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 Phenobarbital should be withdrawn gradually.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.
4. Synergistic effects: The concomitant use of alcohol or other
CNS depressants may produce additive CNS depressant effects.
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