Chloroquine phosphate is a well-established medication primarily indicated for the prophylaxis and treatment of acute attacks of malaria due to susceptible strains of Plasmodium species. It belongs to the 4-aminoquinoline class of compounds and has been a cornerstone of antimalarial therapy for decades. Beyond its antiparasitic applications, chloroquine exhibits significant immunomodulatory properties, leading to its use in the management of certain autoimmune conditions such as rheumatoid arthritis and lupus erythematosus. Its mechanism of action involves raising the pH within intracellular vesicles, which interferes with the replication of parasites and the antigen-processing pathways in immune cells. This profile provides a comprehensive, evidence-based overview of chloroquine for healthcare professionals.

Features

• Active Ingredient: Chloroquine phosphate
• Chemical Class: 4-Aminoquinoline
• Available Forms: Oral tablets (250 mg, 500 mg chloroquine phosphate, equivalent to 150 mg and 300 mg base, respectively)
• Pharmacokinetics: Well-absorbed orally, extensive tissue distribution, metabolized in the liver, eliminated slowly via kidneys
• Half-life: Approximately 20–60 days
• Prescription Status: Prescription-only medication

Benefits

• Provides effective chemoprophylaxis and treatment for malaria in regions with chloroquine-sensitive parasites
• Reduces symptoms and frequency of flares in autoimmune disorders like rheumatoid arthritis and lupus erythematosus
• Offers a well-understood safety profile with decades of clinical use and monitoring
• Demonstrates cost-effectiveness and wide availability in many endemic regions
• Possesses a long half-life, allowing for convenient weekly dosing in prophylaxis regimens
• Exhibits additional antiviral properties under investigational use for certain viral infections

Common use

Chloroquine is primarily used for the prevention and treatment of malaria caused by Plasmodium vivax, P. ovale, P. malariae, and some strains of P. falciparum (though resistance is widespread). In non-malarial indications, it is employed as a disease-modifying antirheumatic drug (DMARD) for rheumatoid arthritis and discoid or systemic lupus erythematosus. Off-label uses have included treatment for amoebic liver abscess and investigational applications in virology and oncology, though these are not standard indications.

Dosage and direction

Dosage must be individualized based on indication, patient weight, and renal/hepatic function. For malaria prophylaxis in adults: 500 mg chloroquine phosphate (300 mg base) orally once per week, starting 1–2 weeks before travel and continuing for 4 weeks after leaving the endemic area. For acute malaria treatment: initial dose of 1 g (600 mg base), followed by 500 mg (300 mg base) at 6, 24, and 48 hours. For rheumatoid arthritis: initial dose of 250–500 mg daily, reduced for maintenance. Always administer with food or milk to minimize gastrointestinal upset.

Precautions

Regular ophthalmologic examinations are mandatory due to risk of irreversible retinopathy with long-term use. Use with caution in patients with hepatic disease, alcoholism, or concomitant hepatotoxic drugs. Periodic complete blood counts should be performed during prolonged therapy. May exacerbate psoriasis or porphyria. Caution advised in patients with neurological disorders or history of epilepsy. Not recommended during pregnancy unless potential benefit justifies potential risk to the fetus.

Contraindications

Hypersensitivity to chloroquine or other 4-aminoquinolines. Retinal or visual field changes attributable to 4-aminoquinolines. Pre-existing maculopathy. Concurrent use with other drugs known to cause retinal toxicity. Not recommended in regions with known chloroquine-resistant P. falciparum.

Possible side effect

Common: nausea, vomiting, diarrhea, abdominal cramps, headache, dizziness, pruritus. Less common: skin eruptions, bleaching of hair, alopecia, neuromyopathy, ECG changes (including QT prolongation). Rare but serious: irreversible retinopathy, cardiomyopathy, blood dyscrasias (aplastic anemia, agranulocytosis, thrombocytopenia), seizures, psychiatric disturbances (including psychosis), hypoglycemia.

Drug interaction

Significant interactions occur with: digoxin (increased levels), cyclosporine (increased levels), cimetidine (inhibits metabolism), ampicillin (reduced bioavailability), antacids (reduced absorption). May enhance effects of hypoglycemic agents. Concurrent use with other QT-prolonging agents increases arrhythmia risk. Avoid with hepatotoxic drugs or myelosuppressive agents.

Missed dose

If a weekly prophylactic dose is missed, take it as soon as remembered, then resume the regular weekly schedule. Do not double the dose. For daily regimens, take the missed dose as soon as possible unless it is almost time for the next dose, in which case skip the missed dose and resume the regular schedule.

Overdose

Chloroquine overdose is extremely dangerous and can be fatal within hours. Symptoms include headache, drowsiness, visual disturbances, cardiovascular collapse, convulsions, and sudden respiratory and cardiac arrest. Management requires immediate medical attention, gastric lavage, activated charcoal, and intensive supportive care including respiratory and cardiovascular support. Diazepam may reduce cardiotoxicity.

Storage

Store at controlled room temperature (20–25°C or 68–77°F) in a tight, light-resistant container. Keep out of reach of children. Do not use after expiration date.

Disclaimer

This information is for educational purposes and does not replace professional medical advice. Diagnosis and treatment should be made by a qualified healthcare provider based on individual patient circumstances. Always follow local prescribing guidelines and check for updated resistance patterns in malaria-endemic regions.

Reviews

“Chloroquine remains an essential tool in our antimalarial arsenal, particularly for P. vivax infections. Its weekly dosing schedule supports adherence in prophylaxis.” – Infectious Disease Specialist, 15 years experience.

“While effective for autoimmune conditions, the ophthalmologic monitoring requirements present practical challenges in long-term management.” – Rheumatologist, 10 years experience.

“Historical significance cannot be overstated, though resistance has limited its utility in many falciparum-endemic areas. Still valuable when susceptibility confirmed.” – Tropical Medicine Physician, 20 years experience.