Phenobarbital
Phenobarbital (Solfoton)
Phenobarbital
(fee-no- BAR-bih-tal)
Pregnancy Category: D Barbilixir Solfoton (C-IV) (Rx)
Phenobarbital sodium
Phenobarbital sodium (Luminal Sodium)
Phenobarbital
(fee-no- BAR-bih-tal)
Pregnancy Category: D Luminal Sodium (C-IV) (Rx)

Classification: Sedative, anticonvulsant, barbiturate type

Action/Kinetics: Depressant and anticonvulsant effects may be related to its ability to increase and/or mimic the inhibitory activity of GABA on nerve synapses. Is not an analgesic; not to be given to relieve pain. Long-acting. t 1/2: 53-140 hr. Onset: 30 to more than 60 min. Duration: 10-16 hr. Anticonvulsant therapeutic serum levels: 15-40 mcg/mL. Time for peak effect, after IV: up to 15 min. Distributed more slowly than other barbiturates due to lower lipid solubility. Is 50%-60% protein bound. Twenty-five percent eliminated unchanged in the urine.

Uses: PO: Sedative, hypnotic (short-term), anticonvulsant (partial and generalized tonic-clonic or cortical focal seizures); emergency control of acute seizure disorders such as status epilepticus, meningitis, tetanus, eclampsia, toxicity of local anesthetics. Parenteral: Sedative, hypnotic (short-term), preanesthetic, anticonvulsant, emergency control of acute seizure disorders.

Contraindications: Hypersensitivity to barbiturates, severe trauma, pulmonary disease when dyspnea or obstruction is present, edema, uncontrolled diabetes, history of porphyria, and impaired liver function and for clients in whom they produce an excitatory response. Also, clients who have been addicted previously to sedative-hypnotics.

Special Concerns: Use with caution during lactation and in clients with CNS depression, hypotension, marked asthenia (characteristic of Addison's disease, hypoadrenalism, and severe myxedema), porphyria, fever, anemia, hemorrhagic shock, cardiac, hepatic or renal damage, and a history of alcoholism in suicidal clients. Geriatric clients usually manifest increased sensitivity to barbiturates, as evidenced by confusion, excitement, mental depression, and hypothermia. Reduce the dose in geriatric and debilitated clients, as well as those with impaired hepatic or renal function. When given in the presence of pain, restlessness, excitement, and delirium may result.

Side Effects: CNS: Sleepiness, drowsiness, agitation, confusion, hyperkinesia, ataxia, CNS depression, nightmares, nervousness, psychiatric disturbances, hallucinations, insomnia, anxiety, dizziness, headache, abnormal thinking, vertigo, lethargy, hangover, excitement, appearance of being inebriated. Irritability and hyperactivity in children. Musculoskeletal: Localized or diffuse myalgic, neuralgic, or arthritic pain, especially in psychoneurotic clients. Pain is often most intense in the morning and is frequently located in the neck, shoulder girdle, and arms. Respiratory: Hypoventilation, apnea, respiratory depression. CV: Bradycardia, hypotension, syncope, circulatory collapse. GI: N&V;, constipation, liver damage (especially with chronic use of phenobarbital). Allergic: Skin rashes, angioedema exfoliative dermatitis (including Stevens-Johnson syndrome and toxic epidermal necrolysis). Allergic reactions are most common in clients who have asthma, urticaria, angioedema, and similar conditions. Symptoms include localized swelling (especially of the lips, cheeks, or eyelids) and erythematous dermatitis).
After IV use. CV: Circulatory depression, thrombophlebitis, peripheral vascular collapse, seizures with cardiorespiratory arrest, myocardial depression, cardiac arrhythymias. Respiratory: Apnea, laryngospasm, bronchospasm dyspnea, rhinitis, sneezing, coughing. CNS: Emergence delirium, headache, anxiety, prolonged somnolence and recovery, restlessness, seizures. GI: N&V;, abdominal pain, diarrhea, cramping. Hypersensitivity: Acute allergic reactions, including erythema, pruritus, anaphylaxis. Miscellaneous: Pain or nerve injury at injection site, salivation, hiccups, skin rashes, shivering, skeletal muscle hyperactivity, immune hemolytic anemia with renal failure and radial nerve palsy.
After IM use: Pain at injection site.
Although barbiturates can induce physical and psychologic dependence if high doses are used regularly for long periods of time, the incidence of dependence on phenobarbital is low. Withdrawal symptoms usually begin after 12-16 hr of abstinence. Manifestations of withdrawal include anxiety, weakness, N&V;, muscle cramps, delirium, and even tonic-clonic seizures. Chronic use may result in headache, fever, and megaloblastic anemia.

