What is the recommended dosage and administration of chloroquine (chloroquine phosphate) for the treatment of Plasmodium malariae?

Chloroquine Dosage for Plasmodium malariae Treatment

For uncomplicated Plasmodium malariae infection in chloroquine-sensitive areas, administer a total dose of 25 mg/kg chloroquine base over 3 days: adults receive 600 mg base initially, followed by 600 mg at 24 hours, and 300 mg at 48 hours; children receive 10 mg/kg, 10 mg/kg, and 5 mg/kg at 0,24, and 48 hours respectively. 1, 2

Adult Dosing

• Initial dose: 1,000 mg chloroquine phosphate salt (equivalent to 600 mg base) at hour 0 2
• Second dose: 500 mg salt (300 mg base) at 24 hours after the first dose 1
• Third dose: 500 mg salt (300 mg base) at 48 hours after the first dose 1
• Total cumulative dose: 2,500 mg salt (1,500 mg base) over 3 days 2

This represents approximately 25 mg/kg body weight for an average adult 1.

Pediatric Dosing

• First dose: 10 mg base/kg body weight at hour 0 1, 2
• Second dose: 5 mg base/kg at 6 hours after the first dose 2
• Third dose: 5 mg base/kg at 24 hours after the first dose 1, 2
• Fourth dose: 5 mg base/kg at 36 hours after the first dose 2
• Total cumulative dose: 25 mg base/kg over 3 days 1

Critical caveat: The pediatric dose should never exceed the adult dose regardless of the child's weight 2.

Administration Considerations

Supervised vs. Unsupervised Therapy

• Ideal scenario: All three doses should be administered under direct supervision over the 3-day period 1
• When supervision is not feasible: Give the first dose under supervision, then provide remaining doses to the patient with clear instructions 1

Monitoring and Follow-up

• If laboratory confirmation is performed: Administer the first chloroquine dose when the blood smear is obtained, instruct the patient to return on day 2 for results 1
• If parasitemia persists beyond 3 days: Obtain a repeat thick blood smear; if parasitemia has not decreased markedly, institute alternative therapy 1
• Reassessment timing: Patients remaining symptomatic after 48-72 hours should be evaluated for treatment failure and considered for second-line agents 1

Special Populations

Pregnant Women

• Treat aggressively using the standard adult regimen 1
• Chloroquine is safe during pregnancy and should not be withheld 1

Areas with Chloroquine Resistance

While P. malariae has historically been considered universally chloroquine-sensitive, documented chloroquine-resistant P. malariae has been reported in Indonesia 3. In such rare cases:

• Monitor treatment response closely with repeat blood smears 1
• If resistance is confirmed (persistent parasitemia with adequate chloroquine blood levels ≥100 μg/L), consider alternative antimalarials 3

Important Clinical Pitfalls

Dosing Confusion

The most common error is confusion between chloroquine phosphate (salt) and chloroquine base 2:

• 500 mg chloroquine phosphate = 300 mg chloroquine base
• Always verify which formulation you are prescribing

Pediatric Underdosing

Research suggests that the standard 25 mg/kg dose may be insufficient in younger children, particularly those under 15 years, due to differences in body surface area and drug metabolism 4. However, the current guideline-recommended dose remains 25 mg/kg until further evidence emerges 1, 2.

Misidentification of Plasmodium Species

The guidelines note that in highly endemic areas, fever is often assumed to be P. falciparum 1. However, P. malariae requires specific identification via blood smear as it has different treatment considerations and does not require primaquine for liver stage eradication (unlike P. vivax and P. ovale) 1.

Concurrent Infections

The presence of Plasmodium on blood smears does not prove malaria is the sole cause of febrile illness 1. Consider and rule out pneumonia, acute lower respiratory infection, or meningitis, particularly in children 1.