In the U.S.—

In Canada—

• Anticonvulsant

Primidone ( PRYE-mih-done) belongs to the group of medicines called anticonvulsants. It is used in the treatment of epilepsy to manage certain types of seizures. Primidone may be used alone or in combination with other anticonvulsants. It acts by controlling nerve impulses in the brain.

Primidone is available only with your doctor's prescription, in the following dosage forms:

Oral
• Suspension (U.S.)
• Tablets (U.S. and Canada)
• Chewable tablets (Canada)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For primidone, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to primidone or to any barbiturate medicine (for example, amobarbital, butabarbital, pentobarbital, phenobarbital, secobarbital). Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Although most mothers who take medicine for seizure control deliver normal babies, there are reports of increased birth defects when these medicines are used during pregnancy. Newborns whose mothers were taking primidone during pregnancy have been reported to have bleeding problems. It is not definitely known if any of these medicines are the cause of such problems.

Breast-feeding—Primidone passes into the breast milk and may cause unusual drowsiness in nursing babies. It may be necessary for you to take another medicine or to stop breast-feeding during treatment. Be sure you have discussed the risks and benefits of the medicine with your doctor.

Children—Unusual excitement or restlessness may occur in children, who are usually more sensitive than adults to these effects of primidone.

Older adults—Unusual excitement or restlessness may occur in elderly patients, who are usually more sensitive than younger adults to these effects of primidone.

Other medicines—Although certain medicines should not be used together at all, in other cases 2 different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking primidone it is especially important that your health care professional know if you are taking any of the following:

• Adrenocorticoids (cortisone-like medicines) or
• Anticoagulants (blood thinners)—Use with primidone may decrease the effects of these medications, and the amount of medicine you need to take may change

• Central nervous system (CNS) depressants (medicine that causes drowsiness)—Using these medicines with primidone may increase the CNS and other depressant effects

• Oral contraceptives (birth control pills) containing estrogen—Primidone may decrease the effectiveness of these oral contraceptives, and you may need to change to a different type of birth control

• Other anticonvulsants (seizure medicine)—A change in the pattern of seizures may occur; close monitoring of blood levels of both medications is recommended. Use of valproic acid with primidone may cause increased CNS depression and other serious side effects

• Monoamine oxidase (MAO) inhibitor activity (isocarboxazid [e.g., Marplan], phenelzine [e.g., Nardil], procarbazine [e.g., Matulane], selegiline [e.g., Eldepryl], tranylcypromine [e.g., Parnate])—Taking primidone while you are taking or within 2 weeks of taking monoamine oxidase (MAO) inhibitors may prolong the effects of primidone and may change the pattern of seizures

• Asthma, emphysema, or chronic lung disease—Primidone may cause serious problems in breathing

• Hyperactivity (in children) or
• Kidney disease or
• Liver disease—Primidone may make the condition worse

• Porphyria—Primidone should not be used when this medical problem exists because it may make the condition worse

Take primidone every day in regularly spaced doses as ordered by your doctor . This will provide the proper amount of medicine needed to prevent seizures.

Dosing—

The dose of primidone will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of primidone. If your dose is different, do not change it unless your doctor tells you to do so.

The number of tablets or teaspoonfuls of suspension that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on your special needs.

• For oral dosage forms (chewable tablets, tablets or suspension):
  • For epilepsy:
    • Adults, teenagers, and children 8 years of age or older—At first, 100 or 125 milligrams (mg) once a day at bedtime. Your doctor may increase your dose if needed. However, the dose is usually not more than 2000 mg a day.
    • Children up to 8 years of age—At first, 50 mg once a day at bedtime. Your doctor may increase your dose if needed.

Missed dose—

If you miss a dose of this medicine, take it as soon as possible. However, if it is within an hour of your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store the tablet form of this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Keep the liquid form of this medicine from freezing.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

It is very important that your doctor check your progress at regular visits, especially during the first few months of treatment with primidone. This will allow your doctor to adjust the amount of medicine you are taking to meet your needs.

If you have been taking primidone regularly for several weeks, you should not suddenly stop taking it. Your doctor may want you to reduce gradually the amount you are taking before stopping completely.

Before you have any medical tests, tell the medical doctor in charge that you are taking this medicine. The results of some tests (such as the metyrapone and phentolamine tests) may be affected by this medicine.

Before having any kind of surgery, dental treatment, or emergency treatment, tell the medical doctor or dentist in charge that you are using this medicine.

This medicine will add to the effects of alcohol and other CNS depressants (medicines that cause drowsiness). Some examples of CNS depressants are antihistamines or medicine for hay fever, other allergies, or colds; sedatives, tranquilizers, or sleeping medicine; prescription pain medicine or narcotics; barbiturates; medicine for seizures; muscle relaxants; or anesthetics, including some dental anesthetics. Check with your doctor before taking any of the above while you are using this medicine.

Primidone may cause some people to become dizzy, lightheaded, drowsy, or less alert than they are normally. Even if taken at bedtime, it may cause some people to feel drowsy or less alert on arising. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert .

Oral contraceptives (birth control pills) containing estrogen may not work properly if you take them while you are taking primidone. Unplanned pregnancies may occur. You should use a different or additional means of birth control while you are taking primidone. If you have any questions about this, check with your health care professional.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor if any of the following side effects occur:

• Less common
  • Unusual excitement or restlessness (especially in children and in the elderly) 
  
  

• Rare
  • Skin rash;  unusual tiredness or weakness  
  
  

• Symptoms of overdose
  • Confusion;  continuous, uncontrolled back-and-forth and/or rolling eye movements;  double vision;  shortness of breath or troubled breathing  
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common
  • Clumsiness or unsteadiness;  dizziness  
  
  

• Less common
  • Decreased sexual ability;  drowsiness ;  loss of appetite;  mood or mental changes;  nausea or vomiting 
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although this use is not included in product labeling, primidone is used in certain patients with the following medical conditions:

• Essential tremor

Other than the above information, there is no additional information relating to proper use, precautions, or side effects for these uses.