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Barbiturates may be habit forming. Tolerance, psychological, and physical dependence may occur with continued use. (See Drug abuse and Dependence and CLINICAL PHARMACOLOGY.) Patients who have psychological dependence on barbiturates may increase the dosage or decrease the dosage interval without consulting a physician and may subsequently develop a physical dependence on barbiturates. To minimize the possibility of overdosage or the development of dependence, the prescribing and dispensing of sedative-hypnotic barbiturates should be limited to the amount required for the interval until the next appointment. Abrupt cessation after prolonged use in the dependent person may result in withdrawal symptoms, including delirium, convulsions, and possibly death. Barbiturates should be withdrawn gradually from any patient known to be taking excessive dosage over long periods of time. (See Drug abuse and Dependence.)
Acute or Chronic Pain
Caution should be exercised when barbiturates are administered to patients with acute or chronic pain, because paradoxical excitement could be induced or important symptoms could be masked. However, the use of barbiturates as sedatives in the postoperative surgical period and as adjuncts to cancer chemotherapy is well established.
Use in Pregnancy
Barbiturates can cause fetal damage when administered to a pregnant woman. Retrospective, case-controlled studies have suggested a connection between the maternal consumption of barbiturates and a higher than expected incidence of fetal abnormalities. Following oral or parenteral administration, barbiturates readily cross the placental barrier and are distributed throughout fetal tissues with highest concentrations found in the placenta, fetal liver, and brain. Fetal blood levels approach maternal blood levels following parenteral administration.
Withdrawal symptoms occur in infants born to mothers who receive barbiturates throughout the last trimester of pregnancy. (See Drug abuse and Dependence.) If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus.
The concomitant use of alcohol or other CNS depressants may produce additive CNS depressant effects.
Barbiturates may be habit forming. Tolerance and psychological and physical dependence may occur with continuing use. (See Drug abuse and Dependence.) Barbiturates should be administered with caution, if at all, to patients who are mentally depressed, have suicidal tendencies, or a history of drug abuse.
Elderly or debilitated patients may react to barbiturates with marked excitement, depression, and confusion. In some persons, barbiturates repeatedly produce excitement rather than depression.
In patients with hepatic damage, barbiturates should be administered with caution and initially in reduced doses. Barbiturates should not be administered to patients showing the premonitory signs of hepatic coma.
Caution and careful adjustment of dosage are required when MEBARAL (mephobarbital) is used in patients with impaired renal, cardiac or respiratory function, and in patients with myasthenia gravis and myxedema. The least quantity feasible should be prescribed or dispensed at any one time in order to minimize the possibility of acute or chronic overdosage.
Vitamin D Deficiency: MEBARAL (mephobarbital) may increase vitamin D requirements, possibly by increasing vitamin D metabolism via enzyme induction. Rarely, rickets and osteomalacia have been reported following prolonged use of barbiturates.
Vitamin K: Bleeding in the early neonatal period due to coagulation defects may follow exposure to anticonvulsant drugs in utero; therefore, vitamin K should be given to the mother before delivery or to the child at birth.
Prolonged therapy with barbiturates should be accompanied by periodic laboratory evaluation of organ systems, including hematopoietic, renal, and hepatic systems. (See PRECAUTIONS [General] and ADVERSE REACTIONS.)
Phenobarbital sodium is carcinogenic in mice and rats after lifetime administration. In mice, it produced benign and malignant liver cell tumors. In rats, benign liver cell tumors were observed very late in life. Phenobarbital is the major metabolite of MEBARAL (mephobarbital) .
In a 29-year epidemiological study of 9,136 patients who were treated on an anticonvulsant protocol which included phenobarbital, results indicated a higher than normal incidence of hepatic carcinoma. Previously, some of these patients were treated with thorotrast, a drug which is known to produce hepatic carcinomas. Thus, this study did not provide sufficient evidence that Phenobarbital sodium is carcinogenic in humans. Phenobarbital is the major metabolite of MEBARAL (mephobarbital) .
A retrospective study of 84 children with brain tumors matched to 73 normal controls and 78 cancer controls (malignant disease other than brain tumors) suggested an association between exposure to barbiturates prenatally and an increased incidence of brain tumors.
Pregnancy Category D-See WARNINGS-Use in Pregnancy.
Reports of infants suffering from long-term barbiturate exposure in utero included the acute withdrawal syndrome of seizures and hyperirritability from birth to a delayed onset of up to 14 days. (See Drug abuse and Dependence.)
Labor and Delivery
Hypnotic doses of these barbiturates do not appear to significantly impair uterine activity during labor. Full anesthetic doses of barbiturates decrease the force and frequency of uterine contractions. Administration of sedative-hypnotic barbiturates to the mother during labor may result in respiratory depression in the newborn. Premature infants are particularly susceptible to the depressant effects of barbiturates. If barbiturates are used during labor and delivery, resuscitation equipment should be available.
Data are currently not available to evaluate the effect of these barbiturates when forceps delivery or other intervention is necessary. Also, data are not available to determine the effect of these barbiturates on the later growth, development, and functional maturation of the child.
Caution should be exercised when a barbiturate is administered to a nursing woman since small amounts of barbiturates are excreted in the milk.
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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