Amobarbital (Amytal) is one of the many different members of the Barbitu-Rate family of central nervous system depressants used to produce relaxation, sleep, anesthesia, and anticonvulsant effects. In terms of the duration of its effects, it is considered an intermediate-acting barbiturate. When taken by mouth, its sedating effects take about 1 hour to develop and last about 6 to 8 hours, although it takes considerably longer for all the drug to leave the body.
In addition to its use as a sedative, amobarbital is occasionally used in psychiatric evaluation in so-called "Amytal interviews," to relax patients in order to help them recall memories or information that has been repressed due to trauma. This technique was sometimes called narcoanalysis or narcotherapy.
DOSAGE AND ADMINISTRATION
Amobarbital may be given orally, intramuscularly, or intravenously for the treatment of insomnia or anxiety. The adult dosage for sedation is 15 to 50 milligrams but 65 to 200 milligrams for sleep. For treating convulsions, the adult dose is 65 to 200 milligrams, with a maximum dose of 500 milligrams.
Amobarbital should not be given to patients with a history of addiction; personal or family history of porphyria; severe kidney, liver, or lung disease; or hypersensitivity to barbiturates.
Amobarbital is incompatible with a number of medications, including dimenhydrinate, phenytoin, hydrocortisone, insulin, morphine, cimetidine, pancuronium, streptomycin, tetracycline, vancomycin, and penicillin G. It may decrease the effectiveness of birth control pills containing estrogen. It has also been shown to increase the risk of birth defects if taken during pregnancy.
The use of amobarbital in "Amytal interviews" has declined since the mid-1990s because of its relatively low success rate. One medical text published in the mid-1990s noted that the amount of clinically useful information obtained by this method is quite limited. Amobarbital interviews appear to be useful primarily in distinguishing between psychosis and delirium. Psychotic patients usually improve with amobarbital, whereas delirious patients get worse.
DEPENDENCY AND ABUSE
Amobarbital has been largely replaced by benzodiazepine medications as a sedative because of the high risk of abuse. It has been dropped from the 1999 edition of the Physicians' Desk Reference, which implies that it is no longer manufactured in the United States. As of 2000, it is still available in Canada. Although amobarbital has been less popular with addicted patients than the more rapidly acting barbiturates (secobarbital and pentobarbital), it is still sold on the street as "blues" or "rainbows" (combinations of amobarbital and secobarbital). A daily dose of 500 to 600 milligrams is considered sufficient to produce dependence. The time necessary to produce dependence is estimated at 30 days. It has often been noted that the symptoms of barbiturate dependence resemble those of chronic alcoholism, though barbiturate withdrawl is more often associated with life-threatening complications than alcohol withdrawl.
Although the toxic dose of amobarbital varies according to height, weight, and other factors, 1 gram taken by mouth usually produces serious poisoning in an adult. Two to 10 grams are usually a fatal dose. Emergency treatment is supportive, including oxygen administration if necessary, fluid therapy and other standard treatment for shock, and forced diuresis if the patient has normal kidney function. This procedure speeds the excretion of the barbiturate in the urine.
The symptoms of withdrawal from amobarbital or any barbiturate may be severe or even fatal if the patient has been taking the drug in large doses (800 mg/day). The barbiturate withdrawal syndrome is similar to delirium tremens. Within 12 to 20 hours after withdrawal, the patient becomes restless and weak. During the second and third days, 75 percent of patients develop convulsions, which may progress to status epilepticus and death. From the third to the fifth day, untreated withdrawal syndrome is marked by delirium, hallucinations, insomnia, fever, and dehydration. To prevent withdrawal syndrome, patients are treated with a dose of phenobarbital equivalent to one-third of the daily dose of amobarbital on which they are dependent. This initial dose of phenobarbital is decreased by 30 milligrams per day until the patient's system is clear of drugs.
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Scott E. Lukas
Revised by Rebecca J. Frey