Classifications:central nervous system agent; anticonvulsant; sedative-hypnotic; barbiturate
Pregnancy Category: D
15 mg, 16 mg, 16.2 mg, 30 mg, 60 mg, 90 mg, 100 mg tablets; 16 mg capsules; 15 mg/5 mL, 20 mg/5 mL liquid; 30 mg/mL, 60 mg/mL, 65 mg/mL, 130 mg/mL injection
Long-acting barbiturate. Sedative and hypnotic effects of barbiturates appear to be due primarily to interference with impulse transmission of cerebral cortex by inhibition of reticular activating system. CNS depression may range from mild sedation to coma, depending on dosage, route of administration, degree of nervous system excitability, and drug tolerance. Initially, barbiturates suppress REM sleep, but with chronic therapy REM sleep returns to normal.
Produces sedative and hypnotic effects with no analgesic properties, and small doses may increase reaction to painful stimuli. Phenobarbital limits spread of seizure activity by increasing threshold for motor cortex stimuli. Barbiturates are habit forming.
Long-term management of tonic-clonic (grand mal) seizures and partial seizures; status epilepticus, eclampsia, febrile convulsions in young children. Also used as a sedative in anxiety or tension states; in pediatrics as preoperative and postoperative sedation and to treat pylorospasm in infants.
Sensitivity to barbiturates; manifest hepatic or familial history of porphyria; severe respiratory or kidney disease; history of previous addiction to sedative hypnotics; uncontrolled pain; pregnancy (particularly early pregnancy) (category D), lactation; sustained release formulation for children < 12 y of age.
Impaired liver, kidney, cardiac, or respiratory function; history of allergies; older adult or debilitated patients; patients with fever; hyperthyroidism; diabetes mellitus or severe anemia; during labor and delivery; patient with borderline hypoadrenal function.
Route & dosage
adult:PO 100–300 mg/d
IV/IM 200–600 mg up to 20 mg/kg
child:PO/IV 3–8 mg/kg or 125 mg/m2/d
neonate:PO/IV 3–4 mg/kg/d (max: 5 mg/kg/d)
adultchild: IV 15–18 mg/kg in single or divided doses (max: 20 mg/kg)
neonate:IV 15–20 mg/kg in single or divided doses
adult:PO 30–120 mg/d
IV/IM 100–200 mg/d
child:PO 6 mg/kg/d or 180 mg/m2 in 3 divided doses
IV/IM 16–100 mg/d (1–3 mg/kg)
- Make sure patient actually swallows pill and does not “cheek” it.
- Give crushed and mixed with a fluid or with food if patient cannot swallow pill. Do not permit patient to swallow dry crushed drug.
- Give IM deep into large muscle mass; do not exceed 5 mL at any one site.
- Note: Verify correct IV concentration and rate of infusion for neonates, infants, children with physician. Use IV route ONLY if other routes are not feasible.
PREPARE direct: Slowly add at least 10 mL of sterile water for injection to ampule. Rotate ampule to dissolve (may take several minutes). If solution not clear in 5 min or if a precipitate remains, discard.
ADMINISTER direct: Give 60 mg or fraction thereof over at least 60 sec. Give within 30 min after preparation.
Incompatibilities Solution / Additive: Benzquinamide, cephalothin, chlorpromazine, codeine phosphate, ephedrine, hydralazine, hydrocortisone sodium succinate, hydroxyzine, insulin, levorphanol, meperidine, methadone, morphine, norepinephrinetetracyclines, procaine, prochlorperazine, promazine, promethazine, ranitidine, streptomycin, vancomycin. Y-site: Amphotericin B cholesteryl complex, hydromorphone, TPN with albumin.
Be aware that extravasation of IV phenobarbital may cause necrotic tissue changes that necessitate skin grafting. Check injection site frequently.
BodyWhole:Myalgia, neuralgia, CNS depression, coma, and death.
CNS:Somnolence, nightmares, insomnia, “hangover,” headache, anxiety, thinking abnormalities, dizziness, nystagmus, irritability, paradoxic excitement and exacerbation of hyperkinetic behavior (in children); confusion or depression or marked excitement (older adult or debilitated patients); ataxia.
CV:Bradycardia, syncope, hypotension.
GI:Nausea, vomiting, constipation, diarrhea, epigastric pain, liver damage.
Hematologic:Megaloblastic anemia, agranulocytosis, thrombocytopenia.
Metabolic:Hypocalcemia, osteomalacia, rickets.
Musculoskeletal:Folic acid deficiency, vitamin D deficiency.
Skin:Mild maculopapular, morbilliform rash; erythema multiforme, Stevens-Johnson syndrome, exfoliative dermatitis (rare).
Assessment & Drug Effects
- Observe patients receiving large doses closely for at least 30 min to ensure that sedation is not excessive.
- Keep patient under constant observation when drug is administered IV, and record vital signs at least every hour or more often if indicated.
- Lab tests: Obtain liver function and hematology tests and determinations of serum folate and vitamin D levels during prolonged therapy.
- Monitor serum drug levels. Serum concentrations >50 mcg/mL may cause coma. Therapeutic serum concentrations of 15–40 mcg/mL produce anticonvulsant activity in most patients. These values are usually attained after 2 or 3 wk of therapy with a dose of 100–200 mg/d.
- Expect barbiturates to produce restlessness when given to patients in pain because these drugs do not have analgesic action.
- Be prepared for paradoxical responses and report promptly in older adult or debilitated patient and children (i.e., irritability, marked excitement [inappropriate tearfulness and aggression in children], depression, and confusion).
- Monitor for drug interactions. Barbiturates increase the metabolism of many drugs, leading to decreased pharmacologic effects of those drugs. Whenever a barbiturate is added to an established regimen of another drug, observe for changes in effectiveness of the first drug at least during early phase of barbiturate use.
- Monitor for and report chronic toxicity symptoms (e.g., ataxia, slurred speech, irritability, poor judgment, slight dysarthria, nystagmus on vertical gaze, confusion, insomnia, somatic complaints).
Patient & Family Education
- Be aware that anticonvulsant therapy may cause drowsiness during first few weeks of treatment, but this usually diminishes with continued use.
- Avoid potentially hazardous activities requiring mental alertness until response to drug is known.
- Do not consume alcohol in any amount when taking a barbiturate; it may severely impair judgment and abilities.
- Increase vitamin D-fortified foods (e.g., milk products) because drug increases vitamin D metabolism. A vitamin D supplement may be prescribed.
- Maintain adequate dietary folate intake: fresh vegetables (especially green leafy), fresh fruits, whole grains, liver. Long-term therapy may result in nutritional folate (B9) deficiency. A supplement of folic acid may be prescribed.
- Adhere to drug regimen (i.e., do not change intervals between doses or increase or decrease doses) without contacting physician.
- Do not stop taking drug abruptly because of danger of withdrawal symptoms (8–12 h after last dose), which can be fatal.
- Report to physician the onset of fever, sore throat or mouth, malaise, easy bruising or bleeding, petechiae, jaundice, rash when on prolonged therapy.
- Avoid pregnancy when receiving barbiturates. Use or add barrier device to hormonal contraceptive when taking prolonged therapy.
- Do not breast feed while taking this drug.