Meprobamate—marketed as Miltown is a carbamate derivative used as an anxiolytic drug.
Largely been replaced by the benzodiazepines due to their wider therapeutic index and lower incidence of serious side effects.
Pregnancy category AU: C
Routes of administration Oral
US: Schedule IV
Metabolism Hepatic
Elimination half-life 10 hours
Excretion Renal
Meprobamate has most of the pharmacological effects and dangers of barbiturates and acts at the barbiturate binding site, though it is less sedating at effective doses.
It is reported to have some anticonvulsant properties against absence seizures, but can exacerbate generalized tonic-clonic seizures.
Its mechanism of action is not completely known. It has been shown in animal studies to have effects at multiple sites in the central nervous system, including the thalamus and limbic system.
Meprobamate binds to GABAA receptors which interrupts neuronal communication in the reticular formation and spinal cord, causing sedation and altered perception of pain.
Meprobamate is exceptionally dangerous when used in combination with other GABA-mediated drugs, including alcohol.
It is also a potent adenosine reuptake inhibitor.
Related drugs include carisoprodol and tybamate (prodrugs of meprobamate), phenprobamate, felbamate, mebutamate, and methocarbamol.
Indications: short-term relief of anxiety, although whether the purported antianxiety effects of meprobamate are separable from its sedative effects is not known.
Its effectiveness as a selective agent for the treatment of anxiety has not been proven in humans, and is not used as often as the benzodiazepines for this purpose.
Meprobamate is available in 200- and 400-mg tablets for oral administration. It is also a component of the combination drug Equagesic, acting as a muscle relaxant.
Meprobamate, like barbiturates, possesses an analgesic/anesthetic potential.
It is also found as a component of the combination analgesic capsules along with paracetamol (acetaminophen), caffeine and codeine phosphate.
Symptoms of meprobamate overdose include drowsiness, headache, sluggishness, unresponsiveness, coma, loss of muscle control, impairment or cessation of breathing; or shock.
Death has been reported with ingestion of as little as 12 g of meprobamate and survival with as much as 40 g.
In an overdose, meprobamate tablets may form a gastric bezoar, requiring physical removal of the undissolved mass,
With protracted use, it can cause physical dependence and a potentially life-threatening abstinence syndrome similar to that of barbiturates and alcohol.