What Effects does Phenobarbital have on Dogs and Cats?

By Tess Thompson

Phenobarbital is a long acting barbiturate that is the preferred medication for treating feline and canine epilepsy. Barbiturate is an organic compound that induces strong sleep and mental lethargy. An overdose can be lethal at times. It is relatively inexpensive and available in preparations that suit animals of all ages and weight. It is effective in treating a majority of dogs with idiopathic epilepsy. Despite of the fact that the drug is not being approved by the FDA, it is fairly acceptable among the practicing veterinarians. As Phenobarbital is commonly prescribed for treating epileptic feline and canine seizures its affect on the body is well documented.

The prescribed dosage is based on the individual’s response to the drug. This is because the speed with which it is absorbed and metabolized can vary with each dog. The dosage instructions on the label only serve as a guideline rather than a definite instruction. Mostly the lowest end of the dosage is recommended unless the patient has frequent or severe seizures.

Phenobarbital works by decreasing the neuron activity responsible for seizures. However, in the process it disturbs other neuronal activities as well. This disruption is mostly responsible for producing side effects when the drug is administered for the first time. These side effects include:

  • Sedation.
  • Lethargy.
  • Increased urination, thirst and appetite.
  • Hyperactivity or restlessness.
  • Loss of coordination in leg movement.

Many of these side effects disappear in a couple of weeks but increase urination thirst, and hunger may persist over a long time.

There are strong possibilities of long term administration of Phenobarbital for dogs with severe epilepsy. If the drug is used for more than three months it is likely to scar liver tissue and cause liver failure if not attended to in time. Timely intervention with a liver friendly diet can reverse liver damage. In certain cases the drug may have to be tapered down or discontinued to prevent permanent liver damage.

Phenobarbital is known to interact with certain antibiotics like chloramphenicol and doxycycline, corticosteroids and drugs used for treating parasitic and fungal infections in dogs. Phenobarbital causes an increase in liver activity when used in conjunction with these drugs. This causes them to metabolize quickly, which means a higher dose of these drugs may be required to achieve the desired results.

A therapeutic or controlled level of Phenobarbital should be maintained at all costs. Regular monitoring is also necessary. Blood work should be performed two weeks after beginning treatment. Thereafter, therapeutic levels should be checked every six months. Discontinuation is recommended only after seizures subside for a length of time of one to two years. Side effects may affect the animal’s quality of life, and in some cases cause severe liver damage. Potassium bromide can be considered as an alternative if treatment has must continue over long periods of time.

In most of the cases epilepsy is without a known cause (idiopathic) but can also be due to other reasons. If an underlying disease is identified, the disease should be treated first.



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