Medication Overview

Chloroquine is an antimalarial medication used primarily to prevent and treat malaria caused by sensitive Plasmodium species. It is also utilized in the treatment of certain autoimmune conditions like rheumatoid arthritis and lupus erythematosus. Chloroquine functions by interfering with the growth of parasites in the red blood cells of the human body.

Therapeutic Indications

Chloroquine is indicated for the treatment and prevention of acute attacks of malaria due to susceptible strains of Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale, and Plasmodium vivax. Additionally, it is prescribed for the treatment and management of autoimmune diseases like rheumatoid arthritis and systemic lupus erythematosus. It is occasionally utilized in off-label applications for amebiasis.

Pharmacokinetics

Chloroquine is well absorbed from the gastrointestinal tract, with peak plasma concentrations occurring within 1 to 2 hours after oral dosing. The drug exhibits extensive tissue distribution and accumulates in the liver, spleen, kidney, and lungs. Chloroquine is metabolized predominantly in the liver to active metabolites and has a long elimination half-life, facilitating once-weekly dosing in malaria prophylaxis.

Mechanism of Action

Chloroquine primarily functions by interfering with the parasite’s ability to sequester heme, a toxic byproduct of hemoglobin degradation. This disruption leads to the accumulation of toxic compounds within the parasite and its eventual death. In autoimmune conditions, its exact mechanism is not fully understood but it is postulated to inhibit neutrophil and eosinophil function, and impede the release of superoxide by neutrophils.

Dosage and Administration

For malaria prophylaxis, the typical adult dosage is 500 mg chloroquine phosphate (300 mg base) taken once a week on the same day each week. Treatment dosages for acute malaria attacks vary depending on the Plasmodium species and subject response, with initial higher doses followed by subsequent reductions. In autoimmune diseases, the dosage regimen is generally lower but requires consistent monitoring. Dosage adjustments may be necessary based on patient response and tolerance.

Drug Interactions

Chloroquine may interact with other medications, potentially altering their effects. Concurrent administration with cimetidine can increase chloroquine levels and the risk of toxicity. The drug may also reduce the bioavailability of ampicillin. Combining chloroquine with mefloquine could increase the risk of seizures and cardiac arrest. Co-administration with antacids may reduce chloroquine absorption, necessitating time separation between these medications.

Adverse Reactions

Common adverse effects include gastrointestinal disturbances, such as nausea, vomiting, and cramping. Central nervous system manifestations like headache, dizziness, and insomnia are also prevalent. Notably, long-term administration can result in more serious toxicities, including retinopathy, which necessitates regular eye exams, and cardiomyopathy. Hematologic abnormalities such as aplastic anemia and leukopenia may occur, especially in prolonged use.

Special Populations

Special caution is advised when prescribing chloroquine to pregnant or lactating women due to the lack of conclusive safety data. In pediatric populations, the dosage should be carefully calculated based on weight to avoid overdose, which can be fatal. Elderly patients may require dosage adjustments due to the increased likelihood of hepatic, kidney, or cardiac functionality impairments. Routine screening and monitoring may be required in these groups.

Laboratory Tests Monitoring

Regular blood counts are advised to detect potential hematologic abnormalities early. Liver function tests should be conducted to monitor hepatic enzyme levels, given the risk of hepatotoxicity. Baseline and periodic ophthalmologic exams are crucial to identify any retinopathy or visual field defects, especially for those on long-term chloroquine therapy. ECG monitoring may be warranted in patients with cardiac conditions or those receiving high doses.

Contraindications

Chloroquine is contraindicated in individuals with known hypersensitivity to chloroquine or 4-aminoquinoline compounds. Patients with preexisting retinal or visual field changes attributed to 4-aminoquinoline compounds should avoid this medication. The drug is also contraindicated in patients with a history of epilepsy or other seizure disorders due to the potential exacerbation of these conditions.

Pharmaceutical Forms

Chloroquine is available in multiple forms, including oral tablets and injections. Tablets are the most common form, typically prescribed for both prophylaxis and treatment of malaria, as well as for autoimmune conditions. Injectable forms are generally reserved for severe cases of malaria where patients are unable to tolerate oral medications.

Storage and Handling

Chloroquine tablets should be stored at room temperature, away from light and moisture. The drug must be kept out of reach of children due to the risk of accidental overdose, which can be fatal. For injectable forms, specific storage instructions provided by the manufacturer should be closely followed. Proper disposal of unused or expired medication is recommended to prevent environmental contamination.