Mefloquine is an antimalarial drug developed in the 1970s by the U.S. military and later approved for medical use in the 1980s for the treatment and prevention of malaria. Its history is marked by strong effectiveness against chloroquine-resistant Plasmodium falciparum, making it widely used in endemic regions. However, post-marketing surveillance revealed significant neuropsychiatric adverse effects, including anxiety, depression, hallucinations, and in rare cases, long-term neurological symptoms, which led to stricter prescribing guidelines and warnings. Mefloquine, a quinoline-methanol antimalarial, remains an important option for malaria prophylaxis and treatment in selected cases, particularly where resistance limits other therapies. Its development was supported by military research programs, and its distribution has been guided by extensive safety monitoring and risk-benefit assessments.
BRAND NAMES
Lariam – the most widely recognized brand used for malaria prevention and treatment.
MECHANISM OF ACTION:
Mefloquine acts by interfering with the growth and survival of Plasmodium parasites in the human bloodstream. It is believed to concentrate within the parasite’s food vacuole, where it disrupts the detoxification of heme (a toxic byproduct of hemoglobin digestion). This leads to accumulation of toxic heme compounds, which damages parasite membranes and proteins, ultimately causing parasite death. It is primarily effective against blood-stage forms of malaria, especially Plasmodium falciparum.
PHARMACOKINETICS
Absorption
Mefloquine is well absorbed after oral administration, with bioavailability enhanced by food, especially fatty meals. Peak plasma concentrations are typically reached within 6–24 hours.
Distribution
It has a large volume of distribution due to extensive tissue uptake, particularly in the liver, lungs, and red blood cells. Plasma protein binding is high (around 98%), contributing to its long duration of action.
Metabolism
Mefloquine is extensively metabolized in the liver, mainly via the CYP3A4 enzyme system, forming inactive metabolites.
Elimination
It is eliminated slowly, primarily in feces via biliary excretion. A smaller fraction is excreted in urine. The elimination half-life is long, approximately 2–4 weeks, supporting once-weekly dosing for prophylaxis.
PHARMACODYNAMICS
Mefloquine acts as a blood schizonticide, targeting the asexual erythrocytic stage of malaria parasites. It disrupts heme detoxification within the parasite’s digestive vacuole, leading to toxic accumulation and parasite death. It is effective against chloroquine-resistant strains of Plasmodium falciparum. However, its action does not target liver-stage hypnozoites, so it is not effective for preventing relapse in P. vivax or P. ovale infections.
ADMINISTRATION
Mefloquine is administered orally in tablet form. It is used both for malaria prophylaxis (once weekly dosing) and treatment of acute malaria (higher initial dosing followed by additional doses). It should be taken with food and a full glass of water to improve absorption and reduce gastrointestinal irritation. It is usually started 1–2 weeks before travel for prophylaxis in malaria-endemic regions.
DOSAGE AND STRENGTH
For malaria prevention in adults, the typical dose is 250 mg once weekly. For treatment of acute uncomplicated malaria, dosing is weight-based, commonly split into two or three doses totaling approximately 20–25 mg/kg. Pediatric dosing is also weight-based, with adjustments according to body weight. Dosage should always follow regional treatment guidelines due to resistance patterns.
DRUG INTERACTIONS
Mefloquine interacts with drugs that affect cardiac conduction or CNS function. Concomitant use with other drugs that prolong the QT interval or with anticonvulsants, antidepressants, or antipsychotics may increase risk of neuropsychiatric or cardiac adverse effects. CYP3A4 inducers or inhibitors may also alter drug levels.
FOOD INTERACTIONS
Food, especially fatty meals, increases absorption of mefloquine and may enhance tolerability. It is recommended to take the drug with food to reduce gastrointestinal side effects such as nausea.
CONTRAINDICATIONS
Mefloquine is contraindicated in patients with a history of major psychiatric disorders (such as depression, psychosis, or seizures). It is also contraindicated in individuals with known hypersensitivity to the drug or related compounds.
SIDE EFFECTS
Common side effects include nausea, vomiting, dizziness, abdominal pain, headache, and vivid dreams. Neuropsychiatric effects such as anxiety, depression, insomnia, hallucinations, and mood changes may occur and can be severe in some patients. Rarely, seizures and cardiac conduction abnormalities may occur.
OVER DOSAGE
Overdose of Mefloquine is uncommon but can lead to significant toxicity, primarily affecting the central nervous system and cardiovascular system. Acute overdose symptoms may include severe dizziness, nausea, vomiting, abdominal pain, confusion, and visual disturbances.
TOXICITY
Toxicity of Mefloquine is primarily neuropsychiatric in nature, with symptoms including severe anxiety, psychosis, hallucinations, and long-lasting neurological effects in rare cases. Cardiovascular toxicity (such as arrhythmias) is uncommon but possible. Overdose may intensify CNS effects such as confusion, dizziness, and seizures. There is no specific antidote; treatment is supportive.
