Barbiturates

Barbiturates

Definition

Barbiturates are a large class of drugs, consisting of many different brand name products with generic equivalents, that are used primarily for mild sedation, general anesthesia, and as a treatment for some types of epilepsy. One barbiturate, butalbital, exists only as a component of several headache preparations. The most common members of the barbiturate family are phenobarbital (Luminal)), pentobarbital (Nembutal), amobarbital (Amytal), secobarbital (Seconal), thiopental (Pentothal), methohexital (Brevital), and butalbital (component of Fiorinal and Fioricet). They exist in numerous formulations and strengths.

Purpose

Barbiturates are used to sedate patients prior to surgery as well as to produce general anesthesia, to treat some forms of epilepsy, and to treat simple and migraine headache. These drugs are highly addictive and are often abused as recreational drugs. Although still commercially available, barbiturates such as secobarbital, pentobarbital, and amobarbital are no longer routinely recommended for the treatment of insomnia because of their ability to cause dependence, tolerance, and withdrawal. These drugs also have significant side effects when taken in large doses and can cause respiratory failure and death.

Description

The therapeutic effects of barbiturates as a class of drugs are all related to their ability to sedate and, at high enough doses and with certain preparations, to induce sleep. All barbiturates also have anticonvulsant properties although phenobarbital is the preferred barbiturate to treat epilepsy because it can produce anticonvulsant effects at levels low enough not to cause extreme sedation or sleep.

Recommended dosage

The typical dose of phenobarbital for use as an anticonvulsant in adults is 50–100 mg given two to three times per day. When a series of serious seizures known as status epilepticus occurs, adults are usually first given 300–800 mg intravenously (directly into the vein) followed by 120–240 mg every 20 minutes up to a maximum of 1000–2000 mg. For sedation, adults are given 30–120 mg per day divided into two or three doses. For sedation before surgery, 100–200 mg are given in an intramuscular injection (a shot) about one hour before the surgery.

The typical dose for an anticonvulsant effect in newborns is 2 mg to 4 mg of phenobarbital per kilogram of body weight per day. In infants, this dose is 5 mg to 8 mg per kilogram of body weight per day. In children one to five years of age, the dose is 6 mg to 8 mg per kilogram of body weight per day. In children aged five to 12 years, the dose is 4 mg to 6 mg per kilogram of body weight per day. All of these doses are given in one to two divided doses per day.

In newborns with status epilepticus, phenobarbital 15 mg to 20 mg per kilogram of body weight is given in a single or divided dose. Infants and children are given 10 mg to 20 mg per kilogram of body weight in a single or divided dose. They may also receive 5 mg per kilogram of body weight every 15 to 30 minutes up to a maximum of 40 mg per kilogram body weight. For anesthesia before surgery, 1 mg to 3 mg per kilogram of body weight is given about one hour before the surgery.

The typical dose of butalbital, as a component of headache preparations such as Fiorinal or Fioricet, is 50-100 mg administered every four to six hours as needed.

Precautions

Children who are hyperactive should not receive phenobarbital or other barbiturates. Some children paradoxically become stimulated and hyperactive after receiving barbiturates.

The use of barbiturates in the elderly (over age 65) should be watched closely. Elderly patients must be carefully monitored for confusion, agitation, delirium , and excitement if they take barbiturates. Barbiturates should be avoided in elderly patients who are receiving drugs for other mental disorders such as schizophrenia or depression.

Women should not use barbiturates during pregnancy unless they are necessary to control seizures. In these cases, they should take the minimum amount to control the seizures. Barbiturate use by pregnant women has been associated with increased risk of fetal damage and bleeding during childbirth. Women who are breast-feeding should not take barbiturates because these drugs enter the breast milk and may cause serious side effects in the nursing baby.

Long-term barbiturate use should be avoided unless there is a strong medical need, as in the case of epilepsy, because of the potential for addiction , dependence, tolerance, and withdrawal. People should not drive, operate heavy equipment, or perform other hazardous activities requiring mental alertness while taking barbiturates.

Side effects

The most common side effect of barbiturate use is drowsiness. Less common side effects include agitation, confusion, breathing difficulties, abnormally low blood pressure, nausea, vomiting, constipation, lower body temperature, decreased heart rate, movement difficulty, nightmares, anxiety, nervousness, mental depression, and dizziness. Rare but reported side effects include fever, headache, anemia, allergic reactions, and liver damage.

Interactions

Patients should always tell their doctor and dentist when they are taking barbiturates. Barbiturates should generally not be taken with other drugs used to treat mental disorders.

There are a number of drugs that barbiturates should not be combined with because the barbiturates may increase the metabolism of these drugs and thus, reduce the amount of these drugs available to be of benefit. These drugs include oral corticosteroids such as predisolone, methylprednisolone, prednisone, or dexamethasone, estrogen and oral contraceptives, blood-thinning medications such as warfarin (Coumadin), the antibiotic doxycycline (Vibramycin), and anticonvulsants such as phenytoin (Dilantin).

Barbiturates should not be combined with alcohol because the combination produces additive depressant effects in the central nervous system.

Barbiturates may lower the amount of absorption of the vitamins D and K.

Resources

BOOKS

Consumer Reports Staff. Consumer Reports Complete Drug Reference. 2002 ed. Denver: Micromedex Thomson Healthcare, 2001.

Ellsworth, Allan J., and others. Mosby's Medical Drug Reference, 2001–2002. St. Louis: Mosby, 2001.

Hardman, Joel G. and Lee E. Limbird, eds. Goodman & Gilman's The Pharmacological Basis of Therapeutics. 10th ed. New York: McGraw-Hill, 2001.

Mosby's GenRx Staff. Mosby's GenRx. 9th ed. St. Louis: Mosby, 1999.

Venes, Donald, and Clayton L. Thomas. Taber's Cyclopedic Medical Dictionary. 19th ed. Philadelphia: F. A. Davis, 2001.

Mark Mitchell, M.D.