Phenobarbital: what it is for, how to take it and side effects

Phenobarbital is a barbiturate medication indicated for the treatment of seizures and epilepsy, as it has anticonvulsant and sedative properties, which act directly on the brain.

This medicine can be found in pharmacies or drugstores, in the form of 50 mg and 100 mg tablets, or an oral solution (drops) of 40 mg/mL, under the trade name Gardenal, or in its generic form, under the name “phenobarbital “, sold only upon presentation of a medical prescription.

Phenobarbital should only be used with medical advice and can also be offered free of charge by the SUS. Furthermore, phenobarbital can be found in hospitals in the form of an injection, administered by nurses, under medical supervision.

What is it for

Phenobarbital is normally indicated for the treatment of seizures and epilepsy due to its anticonvulsant properties.

Although there are no other indications in the leaflet, in some cases, the doctor may recommend the use of phenobarbital to treat insomnia, during the suspension of benzodiazepine medications and in case of intracranial hypertension due to blows and accidents, for example.

How to drink

Phenobarbital must be taken orally, the tablets must be taken with a glass of water, and the oral solution must be diluted in a little water.

The doses of phenobarbital indicated for the treatment of children and adults are different and vary as follows:

1. Doses for children

The initial dose of phenobarbital in children varies from 1 to 3 mg/kg/day, which can be given in a single or divided dose, and must be calculated by the pediatrician.

Normally, a slow increase in dose up to 3 mg/kg/day is indicated, which is the maintenance dose of the medication. Furthermore, depending on the control of convulsive crises, the dose can be increased to a maximum of 8 mg/kg/day.

2. Doses for adults

The initial doses of phenobarbital for adults are 2 to 3 mg/kg/day, calculated by the neurologist or general practitioner and, depending on the control of seizures, the dose can be changed by the doctor after 15 days of treatment.

Possible side effects

The main side effects of phenobarbital are:

• Somnolence;
• Difficulty concentrating;
• Lack of motor coordination;
• Mood changes, such as depression;
• Difficulty with balance;
• Hyperactivity in children.

Side effects are more common in elderly people and when phenobarbital is used in high doses. Furthermore, when used for long periods, bone fragility, loss of appetite, muscle or joint pain and liver damage, for example, can also occur.

Other known side effects involve symptoms such as nausea, vomiting, anxiety, nightmares, dizziness and headache. Sometimes phenobarbital can also cause symptoms such as slowed heart rate or low blood pressure.

Rarely, the use of phenobarbital can cause serious reactions such as allergies and Stevens-Johnson syndrome.

Who shouldn’t use

Phenobarbital should not be used in case of allergic reactions to barbiturate medications, illnesses causing severe liver, kidney or respiratory failure, or pregnancy. Furthermore, use should also be avoided if there is a history of porphyria or abusive use of sedative medications and in case of use of some antiviral medications.

When used by women taking hormonal contraceptives, phenobarbital may decrease the effectiveness of the contraceptive, increasing the risk of pregnancy. In the case of breastfeeding women, the use of phenobarbital can cause drowsiness and difficulty sucking in the baby. Therefore, phenobarbital is also not indicated in these situations.