Pharmacology. Phenobarbital is a barbiturate commonly used as an anticonvulsant. Because of the delay in onset of the therapeutic effect of phenobarbital, diazepam (See Benzodiazepines (Diazepam, Lorazepam, and Midazolam)) is usually the initial agent for parenteral anticonvulsant therapy. After an oral dose of phenobarbital, peak brain concentrations are achieved within 10–15 hours. Onset of effect after intravenous administration usually occurs within 5 minutes, although peak effects may take up to 30 minutes. Therapeutic plasma levels are 15–35 mg/L. The drug is eliminated by metabolism and renal excretion, and the elimination half-life is 48–100 hours.

Indications

1. 
   

   Control of tonic-clonic seizures and status epilepticus, generally as a second- or third-line agent after diazepam or phenytoin has been tried. Note: For treatment of drug-induced seizures, especially seizures caused by theophylline, phenobarbital often is tried before phenytoin.

   
   
2. 
   

   Management of withdrawal from ethanol and other sedative-hypnotic drugs.

Contraindications

1. 
   

   Known sensitivity to barbiturates.

   
   
2. 
   

   Manifest or latent porphyria.

Adverse effects

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