Phenobarbital

Phenobarbital comes as a tablet and an elixir (liquid) to take by mouth. It is usually taken one to three times a day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take phenobarbital exactly as directed.

If you take phenobarbital for a long time, it may not control your symptoms as well as it did at the beginning of your treatment. Talk to your doctor about how you are feeling during your treatment.

Phenobarbital can be habit-forming. Do not take a larger dose, take it more often, or take it for a longer time than prescribed by your doctor.

Do not stop taking phenobarbital without talking to your doctor. If you suddenly stop taking phenobarbital, you may experience withdrawal symptoms such as anxiety, muscle twitching, uncontrollable shaking of a part of the body, weakness, dizziness, changes in vision, nausea, vomiting, seizures, confusion,difficulty falling asleep or staying asleep, or dizziness or fainting when getting up from a lying position. Your doctor will probably decrease your dose gradually.

Before taking phenobarbital,

• tell your doctor and pharmacist if you are allergic to phenobarbital; other barbiturates such as amobarbital (Amytal), butabarbital (Butisol), pentobarbital, and secobarbital (Seconal); any other medications, or any of the ingredients in phenobarbital tablets or liquid. Ask your doctor or pharmacist for a list of the ingredients.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: anticoagulants ('blood thinners') such as warfarin (Coumadin); disulfiram (Antabuse); doxycycline (Vibramycin); griseofulvin (Fulvicin); hormone replacement therapy (HRT); monoamine oxidase (MAO) inhibitors such as isocarboxazid (Marplan), phenelzine (Nardil), seligiline (Eldepryl, Emsam, Zelapar) , or tranylcypromine (Parnate); medications for anxiety, depression, pain, asthma, colds, or allergies; certain medications for seizures such as phenytoin (Dilantin) and valproate (Depakene); oral steroids such as dexamethasone (Decadron, Dexone), methylprednisolone (Medrol), and prednisone (Deltasone);sedatives; sleeping pills; and tranquilizers. Your doctor may need to change the doses of your medications or monitor you more carefully for side effects.
• tell your doctor if you have or have ever had porphyria (condition in which certain natural substances build up in the body and may cause stomach pain, changes in thinking and behavior, and other symptoms); any condition that causes shortness of breath or difficulty breathing; or liver disease. Your doctor will probably tell you not to take phenobarbital.
• tell your doctor if you drink or have ever drunk large amounts of alcohol, used street drugs, or overused prescription medications; if you have pain now or have any condition that causes you ongoing pain; if you have ever thought about harming or killing yourself or planned or tried to do so; and if you have or have ever had depression, any condition that affects your adrenal gland (small gland next to the kidney that produces important natural substances), or kidney disease.
• tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking phenobarbital, call your doctor. Phenobarbital may harm the fetus.
• you should know that phenobarbital may decrease the effectiveness of hormonal contraceptives (birth control pills, patches, rings, injections, implants, or intrauterine devices). Talk to your doctor about methods of birth control that will work for you while you are taking phenobarbital. Tell your doctor if you have a missed period or think you may be pregnant while you are taking phenobarbital.
• if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking phenobarbital.
• you should know that this medication may make you drowsy. Do not drive a car or operate machinery until you know how this medication affects you.
• avoid drinking alcohol during your treatment with phenobarbital. Alcohol can make the side effects of phenobarbital worse.

Phenobarbital is a barbiturate, nonselective central nervous system depressant which is primarily used as a sedative hypnotic and also as an anticonvulsant in subhypnotic doses.

Phenobarbital Tablets and Elixir are administered orally and are contained in DEA Schedule IV. Barbiturates are substituted pyrimidine derivatives in which the basic structure common to these drugs is barbituric acid, a substance which has no central nervous system (CNS) activity. CNS activity is obtained by substituting alkyl, alkenyl, or aryl groups on the pyrimidine ring.

Inactive Ingredients

The following adverse reactions and their incidence were compiled from surveillance of thousands of hospitalized patients.

• Nervous system: Somnolence.

