Phenobarbital is a barbiturate, a highly addictive, sedating drug that depresses the nervous system. It is usually prescribed to prevent seizures or to relieve anxiety. Phenobarbital is used to treat epilepsy and other seizure disorders since the drug stabilizes electrical activity in the brain. This test is used to measure and monitor the amount of phenobarbital in the blood and to determine whether the drug level is within a therapeutic range. Side effects from phenobarbital may include: drowsiness, headache, dizziness, depression, excitement (especially in children), upset stomach, and vomiting. TOO LOW levels are associated with seizures or anxiety. TOO HIGH levels might cause toxicity.
Peak level is variable, but usually 4-10 hours after the dose. The steady state concentration is at 5-20 days. Sampling time should be within this time frame.