Chloroquine phosphate is a synthetic 4-aminoquinoline antimalarial first synthesized in 1934 and introduced in the 1940s as a safer alternative to quinine. It works by killing Plasmodium parasites in red blood cells and also has anti-inflammatory effects, making it useful for autoimmune diseases like rheumatoid arthritis and lupus. Its long half-life allows weekly prophylactic use, but the emergence of resistant Plasmodium strains has limited its effectiveness in some regions.
BRAND NAMES
Common Brand Names:
Aralen: A widely recognized brand in the U.S. and internationally.
Lariago: Commonly available in India and several other countries.
Resochin: Marketed in Germany and other international regions.
Other Brand Names:
Amoquin
Arquin
Avloquin
Bitaquine
C-Quin
MECHANISM OF ACTION
Chloroquine works by interfering with the growth of Plasmodium parasites, the causative agents of malaria. It accumulates in the parasite’s food vacuole, raises its pH, and inhibits the polymerization of toxic heme, leading to parasite death. Additionally, chloroquine has anti-inflammatory and immunomodulatory properties, which makes it useful in conditions like lupus and rheumatoid arthritis.
PHARMACOKINETICS:
Absorption
Chloroquine phosphate is efficiently and almost completely absorbed from the gastrointestinal tract after oral administration, with an estimated bioavailability of approximately 75% to 90%.
Distribution
Widely distributed throughout body tissues, especially liver, spleen, lungs, kidneys, and melanin-containing tissues (retina)
It can cross the placenta and is also excreted in breast milk.
chloroquine has a strong affinity for body tissues, its terminal half-life is prolonged, typically ranging from 20 to 60 days.
Metabolism
Chloroquine is mainly metabolized in the liver by cytochrome P450 (CYP) enzymes through N-dealkylation, producing its primary active metabolites. A substantial portion of the drug is excreted unchanged in the urine. Its elimination is slow and complex, resulting in significant accumulation in body tissues.
Excretion
Chloroquine is excreted very slowly, with elimination occurring through a combination of metabolism in the liver, excretion by the kidneys, and long-term storage in body tissues.
PHARMACODYNAMICS
Chloroquine inhibits heme polymerase, resulting in the accumulation of toxic heme within Plasmodium parasites. It has a prolonged duration of action, with a half-life of 20–60 days. Patients should be informed about the potential risks of retinopathy with long-term or high-dose use, possible muscle weakness, and the risk of toxicity in children.
ADMINISTRATION
Chloroquine phosphate is administered either orally or by injection, depending on the condition being treated. The dosage and administration schedule vary significantly for different medical uses and must be directed by a doctor. Chloroquine is ineffective against chloroquine-resistant strains of malaria, which are widespread in many parts of the world.
DOSAGE AND STRENGTH
For malaria treatment (adults):
Typical initial dose: 600 mg base (1,000 mg salt)
This is followed by doses of 300 mg base (500 mg salt) administered at 6, 24, and 48 hours.
For malaria prophylaxis:
300 mg base (500 mg salt) once weekly, starting 1–2 weeks before travel and continuing 4 weeks after leaving endemic area
For autoimmune diseases:
Doses vary (e.g., 250 mg daily or as prescribed by a physician)
DRUG INTERACTIONS
When taking chloroquine phosphate, it is crucial to be aware of drug interactions that can increase toxicity, alter effectiveness, or cause severe heart problems. Serious interactions can include abnormal heart rhythms (QT prolongation), dangerously low blood sugar (hypoglycemia), and altered drug concentrations.
FOOD INTERACTIONS
Chloroquine phosphate interacts with certain foods, which can influence its absorption, effectiveness, and side effects. Taking it with food or milk is recommended to minimize gastrointestinal discomfort and enhance absorption. However, some beverages should be avoided because they may cause significant interactions.
CONTRAINDICATIONS
The primary contraindications for chloroquine phosphate are a history of retinal or visual field damage and hypersensitivity to 4-aminoquinoline compounds. While a doctor may choose to use it for treating an acute malaria attack, the potential risks and benefits must be carefully considered.
SIDE EFFECTS
Common:
Nausea, vomiting, diarrhea
Headache, dizziness
Itching or rash
Less common / serious:
Retinal toxicity (long-term use)
Cardiomyopathy or QT prolongation
Severe hypoglycaemia
Neuropsychiatric effects (e.g., agitation, hallucinations)
OVER DOSE
Symptoms: Nausea, vomiting, abdominal pain, diarrhea, dizziness, seizures, hypotension, cardiac arrhythmias, and hypokalemia.
Risk: Overdose can be life-threatening, particularly in children.
Immediate Action: Seek emergency medical attention immediately.
Treatment: Supportive care including gastric lavage, activated charcoal, intravenous fluids, cardiac monitoring, and correction of electrolyte imbalances.
TOXICITY
Chloroquine phosphate can lead to severe, potentially life-threatening toxicity, especially in overdose situations, because of its narrow therapeutic window. Acute toxicity mainly affects the cardiovascular system, while long-term use carries a risk of irreversible vision damage.