• Nervous system: Agitation, confusion, hyperkinesia, ataxia, CNS depression, nightmares, nervousness, psychiatric disturbance, hallucinations, insomnia, anxiety, dizziness, thinking abnormality.
• Respiratory system: Hypoventilation, apnea.
• Cardiovascular system: Bradycardia, hypotension, syncope.
• Digestive system: Nausea, vomiting, constipation.
• Other reported reactions: Headache, injection site reactions, hypersensitivity reactions (angioedema skin rashes, exfoliative dermatitis), fever, liver damage, megaloblastic anemia following chronic phenobarbital use.

DRUG ABUSE AND DEPENDENCE

Symptoms of acute intoxication with phenobarbital include unsteady gait, slurred speech, and sustained nystagmus. Mental signs of chronic intoxication include confusion, poor judgment, irritability, insomnia, and somatic complaints.

Symptoms of phenobarbital dependence are similar to those of chronic alcoholism. If an individual appears to be intoxicated with alcohol to a degree that is radically disproportionate to the amount of alcohol in his or her blood, the use of barbiturates should be suspected. The lethal dose of a barbiturate is far less if alcohol is also ingested. The symptoms of phenobarbital withdrawal can be severe and may cause death. Minor withdrawal symptoms may appear 8 to 12 hours after the last dose of phenobarbital. These symptoms usually appear in the following order: anxiety, muscle twitching, tremor of hands and fingers, progressive weakness, dizziness, distortion in visual perception, nausea, vomiting, insomnia, and orthostatic hypotension. Major withdrawal symptoms (convulsions and delirium) may occur within 16 hours and last up to 5 days after abrupt cessation of this drug. Intensity of withdrawal symptoms gradually declines over a period of approximately 15 days. Individuals susceptible to phenobarbital abuse and dependence include alcoholics and opiate abusers, as well as other sedative- hypnotic and amphetamine abusers.

Drug dependence on phenobarbital arises from repeated administration of the barbiturate or an agent with barbiturate- like effect on a continuous basis, generally in amounts exceeding therapeutic dose levels. The characteristics of drug dependence on phenobarbital include: (a) a strong desire or need to continue taking the drug, (b) a tendency to increase the dose, (c) a psychic dependence on the effects of the drug related to subjective and individual appreciation of those effects, and (d) a physical dependence on the effects of the drug requiring its presence for maintenance of homeostasis and resulting in a definite, characteristic, and self-limited abstinence syndrome when the drug is withdrawn.

Treatment of phenobarbital dependence consists of cautious and gradual withdrawal of the drug. One method involves substituting a 30 mg dose of phenobarbital for each 100 to 200 mg dose that the patient has been taking. The total daily amount of phenobarbital is then administered in 3 to 4 divided doses, not to exceed 600 mg daily. Should signs of withdrawal occur on the first day of treatment, a loading dose of 100 to 200 mg of phenobarbital may be administered IM in addition to the oral dose. After stabilization on phenobarbital, the total daily dose is decreased by 30 mg a day as long as withdrawal is proceeding smoothly. A modification of this regimen involves initiating treatment at the patient's regular dosage level and decreasing the daily dosage by 10 percent if tolerated by the patient.

Infants physically dependent on phenobarbital may be given a lower dose of phenobarbital at 3 to 10 mg/kg/day. After withdrawal symptoms (hyperactivity, disturbed sleep, tremors, hyperreflexia) are relieved, the dosage of phenobarbital should be gradually decreased and completely withdrawn over a 2-week period.

Phenobarbital is in a group of drugs called barbiturates (bar-BIT-chur-ates). Phenobarbital slows the activity of your brain and nervous system.

Phenobarbital is used to treat or prevent seizures. It is also used short-term to treat insomnia, or as a sedative before surgery.

Phenobarbital may also be used for purposes not listed in this medication guide.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phenobarbital can be fatal.

Overdose symptoms may include slow or shallow breathing, weak pulse, cold or clammy skin, little or no urination, pinpoint pupils, feeling cold, or fainting.

