Methsuximide belongs to the class of medications called anticonvulsants. It is used for the management of certain types of seizures (absence or petit mal seizures) that have not responded to other medications. It works in the central nervous system (the brain) to control seizures.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended dose of methsuximide should be the least amount needed to control seizures without causing side effects. The recommended starting dose is 300 mg daily for the first week. The doctor may then increase the dose on a weekly basis according to need. The eventual dose usually ranges from 300 mg daily to 1,200 mg daily. Methsuximide may be taken with or without food.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not take this medication if you:

• are allergic to methsuximide or any ingredients of this medication
• are allergic to any other succinimides (such as ethosuximide)

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• clumsiness or unsteadiness
• diarrhea
• dizziness
• drowsiness
• headache
• hiccups
• irritability
• loss of appetite
• nausea or vomiting
• stomach cramps
• weight loss

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• abdominal pain
• aggressiveness
• difficulty moving or controlling movements
• hallucinations
• nightmares
• pain or inflammation of the joints
• shortness of breath
• skin rash and itching
• signs of bleeding (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• signs of depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
• signs of infection (symptoms may include fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• unusual tiredness or weakness

Stop taking the medication and seek immediate medical attention if any of the following occur:

• seizures
• suicidal thoughts or behaviour
• symptoms of a serious allergic reaction (such as fever, swollen glands, yellowing of skin or eyes, or flu-like symptoms with skin rash or blistering)
• symptoms of a serious skin reaction (such as skin rash; red skin; blistering of the lips, eyes, or mouth; skin peeling; fever; or joint pain)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.

Behaviour problems: Methsuximide can cause behaviour and mood problems such as agitation, anxiety, nervousness, depression, hostility, and mood swings in people with or without a history of having these problems. Talk to your doctor as soon as possible if you experience these feelings or behaviours.

Blood disorders: Blood disorders, although infrequent, may be serious and have been reported to be associated with the use of methsuximide. Your doctor will probably recommend that you have blood tests while taking this medication.

Drowsiness/reduced alertness: Methsuximide may impair the mental or physical abilities required for potentially hazardous tasks such as driving or operating machinery. Before undertaking such activities, determine how this medication affects you.

Lupus: Cases of systemic lupus erythematosus have been reported with the use of this medication.

Kidney or liver disease: If you have liver or kidney disease you should be very closely monitored by your doctor while taking methsuximide.

Stopping medication: Do not stop taking this medication suddenly. If you need to stop taking the medication, decrease the dosage slowly as directed by your doctor.

Suicidal thoughts and behaviour: Occasionally, people taking this medication may experience thoughts of suicide. If you experience these symptoms or any other behaviour change while taking this medication, contact your doctor immediately. Family members or caregivers of people who are taking this medication should contact the person's doctor immediately if they notice unusual behaviour changes.

Pregnancy: Consult your doctor as soon as possible if you become pregnant while taking this medication. If you take methsuximide to prevent major seizures, do not stop taking it if you become pregnant. If you are taking this medication to prevent minor seizures, talk to your doctor about the risks and benefits of stopping the medication during pregnancy.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking methsuximide, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

There may be an interaction between methsuximide and any of the following:

alcohol antihistamines (e.g,. cetirizine, doxylamine, diphenhydramine, hydroxyzine, loratadine) antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone) aripiprazole azelastine azole antifungals (e.g., fluconazole, ketoconazole, voriconazole) baclofen barbiturates (e.g., butalbital, phenobarbital) benzodiazepines (e.g., alprazolam, diazepam, lorazepam) bortezomib brimonidine buprenorphine buspirone carbamazepine clonidine dabrafenib droperidol entacapone gabapentin gemfibrozil HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delaviridine, efavirenz, etravirine, nevirapine) isoniazid ketorolac lamotrigine levetiracetam

magnesium sulfate mefloquine methotrimeprazine metyrosine mirtazapine moclobemide muscle relaxants (e.g., cyclobenzaprine, methocarbamol, orphenadrine) narcotic pain relievers (e.g., codeine, fentanyl, morphine, oxycodone) olopatadine paraldehyde perampanel phenytoin pramipexole pregabalin primidone rifampin ropinirole scopolamine selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, duloxetine, fluoxetine, paroxetine, sertraline) sodium oxybate tapentadol ticlopidine topiramate tramadol zolpidem zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.