergency clinic. Proc 15th ACVIM Forum:292–293, 1997. 7. Sisson A: Current experiences with anticonvulsants in dogs and cats. Proc 15th ACVIM Forum:596–598, 1997. 8. Nichols ES, Trepanier LA, Linn K: Bromide toxicosis secondary to renal insufficiency in an epileptic dog. JAVMA 208(2):231–233, 1996. 9. Yohn SE, Morrison WB, Sharp PB: Bromide toxicosis (bromism) in a dog treated with potassium bromide for refractory seizures. JAVMA 201(3):468–470, 1992. 10. Plumb DC: Veterinary Drug Handbook. Ames, IA, Iowa State University Press, 1995, pp 89–90. 11. Shaw N, Trepanier LA, Center SA, Garland S: High dietary chloride content associated with loss of therapeutic serum bromide concentrations in an epileptic dog. JAVMA 208(2):234–236, 1996. 12. Dewey CW, Ducoté JM, Coates JR, et al: Intrarectally administered potassium bromide loading in normal dogs. J Vet Intern Med 13:238, 1999.

ABOUT THE AUTHOR Dr. Ducoté is affiliated with the Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, Texas.