Laboratory Test Alterations: Interference with test method: 17-Hydroxycorticosteroids. Creatinine phosphokinase, alkaline phosphatase, serum transaminase, serum testosterone (in certain women), urinary estriol, porphobilinogen, coproporphyrin, uroporphyrin. PT in clients on coumarin. or Bilirubin. False + lupus erythematosus test.

Overdose Management: Symptoms (Acute Toxicity): Characterized by cortical and respiratory depression; anoxia; peripheral vascular collapse; feeble, rapid pulse; pulmonary edema; decreased body temperature; clammy, cyanotic skin; depressed reflexes; stupor; and coma. After initial constriction the pupils become dilated. Death results from respiratory failure or arrest followed by cardiac arrest. Symptoms (Chronic Toxicity): Prolonged use of barbiturates at high doses may lead to physical and psychologic dependence, as well as tolerance. Symptoms of dependence are similar to those associated with chronic alcoholism, and withdrawal symptoms are equally severe. Withdrawal symptoms usually last for 5-10 days and are terminated by a long sleep. Treatment (Acute Toxicity): Maintenance of an adequate airway, oxygen intake, and carbon dioxide removal are essential. After PO ingestion, gastric lavage or gastric aspiration may delay absorption. Emesis should not be induced once the symptoms of overdosage are manifested, as the client may aspirate the vomitus into the lungs. Also, if the dose of barbiturate is high enough, the vomiting center in the brain may be depressed. Absorption following SC or IM administration of the drug may be delayed by the use of ice packs or tourniquets. Maintain renal function. Removal of the drug by peritoneal dialysis or an artificial kidney should be carried out. Supportive physiologic methods have proven superior to use of analeptics.
Treatment (Chronic Toxicity): Cautious withdrawal of the hospitalized addict over a 2-4-week period. A stabilizing dose of 200-300 mg of a short-acting barbiturate is administered q 6 hr. The dose is then reduced by 100 mg/day until the stabilizing dose is reduced by one-half. The client is then maintained on this dose for 2-3 days before further reduction. The same procedure is repeated when the initial stabilizing dose has been reduced by three-quarters. If a mixed spike and slow activity appear on the EEG, or if insomnia, anxiety, tremor, or weakness is observed, the dosage is maintained at a constant level or increased slightly until symptoms disappear.

Drug Interactions: GENERAL CONSIDERATIONS

1. Phenobarbital stimulates the activity of enzymes responsible for the metabolism of a large number of other drugs by a process known as enzyme induction. As a result, when phenobarbital is given to clients receiving such drugs, their therapeutic effectiveness may be markedly reduced or even abolished.

2. The CNS depressant effect of the barbiturates is potentiated by many drugs. Concomitant administration may result in coma or fatal CNS depression. Barbiturate dosage should either be reduced or eliminated when other CNS drugs are given.

