phenobarbital

phenobarbital

(fee noe bar' bi tal)

phenobarbital

Oral preparations:

Bellatal, Solfoton

phenobarbital sodium

Parenteral:

Luminal Sodium

Pregnancy Category D

Controlled Substance C-IV

Drug classes

Barbiturate (long acting)

Sedative

Hypnotic

Antiepileptic

Therapeutic actions

General CNS depressant; barbiturates inhibit impulse conduction in the ascending RAS, depress the cerebral cortex, alter cerebellar function, depress motor output, and can produce excitation, sedation, hypnosis, anesthesia, and deep coma; at subhypnotic doses, has antiseizure activity, making it suitable for long-term use as an antiepileptic.

Indications

·        Oral or parenteral: Sedative

·        Oral or parenteral: Hypnotic, treatment of insomnia for up to 2 wk

·        Oral: Long-term treatment of generalized tonic-clonic and cortical focal seizures

·        Oral: Emergency control of certain acute seizures (eg, those associated with status epilepticus, eclampsia, meningitis, tetanus, and toxic reactions to strychnine or local anesthetics)

·        Parenteral: Preanesthetic

·        Parenteral: Treatment of generalized tonic-clonic and cortical focal seizures

·        Parenteral: Emergency control of acute seizures (tetanus, eclampsia, epilepticus)

Contraindications and cautions

·        Contraindicated with hypersensitivity to barbiturates, manifest or latent porphyria; marked liver impairment; nephritis; severe respiratory distress; previous addiction to sedative-hypnotic drugs (may be ineffective and may contribute to further addiction); pregnancy (fetal damage, neonatal withdrawal syndrome).

·        Use cautiously with acute or chronic pain (drug may cause paradoxical excitement or mask important symptoms); seizure disorders (abrupt discontinuation of daily doses can result in status epilepticus); lactation (secreted in breast milk; drowsiness in nursing infants); fever, hyperthyroidism, diabetes mellitus, severe anemia, pulmonary or cardiac disease, status asthmaticus, shock, uremia; impaired liver or renal function, debilitation.

Available forms

Tablets—15, 16, 16.2, 30, 60, 90, 100 mg; capsules—16 mg; elixir—15 mg/5 mL, 20 mg/5 mL; injection—30, 60, 65, 130 mg/mL

Dosages

ADULTS

Oral

·        Sedation: 30–120 mg/day in two to three divided doses. No more than 400 mg per 24 hr.

·        Hypnotic: 100–200 mg hs.

·        Antiepileptic: 60–100 mg/day.

IM or IV

·        Sedation: 30–120 mg/day IM or IV in two to three divided doses.

·        Preoperative sedation: 100–200 mg IM, 60–90 min before surgery.

·        Hypnotic: 100–320 mg IM or IV.

·        Acute seizures: 200–320 mg IM or IV repeated in 6 hr if needed.

PEDIATRIC PATIENTS

Oral

·        Sedation: 2 mg/kg/dose PO tid. 8–32 mg/dose.

·        Hypnotic: Determine dosage using age and weight charts.

·        Antiepileptic: 3–6 mg/kg/day.

IM or IV

·        Preoperative sedation: 1–3 mg/kg IM or IV 60–90 min before surgery.

·        Antiepileptic: 4–6 mg/kg/day for 7–10 days to a blood level of 10–15 mcg/mL or 10–15 mg/kg/day IV or IM.

·        Status epilepticus: 15–20 mg/kg IV over 10–15 min.

GERIATRIC PATIENTS OR PATIENTS WITH DEBILITATING DISEASE OR RENAL OR HEPATIC IMPAIRMENT

Reduce dosage and monitor closely—may produce excitement, depression, confusion.

Pharmacokinetics

Route	Onset	Duration
Oral	30–60 min	10–16 hr
IM, SC	10–30 min	4–6 hr
IV	5 min	4–6 hr

Metabolism: Hepatic; T_1/2: 79 hr

Distribution: Crosses placenta; enters breast milk

Excretion: Urine

IV facts

Preparation: No further preparation is needed.

Infusion: Infuse very slowly, each 60 mg over 1 min, directly IV or into tubing or running IV; inject partial dose and observe for response before continuing. It may require > 15 min to achieve peak levels in brain tissue. Avoid overdosing by observing effects before continued dosing.

Incompatibilities: Do not combine with chlorpromazine, codeine, ephedrine, hydralazine, hydrocortisone, insulin, meperidine, methadone, procaine, promazine,vancomycin.

