Methsuximide (Oral)

Methsuximide is used in the treatment of epileptic patients to prevent seizures where other drugs have been ineffective.


In the US, methsuximide is known under the brand name, Celontin Kapseals. It is a prescription only medicine that comes in capsule form for oral dosage.

Methsuximide is one of a family of drugs called anticonvulsants. The medication is used to control petit mal (absence) seizures in patients who suffer from epilepsy. This drug is only used after other similar medicines have been found to be ineffective. The drug works within the tissue of the patient's brain to prevent seizures from occurring.

Patients should be aware that methsuximide will not cure epilepsy. However, the drug will help to reduce the severity and number of seizures that you suffer, provided that you take the drug correctly.

Conditions treated

  • Petit mal epilepsy

Type of medicine

  • Anticonvulsant
  • Capsule

Side effects

Like most medicines, methsuximide can cause a few unwanted side effects, as well as the effects it is intended to produce. You may not suffer from any of these effects, but if they do take place, you may need to seek further medical help.

If you notice any of the effects listed below while you are using methsuximide, check with your health care professional right away:

  • Changes in vision
  • Unusual tiredness or weakness
  • Unusual bleeding or bruising
  • Unusual behavior
  • Trembling, unsteadiness, or other problems with co-ordination or muscle control
  • Trouble sleeping
  • Trouble in concentrating
  • Tiredness
  • Swollen glands
  • Swelling around the eyes
  • White spots, sores, or ulcers, in the mouth or on the lips
  • Sore throat
  • Shortness of breath
  • Unsteady walk and shakiness
  • Severe mood or mental changes
  • Red, irritated eyes
  • Red, purple-centred skin lesions
  • Pale skin
  • Painful or difficult urination
  • Nervousness
  • Lower back or side pain
  • Loss of interest or pleasure
  • Poor appetite
  • Joint or muscle pains
  • Itching
  • Irritability
  • High fever
  • Hallucinations
  • Paranoia
  • Feeling sad or empty
  • Feelings of discouragement
  • Diarrhea
  • Cough or hoarseness
  • Cloudy urine
  • Chills
  • Chest pain
  • Bloody, black, or tarry stools
  • Blood in your urine
  • Peeling, blistering, or loosening of the skin
  • Suicidal thoughts or attempts at suicide
  • Attack, assault, or force

In the event of an overdose of methsuximide, you may notice the following signs. Summon emergency medical assistance right away if you think you have taken an overdose of this drug:

  • Pale or blue lips, skin, or fingernails
  • Loss of consciousness
  • Irregular, rapid or slow, or shallow breathing
  • Difficult or troubled breathing
  • Changes in consciousness

There are some side effects that may be caused by methsuximide that resolve themselves during your treatment as your body becomes accustomed to the new medicine. In addition, your GP may be able to suggest ways of preventing these side effects or reducing their effect.

However, if any of the following effects prove to be persistent or especially bothersome, check with your health care professional:

  • Weight loss
  • Unable to sleep
  • Skin rashes
  • Reddening of the skin
  • Discomfort or pain in the chest, throat, or upper stomach
  • Nausea or vomiting
  • Loss of or very poor appetite
  • Increased sensitivity of the eyes to sunlight
  • Hives or welts
  • Repeated bouts of hiccups
  • Heartburn
  • Drowsiness
  • Dizziness
  • Poor night vision
  • Constipation
  • Change in color vision
  • Blurred vision

This is not necessarily an exclusive list. If you notice any other odd effects, you should check with your treating physician right away.


This medication should only be taken as you have been instructed to use it by your health care professional. Do not take more or less of it, take it more often, or use it for an extended course unless your health care professional has told you to change your dose.

Before taking each capsule of methsuximide, check to ensure that the contents has not melted and that the capsules are full. If this is not the case, contact your pharmacist for a refill prescription right away and return the damaged medicine. If the capsules are not in good condition, the drug will not work properly.

You can methsuximide with other seizure drugs. Be sure to continue using all your prescribed anticonvulsant medicines unless your health care professional has told you to stop.

When you collect your prescription of methsuximide, you will be issued with a patient information leaflet. Read the contents of the leaflet thoroughly and check with your health care professional if you do not understand any of the contents.

The dose of methsuximide that you will be prescribed will probably be different for different patients. You should follow your health care professional's instructions or the directions on the product label. The information contained in this guide is intended purely as a guide. Do not change your dose unless you are told to do so by a health care professional.

The dose you are prescribed will depend on how strong the medication is. In addition, your daily dose rate, the time lapse between doses, and the total duration of your course of treatment with methsuximide will be dependent on your health condition and the way in which your body responds to the drug.

For the treatment of seizures, oral capsules:

Adults, teens, and children:

Initially, take 300 mg once daily. Your health care professional may increase your dose as required.

If you forget to take a dose of this medicine, try to take it right away. However, if your next scheduled dose is almost due, omit the one you forgot and revert to your usual schedule of dosage. Do not take double doses.

Never share your prescription of methsuximide with anyone else.

If you think that your condition is getting worse or is not showing any signs of improvement, you should check with your health care professional right away. Do not stop taking methsuximide unless your doctor tells you to.


Drug interactions

There are some drugs that should never be used at the same time as methsuximide. However, in some cases, it may be appropriate for a patient to use two drugs together, even though doing so may cause an interaction to take place. While you are taking methsuximide, you must tell your health care professional if you are also using any other medicines, especially those contained in the following list.

