Chloroquine phosphate is a well-established medication with a primary indication for the prophylaxis and treatment of malaria caused by 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 actions, chloroquine possesses 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 critical processes like parasite heme detoxification and antigen presentation in immune cells.

Features

• Active Ingredient: Chloroquine phosphate
• Drug Class: 4-Aminoqunoline antimalarial/antirheumatic
• 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, long half-life (approximately 20-60 days)
• Mechanism of Action: Elevates vesicular pH, inhibiting parasite heme polymerase and altering immune cell antigen processing

Benefits

• Provides effective prophylaxis and treatment for malaria in regions with chloroquine-sensitive parasites
• Reduces symptoms and disease progression in autoimmune disorders like rheumatoid arthritis and lupus erythematosus
• Offers a well-understood safety profile with decades of clinical use and monitoring
• Demonstrates a long half-life, allowing for convenient weekly dosing in malaria prophylaxis
• Possesses both causal prophylactic and suppressive activity against the erythrocytic stages of malaria
• May exhibit antiviral properties in certain contexts, though this is not a primary indication

Common use

Chloroquine is primarily indicated for the prophylaxis and treatment of acute attacks of malaria due to Plasmodium vivax, P. malariae, P. ovale, and susceptible strains of P. falciparum. It is also used in the treatment of extraintestinal amebiasis. In rheumatology, chloroquine is prescribed for the management of discoid and systemic lupus erythematosus, and rheumatoid arthritis, particularly when conventional treatments have proven inadequate or poorly tolerated. The medication works by accumulating in parasitized erythrocytes and preventing the polymerization of toxic heme products in malaria, while in autoimmune conditions, it modulates immune responses through interference with antigen presentation and toll-like receptor signaling.

Dosage and direction

Malaria Prophylaxis (Adults): 500 mg chloroquine phosphate (300 mg base) orally once weekly, starting 1-2 weeks before exposure and continuing for 4 weeks after leaving endemic area.

Acute Malaria Treatment (Adults): Initial dose of 1 g chloroquine phosphate (600 mg base) followed by 500 mg (300 mg base) at 6, 24, and 48 hours after initial dose.

Rheumatoid Arthritis (Adults): 250-500 mg chloroquine phosphate daily, often administered with meals to minimize gastrointestinal discomfort.

Dosage must be adjusted for children based on body weight and should always be determined by a healthcare provider. Patients should be instructed to take the medication with a full glass of water and avoid crushing or chewing tablets.

Precautions

Regular ophthalmologic examinations (including visual acuity, slit lamp, funduscopic, and visual field testing) are mandatory before and during long-term therapy due to risk of irreversible retinopathy. Use with caution in patients with hepatic disease, severe gastrointestinal disorders, or neurological conditions. Periodic complete blood counts should be performed during prolonged therapy. Patients with psoriasis may experience exacerbation of their condition. Those with porphyria should avoid chloroquine as it may precipitate attacks.

Contraindications

Hypersensitivity to chloroquine or other 4-aminoquinoline compounds. Retinal or visual field changes attributable to 4-aminoquinoline compounds. Pre-existing maculopathy. Concomitant use with other drugs known to cause retinal toxicity. Not recommended in patients with known glucose-6-phosphate dehydrogenase (G6PD) deficiency due to risk of hemolysis.

Possible side effect

Common adverse reactions include headache, dizziness, nausea, vomiting, diarrhea, abdominal cramps, and pruritus. More serious side effects may include:

• Ocular: Retinopathy, corneal deposits, blurred vision, difficulty focusing
• Dermatological: Bleaching of hair, skin eruptions, photosensitivity
• Hematological: Leukopenia, thrombocytopenia, agranulocytosis
• Neurological: Neuropsychiatric changes, seizures, neuropathy
• Cardiovascular: Hypotension, electrocardiographic changes
• Musculoskeletal: Skeletal muscle weakness or neuropathy

Drug interaction

Chloroquine may potentiate the effects of digoxin and other cardiac glycosides. Concurrent use with hepatotoxic drugs may increase risk of liver damage. Antacids and kaolin may reduce absorption. May enhance the effects of hypoglycemic agents. Cimetidine may increase chloroquine levels by inhibiting metabolism. May antagonize the effects of anticonvulsants. Use with other QT-prolonging agents may increase arrhythmia risk.

Missed dose

If a dose is missed for malaria prophylaxis, take it as soon as remembered. If it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not double doses. For treatment of acute malaria, maintain the prescribed dosing schedule precisely. Contact a healthcare provider for specific guidance if multiple doses are missed.

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 with gastric lavage, activated charcoal, and aggressive supportive care including respiratory support and management of hypotension and hypokalemia. Diazepam may be administered for seizures.

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 and pets. Do not use after expiration date printed on packaging. Properly dispose of unused medication through take-back programs or according to local regulations.

Disclaimer

This information is for educational purposes only and does not constitute medical advice. Chloroquine is a prescription medication that should only be used under the supervision of a qualified healthcare professional. The prescribing physician should be consulted for diagnosis and treatment decisions. Not all uses described are approved in all jurisdictions. Resistance patterns for malaria vary by geographic region and should be considered when prescribing.

Reviews

“Chloroquine remains an essential tool in our antimalarial arsenal, particularly for non-falciparum malaria. Its weekly dosing schedule offers significant advantages for compliance in prophylaxis.” - Infectious Disease Specialist, 15 years experience

“While we’ve moved to more targeted therapies for rheumatoid arthritis, chloroquine still has a place in our treatment algorithm for select patients who cannot tolerate newer agents.” - Rheumatologist, 12 years experience

“The ocular monitoring requirements are substantial but necessary. With proper screening, we can minimize the risk of irreversible retinal damage while benefiting from its immunomodulatory effects.” - Ophthalmologist, 20 years experience

“Despite increasing resistance concerns, chloroquine continues to be valuable in specific geographic regions and for particular Plasmodium species. Its cost-effectiveness makes it accessible in resource-limited settings.” - Tropical Medicine Researcher, 18 years experience