Adverse effects

·        CNS: Somnolence, agitation, confusion, hyperkinesia, ataxia, vertigo, CNS depression, nightmares, lethargy, residual sedation (hangover), paradoxical excitement, nervousness, psychiatric disturbance, hallucinations, insomnia, anxiety, dizziness, thinking abnormality

·        CV: Bradycardia, hypotension, syncope

·        GI: Nausea, vomiting, constipation, diarrhea, epigastric pain

·        Hypersensitivity: Rashes, angioneurotic edema, serum sickness, morbiliform rash, urticaria; rarely, exfoliative dermatitis, Stevens-Johnson syndrome

·        Local: Pain, tissue necrosis at injection site, gangrene; arterial spasm with inadvertent intra-arterial injection; thrombophlebitis; permanent neurologicdeficit if injected near a nerve

·        Respiratory: Hypoventilation, apnea, respiratory depression, laryngospasm, bronchospasm, circulatory collapse

·        Other: Tolerance, psychological and physical dependence, withdrawal syndrome

Interactions

Drug-drug

·        Increased serum levels and therapeutic and toxic effects with valproic acid

·        Increased CNS depression with alcohol

·        Increased risk of nephrotoxicity with methoxyflurane

·        Increased risk of neuromuscular excitation and hypotension with barbiturate anesthetics

·        Decreased effects of the following drugs: Theophyllines, oral anticoagulants, beta-blockers, doxycycline, corticosteroids, hormonal contraceptives and estrogens, metronidazole, phenylbutazones, quinidine, felodipine, fenoprofen

Nursing considerations

Assessment

·        History: Hypersensitivity to barbiturates, manifest or latent porphyria; marked liver impairment; nephritis; severe respiratory distress; previous addiction to sedative-hypnotic drugs; pregnancy; acute or chronic pain; seizure disorders; lactation, fever; hyperthyroidism; diabetes mellitus; severe anemia; cardiac disease; shock; uremia; impaired liver or renal function; debilitation

·        Physical: Weight; T; skin color, lesions; orientation, affect, reflexes; P, BP, orthostatic BP; R, adventitious sounds; bowel sounds, normal output, liver evaluation; LFTs, renal function tests, blood and urine glucose, BUN

Interventions

·        Monitor patient responses, blood levels (as appropriate) if any interacting drugs listed above are given with phenobarbital; suggest alternative means of contraception to women using hormonal contraceptives.

·        WARNING: Do not give intra-arterially; may produce arteriospasm, thrombosis, gangrene.

·        Administer IV doses slowly.

·        Administer IM doses deep in a large muscle mass (gluteus maximus, vastus lateralis) or other areas where there is little risk of encountering a nerve trunk or major artery.

·        WARNING: Monitor injection sites carefully for irritation, extravasation (IV use). Solutions are alkaline and very irritating to the tissues.

·        Monitor P, BP, respiration carefully during IV administration.

·        Arrange for periodic lab tests of hematopoietic, renal, and hepatic systems during long-term therapy.

·        WARNING: Taper dosage gradually after repeated use, especially in patients with epilepsy. When changing from one antiepileptic drug to another, taper dosage of the drug being discontinued while increasing the dosage of the replacement drug.

Teaching points

·        This drug will make you drowsy and less anxious; do not try to get up after you have received this drug (request assistance to sit up or move around).

·        Take this drug exactly as prescribed; this drug is habit forming; its effectiveness in facilitating sleep disappears after a short time.

·        Do not take this drug longer than 2 weeks (for insomnia), and do not increase the dosage without consulting the prescriber.

·        Do not reduce the dosage or discontinue this drug (when used for epilepsy); abrupt discontinuation could result in a serious increase in seizures.

·        Wear a medical alert tag so that emergency medical personnel will know you have epilepsy and are taking this medication.

·        Avoid pregnancy while taking this drug; use a means of contraception other than hormonal contraceptives.

·        You may experience these side effects: Drowsiness, dizziness, hangover, impaired thinking (may lessen after a few days; avoid driving or engaging in dangerous activities); GI upset (take drug with food); dreams, nightmares, difficulty concentrating, fatigue, nervousness (reversible).

·        Report severe dizziness, weakness, drowsiness that persists, rash or skin lesions, fever, sore throat, mouth sores, easy bruising or bleeding, nosebleed,petechiae, pregnancy.

Adverse effects in Italic are most common; those in Bold are life-threatening.