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Overview: Methsuximide is used to control certain types of seizures when other medicines have not worked. Common side effects include drowsiness, dizziness, headache, blurred vision, nausea, vomiting, diarrhea, constipation, upset stomach, weight loss, and trouble with balance and coordination. Do not drive or do other activities that require alertness or coordination until you know how methsuximide affects you. Tell your health care provider right away if you get a rash, sore throat, or a fever. 

Uses

What is methsuximide used for?

Methsuximide is used to control certain types of seizures when other medicines have not worked.

Methsuximide may also be used for other conditions as determined by your health care provider.

How does methsuximide work (mechanism of action)?

A seizure happens when electrical and chemical brain signals suddenly become too active. Methsuximide works by helping calm down unusual brain activity to prevent seizures.

How is methsuximide supplied (dosage forms)?

Brands and other names

  • Celontin

Dosage forms and strengths

  • 300 mg oral capsules

How should I store methsuximide?

Methsuximide should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Protect from moisture, light, and excessive heat.

Side Effects

What are the most common side effects of methsuximide?

The most common side effects of methsuximide are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Drowsiness 
  • Dizziness
  • Headache
  • Blurred vision
  • Nausea, vomiting, and diarrhea
  • Constipation 
  • Upset stomach
  • Weight loss
  • Trouble with balance and coordination 

There may be other side effects of methsuximide that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of methsuximide?

While less common, the most serious side effects of methsuximide are described below, along with what to do if they happen.

Blood Disorders. Methsuximide can cause blood disorders, such as pancytopenia, and low white blood cell levels (leukopenia). Call your health care provider right away if you have any of the following symptoms of blood disorders.

  • Fever
  • Shortness of breath
  • Pale or yellowish skin
  • Easy bruising or bleeding
  • Frequent infection
  • Sore throat
  • Unusual weakness or tiredness
  • Dizziness, lightheadedness, or feeling like you are about to pass out
  • Headache
  • Fast or abnormal heartbeat

Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking methsuximide. Call your health care provider right away if you have any of the following symptoms of liver damage.

  • Nausea or vomiting
  • Stomach or belly pain
  • Fever
  • Weakness or unusual tiredness
  • Itching
  • Loss of appetite
  • Light-colored poop
  • Dark-colored urine (pee)
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Lupus-like Symptoms. Methsuximide can cause symptoms that look like a condition called lupus. Call your health care provider right away if you have any of the following symptoms.

  • Rash
  • Joint pain
  • Fever
  • Weakness or unusual tiredness
  • Swollen glands
  • Reduced need to pee
  • Pink, red, or brown pee
  • Swelling

Suicidal Thoughts and Actions. Methsuximide may cause suicidal thoughts or actions in a small number of people. If you are about to harm yourself, call 911 or call or text 988, the Suicide & Crisis Lifeline. Call your health care provider right away if you have any of the following symptoms.

  • New or increased thoughts of suicide or death
  • Suicide attempt
  • New or increased feelings of anxiety, depression, or other unusual changes in mood or behavior

Severe Skin Reactions. Methsuximide can cause severe skin reactions, called Stevens-Johnson syndrome (SJS), that can lead to death if not treated. If you have a rash, call your health care provider right away. Get emergency help if you have any of the following symptoms of SJS.

  • Painful red or purple skin that looks burned and peels off
  • Flat red rash or blisters on your skin, mouth, nose, and genitals
  • Red, painful, watery eyes
  • Flu-like symptoms including fever, chills, and muscle aches

Severe Allergic Reactions. Methsuximide may cause allergic reactions, which can be serious. Stop taking methsuximide and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Warnings & Precautions

Who should not use methsuximide?

Allergies to Ingredients. People who are allergic to any of the following should not take methsuximide.

  • Celontin
  • Methsuximide
  • Any other medicine known as a succinimides
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific methsuximide products they stock.

What should I know about methsuximide before using it?

Do not take methsuximide unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share methsuximide with other people, even if they have the same condition as you. It may harm them.

Keep methsuximide out of the reach of children.

Do not stop taking methsuximide without talking to your health care provider. Stopping methsuximide suddenly could lead to increased seizures and increase your risk of having status epilepticus, which is a seizure that lasts more than five minutes. If you need to stop taking methsuximide, your health care provider can tell you how to slowly stop the medicine.

Your health care provider will likely obtain lab work while you are taking this medicine to watch for signs of liver, kidney, or blood problems. Keep all appointments, including those for lab work, while you are taking this medicine. 

Methsuximide can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how methsuximide affects you.

What should I tell my health care provider before using methsuximide?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if methsuximide is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Blood disorders
  • Depression, mood problems, suicidal thoughts or behavior, or a history of these conditions
  • Liver or kidney problems
  • Lupus

Other Medicines and Supplements. Methsuximide may interact with other medicines and supplements. Before taking methsuximide, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how methsuximide could affect pregnancy or harm an unborn baby. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should take methsuximide while you are pregnant or trying to get pregnant. If you become pregnant while taking methsuximide, you can sign up for the North American Antiepileptic Drug Pregnancy Registry by calling 888-233-2334 or at www.aedpregnancyregistry.org. This registry collects safety information about the use of seizure medicines during pregnancy.

Breastfeeding. It is not known if methsuximide passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take methsuximide while breastfeeding.

Interactions

Does methsuximide interact with foods or drinks?

There are no known interactions between methsuximide and foods or drinks. 

Do not drink alcohol while taking methsuximide. The risk of drowsiness and dizziness may be increased if you drink alcohol while taking methsuximide.

Does methsuximide interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss with your health care provider if you are using any of the following before taking methsuximide.

  • Phenytoin (Dilantin, Phenytek, and others), which is a medicine to control seizures
  • Phenobarbital, which is a medicine that may be used to treat seizures
  • Any medicine that causes dizziness and sleepiness, such as prescription pain medicines, sleep medicines, or medicines for anxiety

This may not be a complete list of medicines that can interact with methsuximide. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much methsuximide?

If you or someone else has used too much methsuximide, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of methsuximide?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.