Details About Overdose or Poisoning Generic Salt :: Phenobarbital
Drug Pharmacology ::
I. Pharmacology. Phenobarbitalis a barbiturate commonly used as an anticonvulsant. Because of thedelay in onset of the therapeutic effect of phenobarbital, diazepam(see Benzodiazepines [Diazepam, Lorazepam, and Midazolam]) is usuallythe initial agent for parenteral anticonvulsant therapy. After an oraldose of phenobarbital, peak brain concentrations are achieved within10–15 hours. Onset of effect after intravenous administration usuallyoccurs within 5 minutes, although peak effects may take up to 30minutes. Therapeutic plasma levels are 15–35 mg/L. The drug iseliminated by metabolism and renal excretion, and the eliminationhalf-life is 48–100 hours.
Drug Indications ::
Controlof 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 bytheophylline, phenobarbital often is tried before phenytoin.
Management of withdrawal from ethanol and other sedative-hypnotic drugs.
Drug Contra-Indications ::
Known sensitivity to barbiturates.
Manifest or latent porphyria.
Drug Adverse Effects ::
IV. Adverse effects
Central nervous system depression, coma, and respiratory arrest may result, especially with rapid bolus or excessive doses.
Hypotensionmay result from rapid intravenous administration. This can be preventedby limiting the rate of administration to less than 50 mg/min(children, 1 mg/kg/min).
Use in pregnancy. FDAcategory D (possible fetal risk). Phenobarbital readily crosses theplacenta, and chronic use may cause hemorrhagic disease of the newborn(owing to vitamin K deficiency) or neonatal dependency and withdrawalsyndrome. However, these potential effects do not preclude its acute,short-term use in a seriously symptomatic patient (see Table III–1).
Drug Lab Interactions ::
Drug or laboratory interactions
Phenobarbital has additive CNS and respiratory depression effects with other sedative drugs.
Hepatic enzyme induction with chronic use, although this is not encountered with acute phenobarbital dosing.
Extracorporealremoval techniques (eg, hemodialysis, hemoperfusion, and repeat-doseactivated charcoal; see Activated charcoal) may enhance the clearanceof phenobarbital, possibly requiring supplemental dosing to maintaintherapeutic levels.
Drug Dose Management ::
Dosage and method of administration
Parenteral. Administer slowly intravenously (rate 50 mg/min; children, 1mg/kg/min) until seizures are controlled or the loading dose of 10–15mg/kg is achieved. For status epilepticus, give 15–20 mg/kg IV over10–15 minutes, not to exceed 100 mg/minute (children have required asmuch as 30 mg/kg in the first 24 hours to treat status epilepticus).Slow the infusion rate if hypotension develops. Intermittent infusionsof 2 mg/kg every 5–15 minutes may diminish the risk of respiratorydepression or hypotension. For alcohol withdrawal seizures, initialdose of 260 mg, then 130 mg every 30 minutes until signs of mildintoxication (see below).
1. Ifintravenous access is not immediately available, phenobarbital may begiven intramuscularly; the initial dose in adults and children is 3–5mg/kg IM.
2. It may also be given by the intraosseous route.
Oral. Fortreatment of barbiturate or sedative drug withdrawal, give 60–120 mgorally and repeat every hour until signs of mild intoxication appear(eg, slurred speech, drowsiness, and nystagmus).
Drug Chemical Formulations ::
Parenteral. Phenobarbital sodium (Luminal and others), 30, 60, 65, and 130 mg/mL in 1-mL Tubex syringes, vials, and ampules.
Oral. 15-, 16-, 30-, 60-, 90-, and 100-mg tablets; 16-mg capsule; also elixir (15 and 20 mg/5 mL).
The suggested minimum stocking level to treat a 70-kg adult for the first 24 hours is 16 ampules (130 mg each) or the equivalent.