Mefloquine belongs to the class of medications called antimalarials. Mefloquine is used to treat and prevent malaria infections caused by certain types of parasites.

Malaria is an infection caused by a group of parasites called Plasmodia that enter the blood through bites from infected mosquitoes. The parasites first enter and destroy red blood cells, then they reproduce within the liver and are released into the blood. Mefloquine does not prevent the mosquitoes from biting or prevent the parasite from reproducing in the liver. Mefloquine works by destroying the parasite after it is released from the liver into the blood.

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 preventative dose of mefloquine is 250 mg once a week. This medication should be taken on the same day of the week for the following time period:

• one week before arrival in a malaria area (to allow blood levels of the medication to be effective)
• throughout your stay in this area
• 4 weeks after leaving the area (in case you have been infected and the parasite is reproducing in the liver)

For people who weigh less than 45 kg (99 lbs), your doctor will adjust the dose of mefloquine according to your body weight.

Your doctor may recommend starting this medication 2 weeks before you travel to a malaria area in order to determine how this medication affects you and if you will be able to tolerate it.

The dose of mefloquine for treatment of malaria is based on body weight (20 mg/kg to 25 mg/kg for those with no immunity, and 15 mg/kg for those with partial immunity). The total dose is taken all at once or in 2 to 3 doses spaced 6 or 8 hours apart to reduce the occurrence or severity of side effects. If a person vomits less than 30 minutes after receiving the medication, a full additional dose should be taken as instructed by your doctor. If vomiting occurs 30 to 60 minutes after the dose, an additional one-half dose should be taken as instructed by your doctor.

Many things can affect the dose of a 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.

Mefloquine should be taken with food (e.g., any meal) and with plenty of water (at least 240 mL, equivalent of 1 cup [8 ounces]). Do not chew the tablets, but you may crush and mix them with a small amount of water, milk, or other beverage.

It is very important to take this medication exactly as prescribed by your doctor. Do not take a double dose. For missed doses intended for prevention of malaria, take the dose as soon as you remember and take each remaining dose according to the weekly dosing schedule, counting from the day you took the missed dose. Do not take more than one dose in a week.

Immediately contact a doctor if you suspect that you have contracted malaria. Your doctor may recommend a self-treatment plan if you cannot get to a doctor within 12 to 24 hours.

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

Each white, round, biconvex tablet, cross scored on one side, and plain on the other side, contains 250 mg of mefloquine (base) as mefloquine hydrochloride. Nonmedicinal ingredients: microcrystalline cellulose, magnesium stearate, croscarmellose sodium, and colloidal silicon dioxide.

Do not take this medication if you:

• are allergic to mefloquine or any ingredients of the medication
• are allergic to related medications (e.g., quinine, quinidine, chloroquine)
• are taking any of the following medications:
• quinine
• quinidine
• chloroquine
• ketoconazole
• halofantrine
• have a history of psychiatric disturbances (including depression, generalized anxiety disorder, schizophrenia, or other major psychiatric disorders)
• have a history of suicide attempt or self-harming thoughts or behaviour
• have a history of seizures

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.

• abdominal pain
• abnormal dreams
• diarrhea
• dizziness
• fatigue
• headache
• loss of appetite
• loss of balance
• nausea
• spinning sensation
• trouble sleeping
• vomiting

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do seek medical attention.

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

• chills
• fever
• irregular heartbeat or palpitations
• irritability
• mood or mental changes (e.g., anxiety, paranoia, hallucinations, confusion, panic attacks)
• muscle aches or pain
• prickling or tingling sensation
• numbness and loss of ability to feel pain or temperature change, especially in the feet
• burning or sharp pain in feet
• loss of coordination or balance
• pain caused by a light touch
• restlessness
• ringing in the ears
• severe or continuing headache
• signs of depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
• 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)
• signs of inflammation of the lungs (e.g., fever, chills, shortness of breath, cough)
• skin rash
• unusual tiredness or weakness

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

• seizures
• severe muscle weakness or paralysis
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort
• thoughts of self-harm or suicide

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 using 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 use this medication.

Anemia: Mefloquine may cause low levels of red blood cells. If you experience symptoms of reduced red blood cell count (anemia) such as shortness of breath, feeling unusually tired or pale skin, contact your doctor as soon as possible.

