What is phenobarbital?

Phenobarbital is a barbiturate (bar-BIT-chur-ate). Phenobarbital slows the activity of your brain and nervous system.

Phenobarbital is used to treat or prevent seizures. Phenobarbital is also used short-term as a sedative to help you relax.

Phenobarbital may also be used for purposes not listed in this medication guide.

Phenobarbital side effects

Phenobarbital may cause a severe allergic reaction. Stop taking phenobarbital and get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, eyes, lips, tongue, or throat.

Phenobarbital may cause serious side effects. Call your doctor at once if you have:

• weak or shallow breathing;
• unusual pain anywhere in your body (especially in the neck, shoulder, or arms);
• a red blood cell disorder–pale skin, muscle weakness, diarrhea, weight loss, rapid heart rate, tongue swelling, numbness or tingling in your hands or feet, feeling short of breath; or
• severe skin reaction–fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Side effects such as confusion, depression, or excitement may be more likely in older adults and those who are ill or debilitated.

Common side effects of phenobarbital may include:

• drowsiness, lack of energy;
• dizziness or spinning sensation;
• depressed mood;
• feeling restless or excited (especially in children or older adults);
• drunk feeling; or
• “hangover” effect (drowsiness the day after taking phenobarbital).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

Warnings

You should not use phenobarbital if you have severe liver disease, severe asthma or COPD, a personal or family history of porphyria, or a history of addiction to drugs similar to phenobarbital.

Before taking this medicine

You should not take phenobarbital if you are allergic to phenobarbital or other barbiturates (Nembutal, Seconal, and others), or if you have:

• severe asthma, chronic obstructive pulmonary disorder (COPD), or other breathing disorder;
• a personal or family history of porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system);
• severe liver disease; or
• a history of addiction to phenobarbital or similar medicines (Valium, Xanax, Ativan, and others).

To make sure phenobarbital is safe for you, tell your doctor if you have:

• liver disease;
• temporary or chronic pain;
• a pituitary gland disorder;
• pheochromocytoma (tumor of the adrenal gland);
• kidney disease;
• a food or drug allergy;
• a condition for which you take a blood thinner (warfarin, Coumadin, Jantoven).

Follow your doctor’s instructions about taking seizure medication if you are pregnant. Seizure control is very important during pregnancy, and having a seizure could harm both mother and baby. Do not start or stop taking this medicine without your doctor’s advice, and tell your doctor right away if you become pregnant.

Phenobarbital can make birth control pills less effective. Ask your doctor about using a non-hormonal birth control (condom, diaphragm with spermicide) to prevent pregnancy.

It is not known whether phenobarbital passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

How should I take phenobarbital?

Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Phenobarbital may be habit-forming. Never share phenobarbital with another person, especially someone with a history of drug abuse or addiction. Keep the medication in a place where others cannot get to it. Selling or giving away this medicine is against the law.

Do not change your phenobarbital dose without your doctor’s advice. Tell your doctor if the medicine does not seem to work as well in treating your condition.

If you are taking phenobarbital to treat seizures, keep taking the medicine even if you feel fine.

Do not stop using suddenly after long-term use, or you could have unpleasant withdrawal symptoms. Ask your doctor how to safely stop using phenobarbital.

Store at room temperature away from moisture, heat, and light.

Keep track of the amount of medicine used from each new bottle. Phenobarbital is a drug of abuse and you should be aware if anyone is using your medicine improperly or without a prescription.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line . An overdose of phenobarbital can be fatal.

Overdose symptoms may include slow or shallow breathing, weak pulse, cold or clammy skin, little or no urination, pinpoint pupils, feeling cold, or fainting.

What should I avoid while taking phenobarbital?

Drinking alcohol with phenobarbital can cause side effects.

This medication may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

What other drugs will affect phenobarbital?

Taking this medicine with other drugs that make you sleepy or slow your breathing can cause dangerous or life-threatening side effects. Ask your doctor before taking phenobarbital with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures.

What is primidone?

Primidone is an anticonvulsant that is used alone or with other medications to control seizures in adults and children.

Primidone may also be used for purposes not listed in this medication guide.

Primidone side effects

Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Tell your doctor right away if you have new or sudden changes in mood or behavior, including new or worse depression or anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, more active or talkative, or have thoughts about suicide or hurting yourself.

Primidone may cause serious side effects. Call your doctor at once if you have:

• extreme drowsiness, falling asleep suddenly, even after feeling alert; or
• signs of infection–fever, swollen glands, shortness of breath, chills, sore throat, body aches, unusual tiredness, loss of appetite, bruising or bleeding.

Common side effects of primidone may include:

• dizziness, drowsiness, vertigo (spinning sensation);
• problems with walking or moving;
• nausea, vomiting, loss of appetite;
• feeling tired or irritable;
• vision problems; or
• impotence, sexual problems.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

Warnings

Some people have thoughts about suicide while taking seizure medicine. Tell your doctor right away if you have any sudden changes in mood or behavior, or thoughts about suicide.

Seizures may increase if you stop using primidone suddenly. Ask your doctor before stopping the medicine.

Before taking this medicine

You should not use primidone if you have:

• an allergy to phenobarbital; or
• porphyria (a genetic disorder that causes symptoms affecting the skin or nervous system).

Tell your doctor if you have ever had:

• depression;
• a mood disorder; or
• suicidal thoughts or actions.

Some people have thoughts about suicide while taking seizure medicine. Stay alert to changes in your mood or symptoms. Your family or caregivers should also watch for sudden changes in your behavior.

Do not start or stop seizure medication during pregnancy without your doctor’s advice. Having a seizure during pregnancy could harm both mother and baby. Tell your doctor if you become pregnant.

If you take primidone during pregnancy, be sure to tell the doctor who delivers your baby. Both you and the baby may need medication to prevent bleeding during delivery and just after birth.

If you are pregnant, your name may be listed on a pregnancy registry to track the effects of primidone on the baby.

Tell your doctor if you are breastfeeding. If you are breastfeeding, tell your doctor if you notice drowsiness in the nursing baby.

How should I take primidone?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

You may not fully benefit from this medicine for up to several weeks. Your doctor will determine how long to treat you with this medicine.

You should not stop using primidone suddenly. Seizures may increase if you stop using primidone. Ask your doctor before stopping the medicine.

You may need blood tests, and your next dose may be changed based on the results. Your doctor will need to check your progress on a regular basis.

You may be given other medications such as folic acid to help prevent serious side effects. Keep taking these medicines for as long as your doctor has prescribed.

Doses may be based on weight for children under 8 years old. Your child’s dose may change if the child gains or loses weight.

Store tightly closed at room temperature, away from moisture and heat.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line .

What should I avoid while taking primidone?

Avoid driving or hazardous activity until you know how primidone will affect you. Your reactions could be impaired.

Drinking alcohol with this medicine can cause side effects.

What other drugs will affect primidone?

Using primidone with other drugs that make you drowsy can worsen this effect. Ask your doctor before using opioid medication, a sleeping pill, a muscle relaxer, or medicine for anxiety or seizures.