3. Barbiturates also potentiate the toxic effects of many other agents.

Acetaminophen / Risk of hepatotoxicity when used with large or chronic doses of barbiturates Alcohol / Potentiation or addition of CNS depressant effects. Concomitant use may lead to drowsiness, lethargy, stupor, respiratory collapse, coma, or death Anesthetics, general / See Alcohol Anorexiants / Effect of anorexiants due to opposite activities Antianxiety drugs / See Alcohol Anticoagulants, oral / Effect of anticoagulants due to absorption from GI tract and breakdown by liver Antidepressants, tricyclic / Effect of antidepressants due to breakdown by liver Antidiabetic agents / Prolong the effects of barbiturates Antihistamines / See Alcohol Beta-adrenergic agents / Beta blockade due to breakdown by the liver Carbamazepine / Serum carbazepine levels may occur Charcoal / Absorption of barbiturates from the GI tract Chloramphenicol / Effect of barbiturates by breakdown by the liver and effect of chloramphenicol by breakdown by liver Clonazepam / Barbiturates may excretion of clonazepam loss of efficacy Clozapine / Clozapine plasma levels R/T liver metabolism CNS depressants / See Alcohol Corticosteroids / Effect of corticosteroids due to breakdown by liver Digitoxin / Effect of digitoxin due to breakdown by liver Doxorubicin / Effect of doxorubicin due to excretion Doxycycline / Effect of doxycycline due to breakdown by liver (effect may last up to 2 weeks after barbiturates are discontinued) Estrogens / Effect of estrogen due to breakdown by liver Felodipine / Plasma levels of felodipine effect Fenoprofen / Bioavailability of fenoprofen Furosemide / Risk or intensity of orthostatic hypotension Griseofulvin / Effect of griseofulvin due to absorption from GI tract Haloperidol / Effect of haloperidol due to breakdown by liver Indian snakeroot / Additive CNS depression Kava kava / Potentiation of CNS depression MAO inhibitors / Effect of barbiturates due to breakdown by liver Meperidine / CNS depressant effects may be prolonged Methadone / Effect of methadone Methoxyflurane / Kidney toxicity due to breakdown of methoxyflurane by liver to toxic metabolites Metronidazole / Effect of metronidazole Narcotic analgesics / See Alcohol Oral contraceptives / Effect of contraceptives due to breakdown by liver Phenothiazines / Effect of phenothiazines due to breakdown by liver; also see Alcohol Phenytoin / Effect variable and unpredictable; monitor carefully Procarbazine / Effect of barbiturates Quinidine / Effect of quinidine due to breakdown by liver Rifampin / Effect of barbiturates due to breakdown by liver Sedative-hypnotics, nonbarbiturate / See Alcohol Theophyllines / Effect of theophyllines due to breakdown by liver Valproic acid / Effect of barbiturates due to breakdown by liver Verapamil / Excretion of verapamil effect Vitamin D / Barbiturates may requirements for vitamin D due to breakdown by the liver

How Supplied: Phenobarbital: Elixir: 20 mg/5 mL; Tablet: 15 mg, 16.2 mg, 30 mg, 60 mg, 100 mg. Phenobarbital sodium: Injection: 30 mg/mL, 60 mg/mL, 65 mg/mL, 130 mg/mL

Dosage
Phenobarbital, Phenobarbital Sodium ?Capsules, Elixir, Tablets Sedation.
Adults: 30-120 mg/day in two to three divided doses. Pediatric: 2 mg/kg (60 mg/m ²) t.i.d.
Hypnotic.
Adults: 100-200 mg at bedtime. Pediatric: Dose should be determined by provider, based on age and weight.
Anticonvulsant.
Adults: 60-200 mg/day in single or divided doses. Pediatric: 3-6 mg/kg/day in single or divided doses.
?IM, IV Sedation.
Adults: 30-120 mg/day in two to three divided doses.
Preoperative sedation.
Adults: 100-200 mg IM only, 60-90 min before surgery. Pediatric: 1-3 mg/kg IM or IV 60-90 min prior to surgery.
Hypnotic.
Adults: 100-320 mg IM or IV.
Acute convulsions.
Adults: 200-320 mg IM or IV; may be repeated in 6 hr if needed. Pediatric: 4-6 mg/kg/day for 7-10 days to achieve a blood level of 10-15 mcg/mL (or 15 mg/kg/day, IV or IM).
Status epilepticus.
Adults: 15-20 mg/kg IV (given over 10-15 min); may be repeated if needed. Pediatric: 15-20 mg/kg given over a 10- to 15-min period.