Phenobarbital

Sedative Anticonvulsant- For the treatment of generalized and partial seizures.

• The dose of phenobarbital must be individualized with full knowledge of its particular characteristics
• Factors of consideration are the patient's age, weight, and condition
• ADVERSE REACTIONS The following adverse reactions have been reported: CNS Depression- Residual sedation or "hangover," drowsiness, lethargy, and vertigo
• Emotional disturbances and phobias may be accentuated
• In some persons, barbiturates such as phenobarbital repeatedly produce excitement rather than depression, and the patient may appear to be inebriated
• Irritability and hyperactivity can occur in children
• Like other nonanalgesic hypnotic drugs, barbiturates such as phenobarbital, when given in the presence of pain, may cause restlessness, excitement, and even delirium
• Rarely, the use of barbiturates results in localized or diffuse myalgic, neuralgic, or arthritic pain, especially in psychoneurotic patients with insomnia
• The pain may appear in paroxysms, is most intense in the early morning hours, and is most frequently located in the region of the neck, shoulder girdle, and upper limbs
• Symptoms may last for days after the drug is discontinued
• Respiratory/Circulatory- Respiratory depression, apnea, circulatory collapse
• Allergic- Acquired hypersensitivity to barbiturates consists chiefly in allergic reactions that occur especially in persons who tend to have asthma, urticaria, angioedema, and similar conditions
• Hypersensitivity reactions in this category include localized swelling, particularly of the eyelids, cheeks, or lips, and erythematous dermatitis. …

4. Usage in Children Phenobarbital has been reported to be associated with cognitive deficits in children taking it for complicated febrile seizures.

• The following information and instructions should be given to patients receiving barbiturates
• The use of barbiturates carries with it an associated risk of psychological and/or physical dependence
• The patient should be warned against increasing the dose of the drug without consulting a physician
• Barbiturates may impair the mental and/or physical abilities required for the performance of potentially hazardous tasks, such as driving a car or operating machinery
• The patient should be cautioned accordingly
• Alcohol should not be consumed while taking barbiturates. …

Phenobarbital is contraindicated in patients who are hypersensitive to barbiturates, in patients with a history of manifest or latent porphyria, and in patients with marked impairment of liver function or respiratory disease in which dyspnea or obstruction is evident.

Most reports of clinically significant drug interactions occurring with the barbiturates have involved phenobarbital. However, the application of these data to other barbiturates appears valid and warrants serial blood level determinations of the relevant drugs when there are multiple therapies. 1. Anticoagulants Phenobarbital lowers the plasma levels of dicumarol and causes a decrease in anticoagulant activity as measured by the prothrombin time. Barbiturates can induce hepatic microsomal enzymes resulting in increased metabolism and decreased anticoagulant response of oral anticoagulants (eg, warfarin, acenocoumarol, dicumarol, and phenprocoumon). …

1. Habit-Forming Phenobarbital may be habit-forming. Tolerance and psychological and physical dependence may occur with continued use ( see Drug Abuse and Dependence and Pharmacokinetics under Clinical Pharmacology ). Patients who have psychologic 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. In order 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. …

The following adverse reactions have been reported: CNS Depression- Residual sedation or "hangover," drowsiness, lethargy, and vertigo. Emotional disturbances and phobias may be accentuated. In some persons, barbiturates such as phenobarbital repeatedly produce excitement rather than depression, and the patient may appear to be inebriated. Irritability and hyperactivity can occur in children. Like other nonanalgesic hypnotic drugs, barbiturates such as phenobarbital, when given in the presence of pain, may cause restlessness, excitement, and even delirium. …

3. Usage 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. Barbiturates readily cross the placental barrier and are distributed throughout fetal tissues; the highest concentrations are found in the placenta, fetal liver and brain. …

Signs and Symptoms The onset of symptoms following a toxic oral exposure to phenobarbital may not occur until several hours following ingestion. The toxic dose of barbiturates varies considerably. In general, an oral dose of 1 g of most barbiturates produces serious poisoning in an adult. Death commonly occurs after 2 to 10 g of ingested barbiturate. The sedated, therapeutic blood levels of phenobarbital range between 5 to 40 µg/mL; the usual lethal blood level ranges from 100 to 200 µg/mL. …

Controlled Substance Phenobarbital is a Schedule IV drug. Dependence Barbiturates may be habit-forming. Tolerance, psychological dependence, and physical dependence may occur especially following prolonged use of high doses of barbiturates. Daily administration in excess of 400 mg of pentobarbital or secobarbital for approximately 90 days is likely to produce some degree of physical dependence. A dosage of 600 to 800 mg taken for at least 35 days is sufficient to produce withdrawal seizures. …

STORAGE Keep tightly closed. Store at controlled room temperature, 20°-25°C (68° -77°F). [See USP]

Take it when you remember, unless it is nearly time for the next dose. Then skip the missed one. Never take two doses at once to make up for it. Check your leaflet, as some medicines are different.