Dizziness/reduced alertness: Dizziness, a disturbed sense of balance, and other problems with the nervous system have been reported during and after the use of mefloquine. In some cases, these side effects have become permanent. Use caution when performing tasks requiring mental alertness and coordination (such as driving or operating machinery).

Drug interactions: Taking mefloquine at the same time as other medications, including quinine, quinidine, and chloroquine, may cause heart rhythm problems, cardiac arrest, or increase the risk of seizures. Do not take these medications at the same time as mefloquine. Halofantrine and ketoconazole may affect the electrical activity of the heart and cause QT prolongation. Do not take halofantrine or ketoconazole while taking mefloquine for the prevention or treatment of malaria, or for 15 weeks after the last dose of mefloquine.

Heart conditions: Mefloquine can cause heart rhythm problems. If you develop an abnormal or irregular heartbeat or palpitations while taking mefloquine to prevent malaria, contact a doctor as soon as possible. If you have heart rhythm problems, you should discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver disease: People with liver disease may experience higher blood levels of this medication. If you have liver disease, talk to your doctor about the benefits and risks of using this medication.

Mental problems: Some people taking mefloquine may experience psychiatric symptoms (including depression, generalized anxiety disorder, paranoia, hallucinations, and psychotic behaviour). In rare cases, they may have thoughts of suicide. If you have a history of psychiatric disturbances (including depression, generalized anxiety disorder, schizophrenia, or other major psychiatric disorders), you should not take this medication.

If you are taking mefloquine to prevent malaria and you experience a sudden onset of anxiety, depression, thoughts of self-harm or suicide, restlessness or irritability, or confusion (which are possible signs of more serious mental problems), contact a doctor or health care provider as soon as possible. You may need to stop taking mefloquine and use another malaria prevention medication instead.

Nervous System Problems: Some people taking mefloquine may experience serious nervous system problems. If you experience dizziness, vertigo or a spinning sensation, loss of balance, ringing in your ears, difficulty sleeping, or seizures, contact your doctor immediately.  These side effects may occur at any time while you are taking mefloquine and in some cases have lasted for months or years after stopping mefloquine.  In some people side effects of dizziness, vertigo, loss of balance and ringing in the ears have become permanent.

Seizure disorder: Mefloquine may increase the risk of seizures in people who have epilepsy. People with a history of seizures should not take mefloquine to prevent malaria, and should only take mefloquine to treat malaria if the benefits outweigh the risks.

Stopping the medication: If you are told by a doctor or other health care provider that you need to stop taking mefloquine because of side effects or other reasons, you will need to take another malaria prevention medication. Leave the malaria area if you cannot get another medication. However, leaving the malaria area may not protect you from getting malaria; you still need to take a malaria prevention medication.

Pregnancy: If possible, it is best if pregnant women avoid travelling to areas where they risk malaria exposure. This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately. Women of childbearing age should use reliable birth control while taking mefloquine and for 3 months after the last dose has been taken.

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

Children: The safety and effectiveness of using this medication have not been established for children less than 3 months old or weighing less than 5 kg.

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

• acetazolamide
• alcohol
• amiodarone
• antihistamines (e.g., cetirizine, chlorpheniramine, dimenhydrinate, diphenhydramine, loratadine)
• other anti-malarial medications (e.g., hydroxychloroquine, primaquine)
• anti-psychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• "azole" antifungals (e.g., itraconazole, ketoconazole, voriconazole)
• beta-blockers (e.g., atenolol, metoprolol, sotalol)
• bosentan
• cobicistat
• conivaptan
• dapsone
• disopyramide
• dronedarone
• enzalutamide
• flecainide
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., efavirenz, etravirine, nevirapine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• methadone
• mifepristone
• mitotane
• modafinil
• pregabalin
• procainamide
• quinidine
• quinine
• quinolone antibiotics (e.g., ciprofloxacin, norfloxacin)
• rifabutin
• rifampin
• St. John's wort
• seizure medications (e.g., carbamazepine, gabapentin, levetiracetam, phenobarbital, phenytoin, topiramate)
• selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline)
• serotonin antagonists (anti-emetic medications; e.g., granisetron, ondansetron)
• siltuximab
• tricyclic antidepressants (e.g., amitriptyline, imipramine, nortriptyline)
• tyrosine kinase inhibitors (e.g., lapatinib, pazopanib, sunitinib)
• warfarin

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 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.