It is not recommended that you use methsuximide with any of the following medicines as doing so could increase the risk of certain side effects. However, this may be necessary in some circumstances. If you are prescribed both drugs together, your GP may adjust the dose or frequency of use of one or both of them:

  • Phenytoin
  • Orlistat
  • Lamotrigine
  • Ginkgo
  • Fosphenytoin
  • Felbamate
  • Calcifediol

Other interactions

There are some drugs that must not be taken when you are eating certain foodstuffs. In addition, using alcohol or tobacco can cause interactions with some drugs. You should discuss this aspect of your treatment with your health care professional before you begin using methsuximide.

Medical interactions

Some historical or pre-existing medical conditions can affect how methsuximide works. Be sure to discuss your medical history with your health care professional before you start taking this medicine.

Methsuximide should be used with caution in patients with the following conditions, as this drug may make these problems worse:

  • Systemic lupus erythematosus (immune system disease)
  • Liver disease
  • Kidney disease
  • Grand mal or tonic-clonic seizures
  • History of depression
  • Bone marrow problems
  • Blood disorders

Patients should be aware that methsuximide can reduce the body's ability to fight off infection. While you are using this medication, try to avoid environments where infections such as coughs and colds may be spread.


Before you start using a medicine, you should consider the risks as well as the benefits of doing so. This decision should be arrived at following detailed discussions with your treating physician. In the case of methsuximide, you should bear in mind the points raised below.

Be sure to tell your health care professional about any allergies that you have demonstrated to methsuximide or any other prescription or over the counter medication. You should also mention if you have any known allergies to food dyes, preservatives, certain food groups, or animal by-products.

Although there have been no studies carried out that would preclude the use of methsuximide in children, you should discuss this with your child's health care professional if you have any concerns.

Although there have been no studies carried out that would preclude the use of methsuximide in geriatric patients, it is possible that elderly people are more likely to suffer from liver or kidney problems, which may mean that the dose of this drug will need adjusting.

Although there have been no studies carried out that would preclude the use of methsuximide by women who are breastfeeding, you may wish to consider using an alternative feeding solution for your child while you are using this medicine. Discuss this issue with your midwife or GP for further information and advice.

While you are using methsuximide, you should make regular visits to your health care professional for check-ups. These visits are necessary to ensure that the medication is working as anticipated and to discuss any unwanted side effects. You may also need urine and blood tests while you are taking this drug.

If you are, or if you become pregnant while you are taking methsuximide, tell your health care professional. It may be necessary for you to join a registry for pregnant women who are using seizure medication.

If your child or teenager is taking methsuximide, you should be aware that this medication can cause increased thoughts of suicide. If you suspect that your child is depressed or has thoughts of self-harming, tell your child's health care professional right away. Tell your child's doctor if they begin to have problems sleeping, if the start to feel unusually angry, restless, nervous or violent. Be sure to mention if there is any history in your family of manic-depression (bi-polar disorder) or suicidal tendencies.

You should not stop taking methsuximide without checking with your health care professional first. You may need to gradually reduce the amount of the medicine you are taking before stopping it altogether.

The following signs could indicate that you have developed a blood disorder:

  • Feeling unusually weak
  • Bruising easily
  • Nosebleeds or bleeding gums
  • Feeling nauseous
  • Swollen glands
  • Fever
  • Persistent sore throat

Check with your health care professional right away if you develop any of these symptoms.

Methsuximide can also leave you vulnerable to developing systematic lupus erythematosus. If you experience any of these signs, tell your doctor right away:

  • Skin rashes
  • Joint or muscle pain
  • Feeling unusually tired
  • Chest pains when breathing
  • Low-grade fever

You should consult your health care professional immediately if you notice any of the following signs, which could indicate an infection:

  • Unexplained weight loss
  • Persistent coughing
  • Night sweats
  • Headaches
  • Flu-like symptoms
  • High fever
  • Feeling generally unwell
  • Chills
  • Blurred or disturbed vision

Some people may feel drowsy, less alert, or dizzy while using methsuximide. If you are affected in this way, do not drive, operate machinery or take part in any activities that may be hazardous if you are not fully compos mentis.


Note that this medication can be easily melted. Methsuximide capsules should therefore be stored at room temperature and away from direct sunlight or other heat sources. Do not keep your capsules in a car where they could be exposed to high temperatures during hot weather.

Do not freeze the drug or allow the capsules to get wet.

Be sure to keep your prescription of methsuximide somewhere that it cannot be accessed by children or pets. If a pet eats any of your medicine, you should seek emergency veterinary advice right away.

Do not use any methsuximide capsules that have become out-of-date or that appear to be damaged. Do not keep any drugs that you no longer need.

Ask your pharmacist or doctor for advice on how to dispose of unwanted drugs. Do not flush the capsules down the drain or toilet. Do not throw the capsules out in the trash where they could be mistaken for candy and eaten by children or animals.


Methsuximide is an anticonvulsant medicine. This drug is used to treat and control petit mal (absence) seizures in patients who have epilepsy. This medicine is only used if other similar medicines have not been effective.

It should be understood that methsuximide will not cure your epilepsy. However, the medication is very effective in reducing the severity and number of seizures that patients may suffer, provided that the medicine is used exactly as directed by a medical professional.

There are a number of existing medical conditions that can be made worse by methsuximide. In addition, there are a number of drugs that interact with this medicine. For these reasons, you should discuss your medical history fully with your health care professional before you begin using methsuximide.

During the course of your treatment with the medicine, you will need to attend your doctor regularly for check-ups, which may include urine and blood tests. These visits are important as they are used to discuss any side effects that you may have experienced. In addition, your doctor will want to make sure that the drug is having the desired effects on your condition.