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pronounced as (trye meth a dye' one)

Why is this medication prescribed?

Trimethadione is used to control absence seizures (petit mal; a type of seizure in which there is a very short loss of awareness during which the person may stare straight ahead or blink his eyes and does not respond to others) when other medications will not work. Trimethadione is in a class of medications called anticonvulsants. It works by reducing abnormal electrical activity in the brain.

How should this medicine be used?

Trimethadione comes as a chewable tablet to take by mouth. It is usually taken three or four times a day. Take trimethadione at around the same times every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take trimethadione exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

The chewable tablets may be chewed or swallowed whole.

Trimethadione may help to control your condition but will not cure it. Continue to take trimethadione even if you feel well. Do not stop taking trimethadione without talking to your doctor. Your doctor probably will decrease your dose gradually. If you suddenly stop taking trimethadione, your seizures may become worse.

Your doctor or pharmacist will give you the manufacturer's patient information sheet (Medication Guide) when you begin treatment with trimethadione and each time you refill your prescription. Read the information carefully and ask your doctor or pharmacist if you have any questions. You can also visit the Food and Drug Administration (FDA) website ( to obtain the Medication Guide.

Other uses for this medicine

This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.

What special precautions should I follow?

Before taking trimethadione,

  • tell your doctor and pharmacist if you are allergic to trimethadione, any other medications, or any of the ingredients of trimethadione tablets. Ask your pharmacist or check the Medication Guide for a list of the ingredients.
  • tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention medications for colds or allergies; medications for depression; medications for pain; other medications for seizures; sedatives; sleeping pills; or tranquilizers. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
  • tell your doctor if you have or have ever had , a blood disorder, depression, mood problems, suicidal (thinking about harming or killing yourself or planning or trying to do so) thoughts or behavior, or eye, kidney, or liver disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. Women who can become pregnant generally should not take trimethadione. However, you and your doctor may decide that trimethadione is needed to treat your condition. In that case you must: talk to your doctor about birth control methods that you can use during your treatment. If you become pregnant while using this medication, call your doctor. Trimethadione may harm the fetus.
  • if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking trimethadione.
  • you should know that this drug may make you dizzy or drowsy. Do not drive a car or operate machinery until you know how this drug affects you.
  • avoid use of alcoholic beverages while you are taking trimethadione. Alcohol may make the side effects from trimethadione worse.
  • you should know that your mental health may change in unexpected ways and you may become suicidal while you are taking trimethadione. A small number of adults and children 5 years of age and older (about 1 in 500 people) who took anticonvulsants such as trimethadione to treat various conditions during clinical studies became suicidal during their treatment. Some of these people developed suicidal thoughts and behavior as early as one week after they started taking the medication. There is a risk that you may experience changes in your mental health if you take an anticonvulsant medication such as trimethadione, but there may also be a risk that you will experience changes in your mental health if your condition is not treated. You and your doctor will decide whether the risks of taking an anticonvulsant medication are greater than the risks of not taking the medication. You, your family, or your caregiver should call your doctor right away if you experience any of the following symptoms: panic attacks; agitation or restlessness; new or worsening irritability, anxiety, or depression; acting on dangerous impulses; difficulty falling or staying asleep; aggressive, angry, or violent behavior; mania (frenzied, abnormally excited mood); talking or thinking about wanting to hurt yourself or to end your life; withdrawing from friends and family; preoccupation with death and dying; giving away prized possessions; or any other unusual changes in behavior or mood. Be sure that your family or caregiver knows which symptoms may be serious so they can call the doctor if you are unable to seek treatment on your own.

What special dietary instructions should I follow?

Unless your doctor tells you otherwise, continue your normal diet.

What should I do if I forget a dose?

Take the missed dose as soon as you remember it. However, if you remember a missed dose at the time you are scheduled to take the next dose, skip the missed dose completely. Do not take a double dose to make up for a missed one.

What side effects can this medication cause?

Trimethadione may cause side effects. Tell your doctor if any of these symptoms or those listed in the SPECIAL PRECAUTIONS section are severe or do not go away:

  • tiredness
  • changes in weight
  • hiccups
  • headache
  • numbness, burning, or tingling in the hands, arms, feet, or legs
  • difficulty falling asleep or staying asleep
  • hair loss

Some side effects can be serious. If you experience any of these symptoms , call your doctor immediately:

  • difficulty coordinating movements
  • sensitivity to the sun
  • joint or muscle pain
  • chest pain or shortness of breath
  • swelling of your feet, ankles, or legs
  • weakness of your arms or legs
  • difficulty swallowing
  • speech problems
  • rash on the cheeks or other parts of the body
  • hives
  • sores in the mouth
  • easy bruising
  • red- or purple-colored skin spots
  • bloody nose
  • bleeding gums
  • unusual bleeding
  • extreme weakness or tiredness
  • yellowing of the skin or eyes
  • dark urine
  • nausea or vomiting
  • loss of appetite
  • pain in the upper right part of the stomach
  • fever
  • swollen glands
  • sore throat
  • decreased urination
  • droopy eyelids
  • blurred vision
  • problems seeing in bright light
  • seizures

Trimethadione may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online ( or by phone (1-800-332-1088).

What should I know about storage and disposal of this medication?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store trimethadione chewable tablets in the refrigerator.

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website ( for more information if you do not have access to a take-back program.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach.

In case of emergency/overdose

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

Symptoms of overdose may include:

  • drowsiness
  • nausea
  • dizziness
  • difficulty coordinating movements
  • changes in vision
  • coma (loss of consciousness for a period of time)

What other information should I know?

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your response to trimethadione.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

Brand names

  • Tridione®
Last Revised - 06/15/2018