Primidone belongs to the class of medications known as anticonvulsants. It is indicated for the control of seizures in the treatment of epilepsy and other seizure disorders. Primidome may be prescribed alone or as part of a combination of medications for preventing seizures.
Primidone is thought to decrease abnormal activity within the brain that may trigger seizures. While primidone controls some types of seizures associated with epilepsy (grand mal, psychomotor, and focal seizures) there is no known cure for the disorder. Additionally, primidone has shown promise in alleviating some forms of essential tremors, but is not approved in the United States for this use.
In the United States, primidone is also sold under the names Myidone and Mysoline. Although the precise mechanism by which primidone exerts its therapeutic effects is unknown, it is thought to help slow and control nerve impulses in the brain. The active metabolites of primidone are phenobarbital and phenylmethylmalonamide (PEMA), both barbiturate-type compounds with anticonvulsant and sedative properties. Primidone is supplied in chewable tablets (in Canada), tablets to be swallowed whole, and in suspension (syrup) forms for oral administration.
Primidone is available in 50 milligram (mg) and 250 mg tablets, and is prescribed by physicians in varying dosages. The usual initial dose for adults, teenagers, and children over eight years of age is 100 mg or 125 mg per day. Dosages are gradually increased until arriving at the lowest possible dosage that results in control of seizures. Children under eight years of age typically take an initial daily dose of 50 mg. The maximum daily dose for anyone taking primidone usually is not greater than 2000 mg.
The prescribing physician will schedule a patient's daily dosages, gradually increasing them over the course of several weeks. Primidone may not exert its full therapeutic effect during the initial dose-increasing period.
Primidone should be taken at approximately the same time every night. If a daily dose is missed, it should be taken as soon as possible. However, if it is almost time for the next dose, the missed dose should be skipped. Double doses of primidone should not be taken.
A patient should consult their physician before they stop taking primidone. Suddenly discontinuing this medicine may cause seizures to return or occur more frequently. When ending treatment including primidone, physicians typically direct patients to taper their daily dosages gradually.
A physician should be consulted before taking primidone with non-prescription medications. Patients should avoid alcohol and CNS depressants (medicines that can make one drowsy or less alert, such as antihistimines, sleep medications, and some pain medications) while taking primidone because it can exacerbate their side effects. Primidone may not be suitable for persons with a history of porphyria, asthma or other chronic lung diseases, liver disease, kidney disease, mental illness, high blood presure, angina (chest pain), irregular heartbeats, or other heart problems. Patients should notify their physician if they consume a large amount of alcohol, have a history of drug use, are pregnant, or plan to become pregnant.
Anticonvulsant medications, namely phentoyn and phenobarbital, have been shown to cause birth defects. Physicians usually advise women of childbearing age to use effective birth control while taking this medication. Patients who become pregnant while taking primidone should contact their physician immediately.
Patients and their physicians should weigh the risks and benefits of primidone before beginning treatment. Most patients tolerate primidone well, but may experience a variety of mild side effects. If any symptoms persist or become too uncomfortable, consult the prescribing physician. The following common side effects usually do not require medical attention and may lessen after taking primidone for several weeks:
- dizziness, unsteadiness, or clumsiness
- nausea or vomiting
- decreased sexual desire or ability
- loss of appetite
- mood or mental changes
Other, less common side effects of primidone may be serious. Contact a physician immediately if any of the following symptoms occur:
- rash or bluish patches on the skin
- unusual excitement or restlessness (espeically in children, seniors, or patients taking high dosages)
- double vision
- uncontrolled back-and-forth or rolling eye movements
- speech or language problems
- chest pain
- irregular heartbeat
- faintness or loss of consciousness
- persistent, severe headaches
- persistent fever or pain.
Primidone may have negative interactions with adrenocorticoids (cortisone-like medications), antibiotics, antidepressants, anticoagulants, antihistimines, asthma medications, barbituates, and monoamine oxidase inhibitors (MAOIs). Primidone should be used in conjunction with other seizure prevention medications, especially valproic acid, only if advised and closely monitored by a physician. Primidone may decrease the effectiveness of oral contraceptives (birth control pills) that contain estrogen.
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Weaver, Donald F. Epilepsy and Seizures: Everything You Need to Know. Toronto: Firefly Books, 2001.
"Primidone (systemic)." Thompson Micromedex. <http://health.yahoo.com/health/drug/202479/> (April 4, 2004).
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American Epilepsy Society. 342 North Main Street, West Hartford, CT 06117-2507. <http://www.aesnet.org>.
Epilepsy Foundation, 4351 Garden City Drive, Landover, MD 20785-7223. (800) 332-1000. <http://www.epilepsyfoundation.org>.
Adrienne Wilmoth Lerner