ARALEN PHOSPHATE W/ PRIMAQUINE PHOSPHATE
Clinical safety rating
avoidOther drugs that cause hemolysis or depress myeloid function can have additive effects Can cause hemolytic anemia in patients with G6PD deficiency.
Chloroquine and primaquine: Chloroquine inhibits heme polymerase in malaria parasites, preventing conversion of toxic heme to hemozoin; primaquine disrupts mitochondrial function and generates reactive oxygen species, targeting hypnozoites and gametocytes.
| Metabolism | Chloroquine: hepatic metabolism via CYP2C8 and CYP3A4; primaquine: hepatic metabolism via CYP2D6 and other enzymes. |
| Excretion | Renal: 70% (chloroquine as unchanged drug and metabolites), 20% (primaquine as metabolites); Fecal: ~10% (chloroquine); Biliary: minor for both. |
| Half-life | Chloroquine: 40-60 days (terminal); Primaquine: 6-8 hours (terminal). Clinical context: chloroquine accumulates extensively, requiring prolonged monitoring for toxicity; primaquine, shorter half-life, once-daily dosing. |
| Protein binding | Chloroquine: 50-65% bound to albumin; Primaquine: ~20% bound to albumin. |
| Volume of Distribution | Chloroquine: Vd 100-200 L/kg (extensive tissue distribution); Primaquine: Vd 3-5 L/kg (moderate distribution). Clinical meaning: large Vd of chloroquine indicates deep tissue compartments with slow release. |
| Bioavailability | Both: Oral bioavailability ~80-90% for chloroquine; ~90% for primaquine. No parenteral form for this combination. |
| Onset of Action | Oral: Antimalarial effect begins within 24-48 hours for chloroquine; primaquine radical cure effect begins after 2-3 days of therapy. |
| Duration of Action | Chloroquine: Weeks (due to accumulation); Primaquine: 24 hours per dose, but full course required (14 days) to prevent relapse. |
| Molecular Weight | Chloroquine phosphate: 515.86 Da; Primaquine phosphate: 455.34 Da |
Chloroquine phosphate 600 mg base (1 g salt) orally once daily for 2 days, then 300 mg base (500 mg salt) once daily for at least 2 weeks; plus primaquine phosphate 30 mg base orally once daily for 14 days.
| Dosage form | TABLET |
| Renal impairment | For chloroquine: GFR 10-50: 50% dose; GFR <10: 25% dose. For primaquine: No adjustment required, but monitor for hemolysis in GFR <10 due to accumulation. |
| Liver impairment | For chloroquine: Child-Pugh A/B: no adjustment; Child-Pugh C: reduce dose by 50% or avoid. For primaquine: Child-Pugh A/B: no data, use with caution; Child-Pugh C: contraindicated due to risk of hemolysis in glucose-6-phosphate dehydrogenase (G6PD) deficiency and impaired clearance. |
| Pediatric use | Chloroquine: 10 mg base/kg orally once daily for 2 days, then 5 mg base/kg once daily (max 300 mg base/day) for 2 weeks. Primaquine: 0.5 mg base/kg orally once daily for 14 days (max 30 mg base/day). Ensure G6PD screening before use. |
| Geriatric use | Use lower end of adult dose for chloroquine due to reduced renal function; adjust according to CrCl. For primaquine, monitor for G6PD deficiency and hemolysis; dose as per adult. Consider increased risk of QT prolongation with chloroquine. |
| 1st trimester | Avoid. Primaquine may cause hemolytic anemia in G6PD-deficient fetuses; chloroquine is generally considered safe in pregnancy for malaria prophylaxis, but this combination is not recommended in first trimester due to primaquine risks. |
| 2nd trimester | Avoid unless benefit outweighs risk. Both drugs cross placenta; primaquine can cause hemolysis in G6PD-deficient fetuses. Limited safety data for combination. |
| 3rd trimester | Avoid near term. Primaquine may cause hemolysis in newborn if G6PD deficient. Chloroquine safe but combination not recommended. |
Clinical note
Other drugs that cause hemolysis or depress myeloid function can have additive effects Can cause hemolytic anemia in patients with G6PD deficiency.
| FDA category | Contraindicated |
| Placental transfer | Both chloroquine and primaquine cross the placenta. Chloroquine reaches fetal plasma concentrations similar to maternal; primaquine transfer is less documented but expected. |
| Breastfeeding | Chloroquine and primaquine are excreted into breast milk in small amounts. Primaquine may cause hemolytic anemia in G6PD-deficient infants. Use with caution; monitor infant for jaundice, dark urine, or pallor. Avoid in breastfeeding if infant has G6PD deficiency. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | In first trimester, chloroquine is generally considered low risk for major malformations, but primaquine is contraindicated due to risk of hemolytic anemia in G6PD-deficient fetuses. Second and third trimesters: chloroquine is safe, but primaquine should be avoided as fetal G6PD status is unknown. |
| Fetal Monitoring | Maternal: Complete blood count (CBC), G6PD screening (prior to primaquine), liver function tests, visual acuity (chloroquine retinal toxicity). Fetal: Ultrasound for growth and development if used in first trimester; monitor for hemolysis if primaquine used near term. |
| Fertility Effects | No significant adverse effects on fertility reported for either chloroquine or primaquine. However, animal studies have shown some reproductive toxicity at high doses, but human data are lacking. |
■ FDA Black Box Warning
Primaquine may cause hemolytic anemia in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Test for G6PD deficiency before starting therapy.
| Common Effects | GI upset |
| Serious Effects |
G6PD deficiencyPregnancy (especially first trimester) unless treating acute malariaConcurrent use of hepatotoxic drugsKnown hypersensitivity to chloroquine or primaquineSevere renal impairment
| Precautions | Hemolytic anemia (especially G6PD deficiency), bone marrow suppression, prolonged QT interval, visual disturbances (retinopathy with chloroquine), methemoglobinemia, and severe hypersensitivity reactions. |
| Food/Dietary | No clinically significant food interactions reported. However, antacids containing magnesium or aluminum can reduce chloroquine absorption; separate administration by at least 4 hours. Grapefruit juice may increase chloroquine levels via CYP3A4 inhibition; avoid concurrent use. |
| Clinical Pearls | Combination of chloroquine and primaquine is used for radical cure of P. vivax and P. ovale malaria. Chloroquine is effective against blood-stage parasites; primaquine eradicates hypnozoites in the liver. Screen for G6PD deficiency before initiating primaquine to prevent hemolytic anemia. Concurrent use with hematotoxic drugs (e.g., dapsone) increases hemolysis risk. Contraindicated in G6PD-deficient patients, pregnancy, and breastfeeding unless no alternative. Monitor for QT prolongation, especially with electrolyte abnormalities or concurrent QT-prolonging agents. |
| Patient Advice | Take with food or milk to reduce gastrointestinal upset. · Complete full course regardless of symptom resolution to prevent relapse. · Avoid alcohol during treatment due to risk of disulfiram-like reaction. · Report signs of hemolysis: dark urine, jaundice, pallor, fatigue (especially if G6PD deficient). · Do not take antacids containing magnesium or aluminum within 4 hours of chloroquine as they reduce absorption. · Seek medical attention for visual disturbances, QT prolongation symptoms (palpitations, syncope), or severe GI distress. · Use effective contraception during and for 1 month after treatment due to potential fetal harm from primaquine. |
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