"Sleep disorder drugs (hypnotic and sedative drugs) overview
Insomnia, a disorder in which there is difficulty sleeping, occurs occasionally in most people but usually lasts only a few days. The body then "corrects" itself "...
Barbiturates are capable of producing all levels of CNS mood alteration from excitation to mild sedation, to hypnosis, and deep coma. Overdosage can produce death. In high enough therapeutic doses, barbiturates induce anesthesia.
Barbiturates are respiratory depressants. The degree of respiratory depression is dependent upon dose. With hypnotic doses, respiratory depression produced by barbiturates is similar to that which occurs during physiologic sleep with slight decrease in blood pressure and heart rate.
Studies in laboratory animals have shown that barbiturates cause reduction in the tone and contractility of the uterus, ureters, and urinary bladder. However, concentrations of the drugs required to produce this effect in humans are not reached with sedative-hypnotic doses.
Barbiturates do not impair normal hepatic function, but have been shown to induce liver microsomal enzymes, thus increasing and/or altering the metabolism of barbiturates and other drugs. (See PRECAUTIONS - DRUG INTERACTIONS.)
MEBARAL (mephobarbital) exerts a strong sedative and anticonvulsant action but has a relatively mild hypnotic effect. It reduces the incidence of epileptic seizures in grand mal and petit mal. MEBARAL (mephobarbital) usually causes little or no drowsiness or lassitude. Hence, when it is used as a sedative or anticonvulsant, patients usually become more calm, more cheerful, and better adjusted to their surroundings without clouding of mental faculties. MEBARAL (mephobarbital) is reported to produce less sedation than does phenobarbital.
Barbiturates are weak acids that are absorbed and rapidly distributed to all tissues and fluids with high concentrations in the brain, liver, and kidneys. Lipid solubility of the barbiturates is the dominant factor in their distribution within the body. Barbiturates are bound to plasma and tissue proteins to a varying degree with the degree of binding increasing directly as a function of lipid solubility.
Approximately 50% of an oral dose of mephobarbital is absorbed from the gastrointestinal tract. Therapeutic plasma concentrations for mephobarbital have not been established nor has the half-life been determined. Following oral administration, the onset of action of the drug is 30 to 60 minutes and the duration of action is 10 to 16 hours. The primary route of mephobarbital metabolism is N-demethylation by the microsomal enzymes of the liver to form phenobarbital. Phenobarbital may be excreted in the urine unchanged or further metabolized to p-hydroxyphenobarbital and excreted in the urine as glucuronide or sulfate conjugates. About 75% of a single oral dose of mephobarbital is converted to phenobarbital in 24 hours.
Therefore, chronic administration of mephobarbital may lead to an accumulation of phenobarbital (not mephobarbital) in plasma. It has not been determined whether mephobarbital or phenobarbital is the active agent during long-time mephobarbital therapy.
Last reviewed on RxList: 11/17/2008
This monograph has been modified to include the generic and brand name in many instances.
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