Phenobarbital is contraindicated in patients who are hypersensitive to barbiturates. In such patients, severe hepatic damage can occur from ordinary doses and is usually associated with dermatitis and involvement of parenchymatous organs. A personal or familial history of acute intermittent porphyria represents one of the few absolute contraindications to the use of barbiturates. Phenobarbital is also contraindicated in patients with marked impairment of liver function, or respiratory disease in which dyspnea or obstruction is evident. It should not be administered to persons with known previous addiction to the sedative/hypnotic group, since ordinary doses may be ineffectual and may contribute to further addiction.

The signs and symptoms of barbiturate poisoning are referable especially to the central nervous system and the cardiovascular system. Moderate intoxication resembles alcoholic inebriation. In severe intoxication, the patient is comatose, the level of reflex activity conforming in a general way to the intensity of the central depression. The deep reflexes may persist for some time despite coexistent coma. The Babinski sign is often positive. The EEG may be of the “burst-suppression” type, with brief periods of electrical silence. The pupils may be constricted and react to light, but late in the course of barbiturate poisoning they may show hypoxic paralytic dilatation. Respiration is affected early. Breathing may be either slow or rapid and shallow; Cheyne-Stokes rhythm may be present. Respiratory minute volume is diminished, and hypoxia and respiratory acidosis may develop. The blood pressure falls, owing partly to depression of medullary vasomotor centers; partly to a direct action of the drug on the myocardium, sympathetic ganglia, and vascular smooth muscle; partly to hypoxia.

The patient thus develops a typical shock syndrome, with a weak and rapid pulse, cold and clammy skin, and a rise in the hematocrit. Respiratory complications (atelectasis, pulmonary edema, and bronchopneumonia) and renal failure are much dreaded and not infrequent concomitant of severe barbiturate poisoning. There is usually hypothermia, sometimes with temperatures as low as 32°C.

Treatment:

General management should consist of symptomatic and supportive therapy, including gastric lavage, administration of intravenous fluids, and maintenance of blood pressure, body temperature and adequate respiratory exchange. Dialysis will increase the rate of removal of barbiturates from the body fluids. Antibiotics may be required to control pulmonary complications.

• Anticonvulsant, Barbiturate
• Barbiturate

Oral: 10 to 12 hours; IV: >6 hours

Half-Life Elimination

Neonates (<48 hours old), Infants, and Children: ~110 hours (60 to 180 hours); Adults: ~79 hours (range: 53 to 118 hours)

Protein Binding

Neonates: 36% to 43% (Patsalos 2008)

Adults: 50% to 60% (Patsalos 2008)

Sedation: Use as a sedative

Seizures: Management of generalized tonic-clonic, status epilepticus, and partial seizures

Note: Use to treat insomnia is not recommended (Schutte-Rodin 2008)

Oral: Store between 20°C and 25°C (68°F and 77°F). Protect from light.

Injection: Store between 20°C and 25°C (68°F and 77°F); excursions are permitted to 15°C to 30°C (59°F to 86°F).

Frequency not defined.

Cardiovascular: Bradycardia, hypotension, syncope, thrombophlebitis (IV)

Central nervous system: Agitation, anxiety, ataxia, central nervous system stimulation, central nervous system depression, confusion, dizziness, drowsiness, hallucination, hangover effect, headache, impaired judgement, insomnia, lethargy, nervousness, nightmares

Dermatologic: Exfoliative dermatitis, skin rash, Stevens-Johnson syndrome

Gastrointestinal: Constipation, nausea, vomiting

Genitourinary: Oliguria

Hematologic & oncologic: Agranulocytosis, thrombocytopenia, megaloblastic anemia

Local: Pain at injection site

Neuromuscular & skeletal: Hyperkinesia, laryngospasm

Respiratory: Apnea (especially with rapid IV use), hypoventilation, respiratory depression

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience fatigue, headache, nausea, vomiting, or injection site irritation. Have patient report immediately to prescriber shortness of breath, difficulty breathing, slow breathing, shallow breathing, severe dizziness, passing out, bradycardia, change in balance, confusion, severe anxiety, severe loss of strength and energy, bone pain, insomnia, seizures, or signs of Stevens-Johnson syndrome/toxic epidermal necrolysis (red, swollen, blistered, or peeling skin [with or without fever]; red or irritated eyes; or sores in mouth, throat, nose, or eyes) (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.