Source: FDA, National Drug Code (US) Revision Year: 2023
Acute intermittent porphyria as well as allergic or idiosyncratic reactions to meprobamate or related compounds such as carisoprodol, mebutamate, tybamate, or carbromal.
Physical dependence, psychological dependence, and abuse have occurred. When chronic intoxication from prolonged use occurs, it usually involves ingestion of greater than recommended doses and is manifested by ataxia, slurred speech, and vertigo.
Therefore, careful supervision of dose and amounts prescribed is advised, as well as avoidance of prolonged administration, especially for alcoholics and other patients with a known propensity for taking excessive quantities of drugs.
Sudden withdrawal of the drug after prolonged and excessive use may precipitate recurrence of pre-existing symptoms such as anxiety, anorexia, insomnia, or withdrawal reactions such as vomiting, ataxia, tremors, muscle twitching, confusional states, hallucinosis, and rarely, convulsive seizures. Such seizures are more likely to occur in persons with central nervous system damage or pre-existent or latent convulsive disorders. Onset of withdrawal symptoms occurs usually within 12 to 48 hours after discontinuation of meprobamate; symptoms usually cease within the next 12 to 48 hours.
When excessive dosage has continued for weeks or months, dosage should be reduced gradually over a period of one or two weeks rather than abruptly stopped. Alternatively, a long-acting barbiturate may be substituted, then gradually withdrawn.
Patients should be warned that meprobamate may impair the mental and/or physical abilities required for performance of potentially hazardous tasks such as driving or operating machinery.
Since the effects of meprobamate and alcohol or meprobamate and other CNS depressants or psychotropic drugs may be additive, appropriate caution should be exercised with patients who take more than one of these agents simultaneously.
An increased risk of congenital malformations associated with the use of minor tranquilizers (meprobamate, chlordiazepoxide and diazepam) during the first trimester of pregnancy has been suggested in several studies. Because use of these drugs is rarely a matter of urgency, their use during this period should almost always be avoided. The possibility that a woman of childbearing potential may be pregnant at the time of institution of therapy should be considered. Patients should be advised that if they become pregnant during therapy or intend to become pregnant they should communicate with their physician about the desirability of discontinuing the drug.
Meprobamate passes the placental barrier. It is present both in umbilical cord blood at or near maternal plasma levels and in breast milk of lactating mothers at concentrations two to four times that of maternal plasma. When use of meprobamate is contemplated in breastfeeding patients, the drug’s higher concentration in breast milk as compared to maternal plasma should be considered.
Meprobamate tablets should not be administered to children under age six, since there is a lack of documented evidence for safety and effectiveness in this age group.
Drowsiness, ataxia, dizziness, slurred speech, headache, vertigo, weakness, paresthesias, impairment of visual accommodation, euphoria, overstimulation, paradoxical excitement, fast EEG activity.
Nausea, vomiting, diarrhea.
Palpitation, tachycardia, various forms of arrhythmia, transient ECG changes, syncope; also hypotensive crisis (including one fatal case).
Allergic or idiosyncratic reactions are usually seen within the period of the first to fourth dose in patients having had no previous contact with the drug. Milder reactions are characterized by an itchy, urticarial, or erythematous maculopapular rash which may be generalized or confined to the groin. Other reactions have included leukopenia, acute nonthrombocytopenic purpura, petechiae, ecchymoses, eosinophilia, peripheral edema, adenopathy, fever, fixed drug eruption with cross reaction to carisoprodol, and cross sensitivity between meprobamate/mebutamate and meprobamate/carbromal.
More severe hypersensitivity reactions, rarely reported, include hyperpyrexia, chills, angioneurotic edema, bronchospasm, oliguria and anuria. Also, anaphylaxis, erythema multiforme, exfoliative dermatitis, stomatitis, proctitis, Stevens-Johnson syndrome and bullous dermatitis, including one fatal case of the latter following administration of meprobamate in combination with prednisolone.
In case of allergic or idiosyncratic reactions to meprobamate, discontinue the drug and initiate appropriate symptomatic therapy, which may include epinephrine, antihistamines, and in severe cases, corticosteroids. In evaluating possible allergic reactions, also consider allergy to excipients.
Agranulocytosis and aplastic anemia have been reported. These cases rarely were fatal. Rare cases of thrombocytopenic purpura have been reported.
Exacerbation of porphyric symptoms.
The lowest effective dose should be administered, particularly to elderly and/or debilitated patients, in order to preclude oversedation.
The possibility of suicide attempts should be considered and the least amount of drug feasible should be dispensed at any one time.
Meprobamate is metabolized in the liver and excreted by the kidney; to avoid its excess accumulation, caution should be exercised in administration to patients with compromised liver or kidney function.
Meprobamate occasionally may precipitate seizures in epileptic patients.
Clinical studies of meprobamate tablets did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.
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