Potassium bromide

A seizure occurs when nerve cells in the brain discharge abnormal electrical signals. The electrical charge within these cells is reduced by potassium bromide (KBr) to suppress seizure activity.

How much potassium bromide should a dog have?

There are a variety of forms of potassium bromide available, including liquid, capsule, and tablet. In general, potassium bromide is given once daily in the evening, or divided into two daily doses.

Normally, the starting dose is 30-40 milligrams (mg) per kilogram (kg) of body weight per day. An average Golden Retriever weighing 30 kg could receive between 900 and 1200 mg each day. It may be recommended that you start your dog on a higher dose to allow the blood concentrations to increase more rapidly. There is no one-size-fits-all method for dosing the drug in dogs.

Potassium bromide doses may be affected by other factors. Potassium bromide will be absorbed more quickly if a dog eats a high salt diet, and the reverse is also true. Changing a dog’s diet could increase or decrease potassium bromide levels.

Whenever the diet is altered (especially if the dog becomes sedated or has unexpected seizures), the blood concentrations of potassium bromide should be rechecked. Unless they are home cooked or prescribed for heart disease (low salt) or urinary stones (high salt), most diets have a similar salt content.

It is also possible for potassium bromide levels in blood to increase if a dog becomes severely dehydrated, such as after severe or bloody diarrhoea. Potassium bromide may need to be temporarily withdrawn or reduced if your dog appears more sedated.

Due to its long half-life, a one-off missed dose of potassium bromide is not too concerning. Nonetheless, potassium bromide therapy should not be abruptly interrupted otherwise a pet may have withdrawal symptoms.

Why do you need to take blood samples?

It is recommended to assess potassium bromide blood concentrations 8-16 weeks after starting the medication. It takes 4 months for blood levels to stabilise after the drug is started, so blood levels should be measured around 16 weeks after treatment begins. An ideal concentration is 1000 mg/l (15 mmol/l) to 2000 mg/l (25 mmol/l). It is acceptable to have higher blood concentrations if they do not have adverse effects, such as sedation.

Similarly, potassium bromide levels should be monitored every 6-12 months, 8-16 weeks after a dose change, and if control breaks down (i.e. unexpected seizures). It is common for veterinarians to attempt to measure potassium bromide levels in the blood just before the next dose is due. There is no need for these trough concentrations, however. Nevertheless, it is good practice to always:

1. Test samples in the same laboratory
2. Take a blood sample after medication at the same time
3. Fast a pet for at least 12 hours before taking a blood sample. The potassium bromide assay cannot be performed if there is excessive lipaemia (fat in the blood).

When potassium bromide serum concentrations exceed 1500 mg/l (20 mmol/l) and seizures remain uncontrolled (clusters of >3 seizures or seizures occurring more frequently than every 6 weeks), you may need to add or change the drug.

What side effects can Potassium bromide cause?

• Sedation and poor co-ordination – This is may be seen at the start of therapy, after increases in doses, or with the addition of another drug (especially phenobarbitone). In most cases, this effect wears off within a week. You may need to recommend reducing the potassium bromide dose or switching the pet to another drug if it doesn’t, or if it is too high. When the dog is drowsy soon after dosing, advise giving the medication at the end of the day. A split dose can also reduce sedation in some dogs, e.g. twice daily administration.
• Increased urination and drinking – Potassium bromide acts like a diuretic. You must recommend the pet has access to water at all times if they are receiving potassium bromide. In some cases, animals on high doses may wet the house overnight or after being left for an extended period of time.
• Increased appetite – The pet is likely to have an increased appetite when they are on potassium bromide therapy, however this does not mean they require more food. It is often difficult to avoid weight gain in dogs on KBr. Feeding a low-calorie food may help the pet eat more while not gaining weight. Using a Bustercube may also be useful for extending mealtimes.
• Gastrointestinal disease (vomiting and diarrhoea) – Also see pancreatitis below. It is recommended to mix potassium bromide with food since it is a gastrointestinal irritant. If the dog is not able to tolerate it, you may decide to try a different form, such as liquid rather than tablets.
• Pancreatitis – Epileptic dogs are at greater risk of pancreatitis i.e. inflammation of the pancreas. In severe cases, pancreatitis can cause vomiting and anorexia, which can be life-threatening. Several risk factors are likely to contribute to this disease, including obesity, persistently high resting triglycerides, high fat diets, the tendency to scavenge, and high dosages of phenobarbitone combined with KBr.
• Skin disease – In humans potassium bromide may cause skin changes – so called bromism – and this is one of the reasons this drug in not used for people. Dogs do not seem to suffer from this syndrome; however, dogs who have pre-existing skin conditions, for instance, atopy, may be itchier and may not be advised to take potassium bromide.
• Liver function – Potassium bromide does not require liver metabolism and is one of the few liver safe anti-epileptic drugs.
• Kidney function – Kidney function may also affect potassium bromide elimination. Unless your pet develops acute kidney failure, this is not a problem. The kidneys shut down in this situation, resulting in a rise of potassium bromide concentrations that anaesthetises the pet. To flush the potassium bromide out of the dog’s circulation, you may need to give fluids and diuretics. It is not possible to damage the kidneys by taking potassium bromide.  
• Cats and potassium bromide – Potassium bromide results in lung disease in 50% of cats that receive it and therefore is not a recommended therapy for this species.