Pharmacologic class: Barbiturate
Therapeutic class: Anxiolytic, anticonvulsant, sedative-hypnotic
Controlled substance schedule IV Pregnancy risk category D
Interferes with gamma-aminobutyric acid receptors, blocking nerve impulse transmission in CNS, which reduces motor activity and raises seizure threshold
Capsules: 16 mg
Elixir: 15 mg/5 ml, 20 mg/5 ml
Injection: 30 mg/ml and 60 mg/ml in 1-ml prefilled syringes; 65 mg/ml in 1-ml vials; 130 mg/ml in 1-ml prefilled syringes, 1-ml vials, and 1-ml ampules
Tablets: 15 mg, 16 mg, 30 mg, 60 mg, 90 mg, 100 mg
⊘Indications and dosages
➣ Tonic-clonic (grand mal) and partial seizures; febrile seizures in children
Adults: 60 to 100 mg/day P.O. as a single dose or in two or three divided doses; or initially, 100 to 320 mg I.V. p.r.n. (a total of 600 mg I.V. in a 24-hour period).
Infants and children: Loading dose of 15 to 20 mg/kg P.O. (produces drug blood level of 20 mcg/ml shortly after dosing). To achieve therapeutic blood level (10 to 25 mcg/ml), children usually need higher dosage/kg than adults. Follow loading dose with 3 to 6 mg/kg/day P.O. Alternatively, 4 to 6 mg/kg/day I.M. or I.V. for 7 to 10 days to achieve blood level of 10 to 15 mcg/ml.
➣ Status epilepticus
Adults: 200 to 320 mg I.M. or I.V., repeated q 6 hours p.r.n.
Children: 15 to 20 mg/kg I.V. given over 10 to 15 minutes
➣ Sedation or hypnotic effect
Adults: For sedation, 30 to 120 mg/day P.O. or 30 to 120 mg/day I.M. or I.V. in two or three divided doses. As a hypnotic, 100 to 200 mg P.O. or 100 to 320 mg I.M. or I.V. at bedtime. Don't exceed 400 mg in a 24-hour period.
➣ Preoperative sedation
Adults: 100 to 200 mg I.M. 60 to 90 minutes before surgery
Children: 1 to 3 mg/kg I.M. or I.V., as prescribed.
• Impaired hepatic or renal function
• Elderly or debilitated patients
• Prevention and treatment of hyperbilirubinemia
• Hypersensitivity to drug or other barbiturates
• Manifest or latent porphyria
• Nephritis (with large doses)
• Severe respiratory disease with dyspnea or obstruction
• History of sedative-hypnotic abuse
• Subcutaneous or intra-arterial administration
Use cautiously in:
• hepatic dysfunction, renal impairment, seizure disorder, fever, hyperthyroidism, diabetes mellitus, severe anemia, pulmonary or cardiac disease
• history of suicide attempt or drug abuse
• chronic phenobarbital use
• elderly or debilitated patients
• pregnant or breastfeeding patients
• children younger than age 6.
• Inject I.M. deep into large muscle mass; limit volume to 5 ml.
☞ Give I.V. no faster than 60 mg/minute. Keep resuscitation equipment at hand.
• Stop injection immediately if patient complains of pain or if circulation at injection site diminishes (indicating inadvertent intra-arterial injection).
☞ Don't give by subcutaneous route; severe reactions (such as pain and tissue necrosis) may occur.
☞ Know that when given I.V. for status epilepticus, drug may take 15 minutes to attain peak blood level in brain. If injected continuously until seizures stop, drug brain level would keep rising and could exceed that required to control seizures. To avoid barbiturate-induced depression, use minimal amount required and wait for anticonvulsant effect to occur before giving second dose.
• Use parenteral route only when patient can't receive drug P.O.
• Know that drug is intended only for short-term use, losing efficacy after about 2 weeks.
CNS: headache, dizziness, anxiety, depression, drowsiness, excitation, delirium, lethargy, agitation, confusion, hyperkinesia, ataxia, vertigo, nightmares, nervousness, paradoxical stimulation, abnormal thinking, hallucinations, insomnia, CNS depression
CV: hypotension, syncope, bradycardia (with I.V. use)
GI: nausea, vomiting, constipation
Hematologic: megaloblastic anemia
Hepatic: hepatic damage
Musculoskeletal: joint pain, myalgia
Respiratory: hypoventilation, laryngospasm, bronchospasm, apnea (with I.V. use); respiratory depression
Skin: rash, urticaria, exfoliative dermatitis, Stevens-Johnson syndrome
Other: phlebitis at I.V. site, drug dependence, hypersensitivity reactions including angioedema
Drug-drug.Acetaminophen: increased risk of hepatotoxicity
Activated charcoal: decreased phenobarbital absorption
Anticoagulants, beta-adrenergic blockers (except timolol), carbamazepine, clonazepam, corticosteroids, digoxin, doxorubicin, doxycycline, felodipine, fenoprofen, griseofulvin, hormonal contraceptives, metronidazole, quinidine, theophylline, verapamil: decreased efficacy of these drugs
Chloramphenicol, hydantoins, narcotics: increased or decreased effects of either drug
Cyclophosphamide: increased risk of hematologic toxicity
Divalproex, MAO inhibitors, valproic acid: decreased phenobarbital metabolism, increased sedative effect Other CNS depressants (including first-generation antihistamines, opioids, other sedative-hypnotics): additive CNS depression
Rifampin: increased phenobarbital metabolism and decreased effects
Drug-diagnostic tests.Bilirubin: decreased level in neonates and patients with seizure disorders or congenital nonhemolytic unconjugated hyperbilirubinemia
Drug-herbs.Chamomile, hops, kava, skullcap, valerian: increased CNS depression
St. John's wort: decreased drug effects
Drug-behaviors.Alcohol use: additive CNS effects
• Monitor vital signs; watch for bradycardia and hypotension.
☞ In patients with seizure disorders, know that drug withdrawal may cause status epilepticus.
• Assess neurologic status. Institute safety measures as needed.
☞ Closely monitor respiratory status, especially for respiratory depression and airway spasm.
• Monitor phenobarbital blood level, CBC, and kidney and liver function tests.
• Watch for signs of drug dependence.
☞ Instruct patient to promptly report rash, facial and lip edema, syncope, dyspnea, or depression.
☞ Stress importance of taking exactly as prescribed, with or without food. Caution patient not to stop therapy abruptly, especially if he's taking drug for seizures.
• Tell patient that prolonged use may lead to dependence.
• Instruct patient to seek medical advice before taking other prescription or over-the-counter drugs.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects him.
• Advise patient to avoid herbs, alcohol, and other CNS depressants.
• Instruct patient taking hormonal contraceptives to use alternate birth-control method.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, herbs, and behaviors mentioned above.