Phenobarbital is a barbiturate commonly prescribed to manage epilepsy in dogs, and can also be used to prevent other nervous system incidents, including strokes. It is a common and inexpensive drug, and easy to administer. But it does have some potential side effects, both minor and major. With monitoring and an awareness of your dog's normal behavior, a dog's life can be comfortable and rewarding, even for prolonged periods on the medication.
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Liver Damage
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The most dangerous side effect of phenobarbital use is potential liver damage. Although it happens rarely, liver scarring and failure can occur. Symptoms of liver damage include weight loss, vomiting and diarrhea. Increased urination and increased appetite are occasional symptoms as well, but are common side effects of phenobarbital itself (not just liver damage), so it can be difficult to tell the difference.
Liver Damage Prevention
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Monitoring your dog's blood levels proactively can help identify liver damage before it is dangerous. Standard chemistry panels are recommended by most vets, as they test the enzymes ALT, GGT and alkaline phosphatase. Bile acid testing can also be useful in early identification of phenobarbital-related liver damage. Whatever tests you decide to have run on your dog, regular phenobarbital use should be accompanied by testing at least twice a year and possibly more often depending on the dosage.
Treatment
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Dogs who are showing signs of liver damage may still be able to continue with phenobarbital to prevent seizures. The addition of potassium bromide or milk thistle into their regimen, along with the reduction of phenobarbital, can help nullify some of the damaging effects phenobarbital has on the liver. This does have the risk of causing the recurrence of seizures, and should be done under a veterinarian's supervision.
Short-Term Side Effects
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When beginning a phenobarbital regimen, dog owners will often notice unusual behaviors. As phenobarbital affects brain chemistry, many early side effects are neurological, as the brain adjusts to a new chemical balance. A dog might seem restless and overexcited or, on the other end of the scale, lazy and sedated. Coordination can also be affected, and dogs new to phenobarbital may find stairs difficult for a short period of time. These side effects tend to diminish over a few weeks.
Long-Term Side Effects
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Increased appetite and thirst is a very common effect of phenobarbital. These symptoms can lead directly to weight gain and excessive urination. An exercise regimen should be enacted to allow the dog to eat until it is satisfied, and allow it to avoid any secondary health concerns which may be caused by weight gain. As for the urination, frequent walks are useful for addressing both urination and weight gain. Your dog may occasionally have bladder-control problems, particularly overnight.
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