Skip to Content


Generic Name: trimethadione (TRYE meth a DYE one)
Brand Name: Tridione

What is trimethadione?

Trimethadione is an anti-epileptic medication, also called an anticonvulsant.

Trimethadione is used to treat absence seizures (also called "petit mal" seizures) in adults and children.

Trimethadione is usually given after other seizure medicines have been tried without success.

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

What is the most important information I should know about trimethadione?

You should not stop using trimethadione suddenly. Stopping suddenly may make your condition worse.

Slideshow: Need To Know: Top 9 Facts About Gabapentin

What should I discuss with my healthcare provider before taking trimethadione?

You should not use trimethadione if you are allergic to it.

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

  • liver disease;

  • kidney disease;

  • depression, a mood disorder, or history of suicidal thoughts or actions;

  • eye problems;

  • a blood cell disorder such as anemia or low white blood cells;

  • lupus; or

  • myasthenia gravis (a nerve-muscle disorder).

You may have thoughts about suicide while taking this medicine. Tell your doctor if you have new or worsening depression or suicidal thoughts during the first several months of treatment, or whenever your dose is changed. Your family or other caregivers should also be alert to changes in your mood or symptoms.

This medicine can harm an unborn baby or cause birth defects. Do not use trimethadione if you are pregnant. Use effective birth control to prevent pregnancy while you are using this medicine.

If you are pregnant, your name may be listed on a pregnancy registry. This is to track the outcome of the pregnancy and to evaluate any effects of trimethadione on the baby.

Do not start or stop taking trimethadione during pregnancy without your doctor's advice. Trimethadione may cause harm to an unborn baby, but having a seizure during pregnancy could harm both mother and baby. Tell your doctor right away if you become pregnant. You may need to use a different seizure medicine.

If you have taken this medicine during pregnancy, be sure to tell the doctor who delivers your baby about your trimethadione use. Both you and the baby may need to receive medications to prevent excessive bleeding during delivery and just after birth.

It is not known whether trimethadione 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 trimethadione?

Follow all directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results. Do not use this medicine in larger or smaller amounts or for longer than recommended.

The chewable tablet may be chewed or swallowed whole.

While using trimethadione, you may need frequent blood and urine tests. You must remain under the care of a doctor while taking this medicine.

Do not stop using trimethadione suddenly, even if you feel fine. Stopping suddenly may cause increased seizures. Follow your doctor's instructions about tapering your dose.

Store in the refrigerator, do not freeze. Keep the bottle tightly closed when not in use.

Read all patient information, medication guides, and instruction sheets provided to you. Ask your doctor or pharmacist if you have any questions.

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 at 1-800-222-1222.

What should I avoid while taking trimethadione?

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

Do not drink alcohol while taking this medicine.

Trimethadione side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, hyperactive (mentally or physically), more depressed, or have thoughts about suicide or hurting yourself.

Call your doctor at once if you have:

  • vision problems, droopy eyelids;

  • the first sign of any skin rash, no matter how mild;

  • unusual muscle weakness, trouble speaking or swallowing;

  • swelling in your feet or ankles;

  • low blood cell counts--fever, chills, flu-like symptoms, swollen gums, mouth sores, skin sores, rapid heart rate, pale skin, easy bruising, unusual bleeding, feeling light-headed;

  • lupus-like syndrome--joint pain or swelling with fever, swollen glands, muscle aches, chest pain, butterfly-shaped skin rash on your cheeks;

  • kidney problems--little or no urinating, painful or difficult urination, rapid weight gain;

  • liver problems--nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); 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.

Common side effects may include:

  • nausea;

  • drowsiness;

  • changes in mood or behavior; or

  • increased seizures.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

See also: Side effects (in more detail)

Trimethadione dosing information

Usual Adult Dose for Seizures:

-Initial dose: 900 mg orally per day in equally divided doses 3 to 4 times a day; increase this dose by 300 mg at weekly intervals until therapeutic results are seen or until toxic symptoms appear
-Maintenance dose: 900 to 2400 mg orally per day in 3 or 4 equally divided doses (i.e., 300 to 600 mg orally 3 or 4 times a day

-Maintenance dosage should be the least amount of drug required to maintain control.

Use: For the control of petit mal seizures that are refractory to treatment with other drugs

Usual Pediatric Dose for Seizures:

300 to 900 mg orally per day in 3 or 4 equally divided doses

Use: For the control of petit mal seizures that are refractory to treatment with other drugs

What other drugs will affect trimethadione?

Taking this medicine with other drugs that make you sleepy can worsen this effect. Ask your doctor before taking trimethadione with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety or depression.

Other drugs may interact with trimethadione, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.

Where can I get more information?

  • Your pharmacist can provide more information about trimethadione.
  • Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
  • Disclaimer: Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2012 Cerner Multum, Inc. Version: 1.01. Revision Date: 2015-09-14, 7:55:07 PM.