Phenobarbital is one of the most popular anticonvulsant medications used in the veterinary field today. It is often prescribed to treat canines and felines that are suffering from seizures. It is most commonly used as a lone therapy, but in cases where the medication is not having the desired effect, it can be combined with other anticonvulsants like Zonisamide.

Phenobarbital is highly effective as a treatment for epilepsy, because it decreases and stabilizes the neuron activity in the pet’s brain. More precisely, Phenobarbital increases the activity in the GABA neurotransmitter, thus improving its nerve-calming properties, while at the same time reducing the activity in the Glutamate neurotransmitter and thereby reducing its nerve-stimulating properties. These actions can significantly reduce the number of episodes that a pet experiences.

Precautions and Side Effects of Phenobarbital

Because Phenobarbital is so effective at decreasing the activity in the Glutamate neurotransmitter in the brain, it also has the potential to decrease the activity in other neurons. This will sometimes result in lethargy and other unwanted side effects. As a result, it is crucial to monitor a pet very closely while they are being treated with this medication.

Most commonly, side effects (if the pet has any) are experienced in the first few weeks of starting the medication, or when the dosage is increased. These can include anxiety, depression, or agitation. In rarer cases, ataxia and sedation can also occur. In most cases, once the pet becomes acclimated to the medication, the side effects will diminish over time.

Other potential side effects of Phenobarbital include polyuria, polydipsia, polyphagia, weight gain, thrombocytopenia, changes in liver function, neutropenia, and anemia. Immune-mediated reactions and bone marrow hypoplasia can also occur, but these tend to be very rare instances.

Phenobarbital Considerations

There are some instances in which Phenobarbital should be closely guarded. It should be administered with extreme caution in pets diagnosed with hypovolemia, kidney disease, anemia, and/or hypoadrenocorticism. Use of the medication should be avoided outright in pets with severe respiratory dysfunction, liver disease, or those with a known sensitivity to other anti-seizure medications.

Phenobarbital can also negatively affect the effectiveness of other medications, including certain anticoagulants, beta blockers, estrogen agents, progestins, corticosteroids, and tricyclic antidepressants. Meanwhile, certain drugs can actually increase the effect of Phenobarbital. These include phenothiazine opiate agonists, CNS depressants, and antihistamines.

Dosage and Administration of Phenobarbital

The dosage and method of administration for Phenobarbital should always be directed by your veterinarian, and their instructions should be explicitly followed. This medication is available in a variety of formulations, including oral tablet and injectable versions. Dosage is determined based on several different factors, including the pet’s species, breed, size, and age.

Author: Giano Panzarella