What is phenobarbital used for?

Phenobarbital belongs to a group of drugs called barbiturates. It is used to treat seizures and provide relief from anxiety. It is also used to treat people struggling with barbiturate drug abuse. Such individuals can experience withdrawal symptoms when attempting to quit drug use. Phenobarbital reduces withdrawal symptoms during acute withdrawal from another barbiturate drug. 

How does phenobarbital work? 

Phenobarbital works by slowing brain activity in people with seizure disorders. Specifically, it acts on GABA receptors in the central nervous system to increase the seizure threshold and stop the spread of the seizure activity from the seizure focus to other parts of the brain. Phenobarbital has sedative, hypnotic effects and is used to induce sleep and relieve anxiety. 

When withdrawal symptoms occur in people with a physical dependence on barbiturates, doctors sometimes substitute phenobarbital, a long-acting barbiturate, for the addicting drug and subsequently withdraw the patient from phenobarbital. Because phenobarbital has a longer action, it provides more constant blood levels of a barbiturate compared to other shorter-acting barbiturates. This allows a person with physical dependence on a barbiturate to safely withdraw from drug abuse using smaller daily doses of barbiturates during withdrawal.

What are phenobarbital doses?

Phenobarbital is available in tablets (15 mg, 16.2 mg, 30 mg, 32.4 mg, 60 mg, 64.8 mg, 97.2 mg, and 100 mg) as well as 20 mg/5 mL elixir (liquid form). 

The usual phenobarbital dose for seizure control is 50 mg to 100 mg by mouth 2-3 times a day. The maximum daily dose of phenobarbital should not exceed 400 mg. Your doctor will adjust your phenobarbital dose based on the blood levels of the medication and its effectiveness in seizure control. An intravenous loading dose of 15-20 mg/kg may be used to treat status epilepticus. 

In children, this seizure medication is given based on body weight at 3-6 mg/kg/day (approximately 15 to 50 mg by mouth 2-3 times a day). 

For sedation, the usual phenobarbital dose is 30 mg to 120 mg per day, given in 2-3 divided doses.