Chloroquine

Chloroquine phosphate is a well-established antimalarial agent with additional applications in the management of certain autoimmune conditions. As a 4-aminoquinoline compound, it demonstrates potent activity against erythrocytic forms of Plasmodium species while exhibiting immunomodulatory properties through lysosomal inhibition and cytokine modulation. This comprehensive profile examines chloroquine’s pharmacological characteristics, clinical applications, and safety considerations for healthcare professionals.

Features

• Chemical classification: 4-Aminoquinoline compound
• Available formulations: Oral tablets (250 mg, 500 mg chloroquine phosphate equivalent to 150 mg, 300 mg base)
• Mechanism: Inhibits hemozoin polymerization in malaria parasites; alters lysosomal pH and antigen processing in autoimmune conditions
• Bioavailability: Rapid and nearly complete gastrointestinal absorption
• Half-life: Approximately 1-2 months due to extensive tissue binding
• Metabolism: Hepatic via cytochrome P450 system
• Excretion: Primarily renal (50-70%), with enterohepatic recirculation

Benefits

• Provides rapid clinical response in acute malaria attacks through schizonticidal activity
• Offers causal prophylaxis against susceptible Plasmodium strains
• Demonstrates anti-inflammatory effects in rheumatoid arthritis and lupus erythematosus
• Shows potential antiviral activity against certain enveloped viruses
• Maintains long-lasting tissue concentrations enabling weekly dosing regimens
• Presents cost-effective treatment option in endemic regions

Common use

Chloroquine is primarily indicated for the prophylaxis and treatment of malaria caused by Plasmodium vivax, P. malariae, P. ovale, and chloroquine-sensitive P. falciparum. It remains the drug of choice for non-falciparum malaria in most regions. Additionally, chloroquine is used off-label for autoimmune conditions including rheumatoid arthritis, systemic lupus erythematosus, and discoid lupus erythematosus. Emerging research suggests potential applications in virology and oncology, though these uses remain investigational.

Dosage and direction

Malaria Prophylaxis: 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: Initial dose of 1 g chloroquine phosphate (600 mg base) followed by 500 mg (300 mg base) at 6, 24, and 48 hours. Total dose: 2.5 g chloroquine phosphate (1.5 g base) over 48 hours.

Rheumatoid Arthritis: 250-500 mg chloroquine phosphate daily, typically administered with food to minimize gastrointestinal discomfort.

Dosage adjustments required for hepatic impairment, renal insufficiency (CrCl <50 mL/min), and pediatric populations. Regular ophthalmologic monitoring recommended for patients receiving long-term therapy.

Precautions

Regular ophthalmologic examinations (visual acuity, slit lamp, funduscopy, visual field testing) every 6-12 months during long-term therapy due to risk of irreversible retinopathy. Monitor for muscle weakness, which may indicate myopathy or cardiomyopathy. Use with caution in patients with hepatic disease, alcoholism, or concomitant hepatotoxic drugs. Periodic complete blood counts recommended during prolonged therapy. May exacerbate psoriasis and porphyria. Caution advised in patients with neurological disorders or history of seizures.

Contraindications

Hypersensitivity to 4-aminoquinoline compounds. Pre-existing retinal field changes. Concurrent administration with gold therapy or phenylbutazone. History of chloroquine-associated visual field defects. Psoriasis (unless benefits outweigh risks). Porphyria. Myasthenia gravis (may exacerbate muscle weakness). Severe gastrointestinal, neurological, or blood disorders.

Possible side effect

Common (≥1%): Gastrointestinal disturbances (nausea, vomiting, diarrhea, abdominal cramps), headache, pruritus (particularly in dark-skinned individuals), visual accommodation disturbances, skin eruptions.

Serious (<1%): Retinopathy with visual field defects, corneal deposits, ototoxicity, neuromyopathy, cardiomyopathy, blood dyscrasias (agranulocytosis, aplastic anemia, thrombocytopenia), severe hypoglycemia, psychiatric disturbances (including psychosis), Stevens-Johnson syndrome.

Drug interaction

Significant interactions occur with: Digoxin (increased serum levels), Cimetidine (increased chloroquine concentrations), Ampicillin (reduced bioavailability), Cyclosporine (elevated cyclosporine levels), Antacids (reduced absorption), Mefloquine (increased seizure risk), Praziquantel (reduced praziquantel levels). May enhance effects of hypoglycemic agents. Caution with hepatotoxic drugs due to additive toxicity.

Missed dose

For malaria prophylaxis: Take missed dose as soon as remembered, then resume regular weekly schedule. Do not double dose. For acute malaria: Maintain strict dosing schedule; if vomiting occurs within 30 minutes of administration, repeat full dose. If vomiting occurs 30-60 minutes after dosing, administer half dose.

Overdose

Chloroquine overdose constitutes a medical emergency with rapid onset of symptoms including headache, drowsiness, visual disturbances, cardiovascular collapse, convulsions, and sudden respiratory arrest. Fatality may occur within hours. Treatment includes immediate gastric lavage, activated charcoal, respiratory support, and intravenous diazepam for seizures. Cardiovascular monitoring essential. Acidification of urine may enhance elimination.

Storage

Store at controlled room temperature (15-30°C/59-86°F) in tight, light-resistant containers. Keep away from moisture and excessive heat. Dispense in original container with child-resistant closure. Do not freeze. Keep out of reach of children and pets.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Healthcare professionals should consult current prescribing information and clinical guidelines. Chloroquine resistance patterns vary geographically—always verify local susceptibility before prescribing. Use during pregnancy requires careful risk-benefit assessment. Not all possible interactions, uses, or precautions are listed here.

Reviews

“Chloroquine remains invaluable for non-falciparum malaria management despite resistance concerns. Its well-characterized safety profile makes it preferable for certain patient populations when appropriate.” - Infectious Disease Specialist

“The immunomodulatory effects provide meaningful symptom control in autoimmune conditions, though ophthalmologic monitoring remains crucial for long-term users.” - Rheumatologist

“While resistance has limited its utility in many regions, chloroquine’s cost-effectiveness and safety profile maintain its importance in global malaria control programs.” - Tropical Medicine Expert