The barbiturates are nonselective central nervous system (CNS) depressants primarily used as sedative-hypnotics. In subhypnotic doses, they are also used as anticonvulsants. The barbiturates and their sodium salts are subject to control under the Federal Controlled Substances Act.

Phenobarbital is a barbituric acid derivative for oral administration and occurs as a white, odorless, slightly bitter powder that is soluble in chloroform, freely soluble in alcohol or ether, and slightly soluble in water. Its saturated solution has a pH of about 5.6. Chemically, it is 5-ethyl-5-phenylbarbituric acid with the molecular formula C 12H 12N 2O 3(232.24).

The structural formula is as follows:

Each Phenobarbital Tablet, USP contains 15 mg, 16.2 mg, 30 mg, 32.4 mg, 60 mg, 64.8 mg, 97.2 mg, or 100 mg of phenobarbital, USP.

Inactive ingredients are as follows:

Microcrystalline Cellulose; Lactose Monohydrate; Sodium Starch Glycolate, Type-A; Colloidal Silicon Dioxide; Magnesium Stearate

Phenobarbital, a long-acting barbiturate, is a central nervous system depressant. In ordinary doses, the drug acts as a sedative and anticonvulsant. Its onset of action occurs within 30 minutes, and the duration of action ranges from 5 to 6 hours. It is detoxified in the liver.

Phenobarbital Tablets, USP are indicated for use as a sedative or anticonvulsant.

Phenobarbital is contraindicated in patients who are hypersensitive to barbiturates. In such patients, severe hepatic damage can occur from ordinary doses and is usually associated with dermatitis and involvement of parenchymatous organs. A personal or familial history of acute intermittent porphyria represents one of the few absolute contraindications to the use of barbiturates. Phenobarbital is also contraindicated in patients with marked impairment of liver function, or respiratory disease in which dyspnea or obstruction is evident. It should not be administered to persons with known previous addiction to the sedative/hypnotic group, since ordinary doses may be ineffectual and may contribute to further addiction.

In small doses, the barbiturates may increase the reaction to painful stimuli. Taken by themselves, the barbiturates cannot be relied upon to relieve pain or even to produce sedation or sleep in the presence of severe pain.

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. 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 diffused 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. Rarely, exfoliative dermatitis (e.g., Stevens-Johnson syndrome and toxic epidermal necrolysis) may be caused by phenobarbital and can prove fatal. The skin eruption may be associated with fever, delirium, and marked degenerative changes in the liver and other parenchymatous organs. In a few cases, megaloblastic anemia has been associated with the chronic use of phenobarbital.

Other:

Nausea and vomiting; headache.

To report SUSPECTED ADVERSE REACTIONS, contact Winder Laboratories, LLC at 1-770-307-0703, or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

The signs and symptoms of barbiturate poisoning are referable especially to the central nervous system and the cardiovascular system. Moderate intoxication resembles alcoholic inebriation. In severe intoxication, the patient is comatose, the level of reflex activity conforming in a general way to the intensity of the central depression. The deep reflexes may persist for some time despite coexistent coma. The Babinski sign is often positive. The EEG may be of the "burst-suppression" type, with brief periods of electrical silence. The pupils may be constricted and react to light, but late in the course of barbiturate poisoning they may show hypoxic paralytic dilatation. Respiration is affected early.

Breathing may be either slow or rapid and shallow; Cheyne-Stokes rhythm may be present. Respiratory minute volume is diminished, and hypoxia and respiratory acidosis may develop. The blood pressure falls, owing partly to depression of medullary vasomotor centers; partly to a direct action of the drug on the myocardium, sympathetic ganglia, and vascular smooth muscle; partly to hypoxia.

The patient thus develops a typical shock syndrome, with a weak and rapid pulse, cold and clammy skin, and a rise in the hematocrit. Respiratory complications (atelectasis, pulmonary edema, and bronchopneumonia) and renal failure are much dreaded and not infrequent concomitant of severe barbiturate poisoning. There is usually hypothermia, sometimes with temperatures as low as 32°C.

Oral Sedative Dose, Adults:30 to 120 mg daily in 2 or 3 divided doses.

Children:6 mg/kg of body weight daily in 3 divided doses.

Oral Hypnotic Dose, Adults:100 to 320 mg.

Oral Anticonvulsant Dose, Adults:50 to 100 mg 2 or 3 times daily.

Children:15 to 50 mg 2 or 3 times daily.

Phenobarbital Tablets, USP 15 mg:

White, Round Tablet; Debossed WL on one side and 136 on the other side.

Phenobarbital Tablets, USP 16.2 mg (¼ grain):

White, Round, Scored Tablet; Debossed WL on one side and 137 on the other side.

Phenobarbital Tablets, USP 30 mg:

White, Round, Scored Tablet; Debossed WL on one side and 138 on the other side.

Phenobarbital Tablets, USP 32.4 mg (½ grain):

White, Round, Scored Tablet; Debossed WL on one side and 139 on the other side.

Phenobarbital Tablets, USP 60 mg:

White, Round Tablet; Debossed WL on one side and 140 on the other side.

Phenobarbital Tablets, USP 64.8 mg (1 grain):

White, Round, Scored Tablet; Debossed WL on one side and 141 on the other side.

Phenobarbital Tablets, USP 97.2 mg (1½ grain):

White, Round, Scored Tablet; Debossed WL on one side and 142 on the other side.

Phenobarbital Tablets, USP 100 mg:

White, Round, Scored Tablet; Debossed WL on one side and 143 on the other side.

Manufactured by:
Winder Laboratories, LLC.
Winder, GA 30680

RLS.135.99-1.0
Updated: Jan 2022