The Importance of a Phenobarbital Blood Test

Seizure disorders occur in pets just as they occur in people, and the most commonly used drug to control seizures is phenobarbital. However, administering the proper dose to reduce the incidence of seizures without overdosing is key. So the phenobarbital blood level must be monitored carefully when used for treatment. A phenobarbital level is indicated after trying a new dose of phenobarbital, if seizures develop during phenobarbital treatment, or if signs of liver disease develop while a pet is on the drug. It is also a good idea to check phenobarbital blood levels at least every 6 months, even if the pet is doing well.

There are no real contraindications to performing this test in an animal on phenobarbital.

What Does a Phenobarbital Level Reveal?

A phenobarbital level will reveal the levels of phenobarbital circulating in the blood. There is a specific amount that is considered safe and therapeutic.

High levels of phenobarbital indicate that the dose should be reduced. If seizures continue or liver abnormalities occur, additional medications should be prescribed. Low levels indicate that the dose of phenobarbital should be increased in order to be effective.

How Is a Phenobarbital Level Done?

In order to perform a phenobarbital level, your veterinarian must draw a blood sample, which is placed in a special glass tube. The blood sample is allowed to clot, and is then placed in a centrifuge, where it is divided into two parts: serum and a blood clot. The serum is removed and submitted to a laboratory for analysis. The blood clot is discarded. Most often, the blood sample is submitted to an outside laboratory for evaluation. Test results may not be available for up to 1 to 2 days.

Is a Phenobarbital Level Painful?

Any pain involved is associated with the collection of the blood sample, since a needle is used to pierce the skin and enter a blood vessel to draw the sample. As with people, the pain experienced from a needle will vary from individual to individual.

Is Sedation or Anesthesia Needed for a Phenobarbital Level?

Neither sedation nor anesthesia is needed in most patients; however, some pets resent needle sticks and may need tranquilization or ultrashort anesthesia.