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1. Habit forming: Phenobarbital may be habit forming. Tolerance, psychological and physical dependence may occur with continued use. (See ADVERSE REACTIONS: Drug Abuse and Dependence). 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. Phenobarbital should be withdrawn gradually. (See ADVERSE REACTIONS: Drug Abuse and Dependence.)
2. Acute or chronic pain: Caution should be exercised when Phenobarbital is administered to patients with acute or chronic pain, because paradoxical excitement could be induced or important symptoms could be masked. However, the use of phenobarbital as a sedative in the postoperative surgical period and as an adjunct to cancer chemotherapy is well established.
3. Use in pregnancy: Phenobarbital can cause fetal damage when administered to a pregnant woman. Retrospective case-controlled studies have suggested a connection between the maternal consumption of phenobarbital and higher than expected incidence of fetal abnormalities. Following oral administration, Phenobarbital readily crosses the placental barrier and is distributed throughout fetal tissues with highest concentrations found in the placenta, fetal liver, and brain.
Withdrawal symptoms occur in infants born to mothers who receive phenobarbital throughout the last trimester of pregnancy. (See ADVERSE REACTIONS: 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.
Phenobarbital may be habit forming. Tolerance and psychological and physical dependence may occur with continuing use. (See ADVERSE REACTIONS: Drug Abuse and Dependence.) Phenobarbital 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 Phenobarbital with marked excitement, depression, and confusion. In some persons, phenobarbital repeatedly produces excitement rather than depression.
In patients with hepatic damage, phenobarbital should be administered with caution and initially reduced doses. Phenobarbital should not be administered to patients showing the premonitory signs of hepatic coma.
Prolonged therapy with phenobarbital should be accompanied by periodic laboratory evaluation of organ systems, including hematopoietic, renal, and hepatic systems (See General - above and ADVERSE REACTIONS.)
Human-data: 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.
Nonteratogenic effects: Reports of infants suffering from long- term phenobarbital exposure in utero included the acute withdrawal syndrome of seizures and hyperirritability from birth to a delayed onset of up to 14 days. (See ADVERSE REACTIONS: Drug Abuse and Dependence.)
Labor and Delivery
Hypnotic doses of phenobarbital do not appear to significantly impair uterine activity during labor. Full anesthetic doses of phenobarbital decrease the force and frequency of uterine contractions. Administration of sedative-hypnotic phenobarbital to the mother during labor may result in respiratory depression in the newborn. Premature infants are particularly susceptible to the depressant effects of phenobarbital. If phenobarbital is used during labor and delivery, resuscitation equipment should be available.
Data are currently not available to evaluate the effect of phenobarbital on the later growth, development, and functional maturation of the child.
Caution should be exercised when phenobarbital is administered to a nursing woman since small amounts of phenobarbital are excreted in the milk.
Last reviewed on RxList: 12/8/2004
This monograph has been modified to include the generic and brand name in many instances.
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