Chloroquine phosphate is a well-established antimalarial agent with a proven history of clinical efficacy spanning decades. As a 4-aminoquinoline compound, it demonstrates potent activity against erythrocytic forms of Plasmodium species, particularly P. vivax, P. ovale, P. malariae, and sensitive strains of P. falciparum. Beyond its antimalarial indications, chloroquine exhibits immunomodulatory properties that have led to its use in certain autoimmune conditions, though such applications require careful specialist supervision. This medication remains a cornerstone in specific prophylactic and therapeutic protocols where local resistance patterns permit its use.

Features

• Chemical classification: 4-Aminoquinoline compound
• Available formulations: Oral tablets (250mg, 500mg chloroquine phosphate equivalent to 150mg, 300mg base)
• Mechanism: Concentrates in parasitic acid vesicles, raising pH and inhibiting hemoglobin proteolysis
• Half-life: Approximately 1-2 months due to extensive tissue binding
• Metabolism: Hepatic via cytochrome P450 enzymes
• Excretion: Primarily renal (50-70%), with partial enterohepatic recirculation

Benefits

• Provides rapid clinical improvement in acute malaria attacks when caused by sensitive parasites
• Offers convenient once-weekly dosing for malaria prophylaxis in appropriate regions
• Demonstrates activity against extraerythrocytic forms of P. vivax and P. ovale, reducing relapse potential
• Exhibits anti-inflammatory effects beneficial in certain rheumatological conditions
• Presents well-established safety profile with decades of clinical use
• Maintains cost-effectiveness in resource-limited settings where appropriate

Common use

Chloroquine is primarily indicated for the prophylaxis and treatment of malaria caused by susceptible strains of Plasmodium. It remains particularly valuable for P. vivax, P. ovale, P. malariae, and chloroquine-sensitive P. falciparum infections. In rheumatology, it finds application in the management of rheumatoid arthritis and lupus erythematosus, though hydroxychloroquine is generally preferred due to its improved safety profile. Off-label uses have included treatment for certain parasitic infections like extraintestinal amoebiasis, though evidence supporting these applications varies.

Dosage and direction

Malaria prophylaxis: Adults: 500mg chloroquine phosphate (300mg base) orally once weekly, beginning 1-2 weeks before exposure and continuing for 4 weeks after leaving endemic area. Children: 8.3mg/kg chloroquine phosphate (5mg/kg base) weekly, not to exceed adult dose.

Acute malaria treatment: Adults: Initial dose of 1g chloroquine phosphate (600mg base), followed by 500mg (300mg base) at 6, 24, and 48 hours. Total dose: 2.5g chloroquine phosphate (1.5g base) over 48 hours. Children: 10mg/kg base initially, then 5mg/kg base at 6, 24, and 48 hours.

Take with food or milk to minimize gastrointestinal discomfort. Do not crush or chew tablets; swallow whole.

Precautions

Regular ophthalmological examinations are mandatory during prolonged therapy due to risk of irreversible retinopathy. Baseline and periodic CBC, liver function tests, and glucose-6-phosphate dehydrogenase (G6PD) levels should be monitored. Use with extreme caution in patients with hepatic impairment, renal insufficiency, or neurological disorders. May exacerbate psoriasis and porphyria. Caution advised in patients with history of seizure disorder or myasthenia gravis. Pregnancy Category C: Use only if potential benefit justifies potential risk to fetus.

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. In malaria prophylaxis: absolute contraindication in areas with known chloroquine-resistant P. falciparum.

Possible side effect

Common: nausea, vomiting, diarrhea, abdominal cramps, headache, dizziness, pruritus (especially in dark-skinned individuals), skin eruptions, hair loss, bleaching of hair. Ophthalmic: vortex keratopathy (corneal deposits), accommodative difficulties, retinopathy (typically after prolonged use), visual field defects, color vision disturbances. Neurological: neuropathy, neuromyopathy, seizures, extrapyramidal symptoms. Hematological: leukopenia, agranulocytosis, aplastic anemia, thrombocytopenia. Cardiac: hypotension, ECG changes (particularly T-wave inversion), conduction disorders. Rare: acute psychosis, suicidal behavior, hepatotoxicity.

Drug interaction

Significant interactions occur with: cimetidine (increases chloroquine levels), ampicillin (reduced bioavailability), cyclosporine (increased cyclosporine levels), antacids (reduce absorption - separate administration by 4 hours), mefloquine (increased seizure risk), digoxin (increased digoxin levels), insulin and oral hypoglycemics (enhanced hypoglycemic effect). Concomitant use with hepatotoxic drugs or QT-prolonging agents requires careful monitoring.

Missed dose

For prophylactic regimen: take missed dose as soon as remembered, then resume regular schedule. Do not double dose. If close to next scheduled dose, skip missed dose. For treatment regimen: contact healthcare provider immediately for guidance, as malaria treatment requires precise dosing schedule.

Overdose

Chloroquine overdose is extremely dangerous and potentially fatal, with death occurring within hours. Symptoms include headache, drowsiness, visual disturbances, cardiovascular collapse, convulsions, and hypokalemia. Cardiac manifestations include widened QRS complex, heart block, ventricular arrhythmias, and hypotension. Immediate medical attention is crucial. Treatment is supportive with emphasis on respiratory and cardiovascular support. Activated charcoal may be beneficial if given early. Acidosis should be corrected, and diazepam may reduce cardiotoxicity.

Storage

Store at controlled room temperature (15-30°C/59-86°F) in original container. Protect from light and moisture. Keep tightly closed. Do not store in bathroom or near sink. Keep out of reach of children and pets. Do not use after expiration date printed on packaging.

Disclaimer

This information is for educational purposes only and does not constitute medical advice. Chloroquine is a prescription medication that requires proper medical supervision. Healthcare providers must assess individual patient factors, including resistance patterns, comorbidities, and potential drug interactions before prescribing. Always follow the specific instructions provided by your healthcare professional and the manufacturer’s prescribing information. Self-medication with chloroquine is dangerous and inappropriate.

Reviews

“Chloroquine remains valuable in specific epidemiological contexts. Its once-weekly dosing improves compliance in prophylaxis, though resistance patterns must be carefully considered.” - Tropical Medicine Specialist, 15 years experience

“In rheumatology practice, we reserve chloroquine for specific cases where alternatives aren’t suitable. Regular retinal screening is non-negotiable for patient safety.” - Rheumatologist, 12 years experience

“The cardiac toxicity profile requires careful patient selection and monitoring, particularly in those with pre-existing conduction abnormalities.” - Cardiologist, 18 years experience