Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
FANSIDAR vs ARALEN HYDROCHLORIDE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Fansidar combines sulfadoxine, a sulfonamide dihydrofolate reductase inhibitor, and pyrimethamine, a dihydrofolate reductase inhibitor, synergistically inhibiting folate synthesis in Plasmodium species, leading to nucleic acid synthesis inhibition and parasite death.
Chloroquine, a 4-aminoquinoline, accumulates in acidic organelles such as lysosomes and food vacuoles of malaria parasites, raising p H and inhibiting hemozoin polymerization, which leads to toxic heme accumulation and parasite death. It also has anti-inflammatory and immunomodulatory effects by inhibiting TLR signaling and cytokine production.
Treatment of chloroquine-resistant Plasmodium falciparum malaria (FDA-approved),Prevention of malaria in travelers to regions with chloroquine-resistant P. falciparum (off-label)
Treatment of uncomplicated malaria due to chloroquine-sensitive Plasmodium species,Prophylaxis of malaria in areas with chloroquine-sensitive parasites,Extraintestinal amebiasis,Treatment of discoid lupus erythematosus (off-label),Treatment of rheumatoid arthritis (off-label)
For acute uncomplicated malaria: 3 tablets (25 mg pyrimethamine + 500 mg sulfadoxine per tablet) orally as a single dose on Day 0 and Day 1 (total 6 tablets); alternatively, 3 tablets as a single dose. For severe malaria: 3 tablets orally as a single dose, repeated at weekly intervals if necessary.
Chloroquine phosphate 500 mg (300 mg base) orally once weekly for prophylaxis; 600 mg base (1 g phosphate) orally initially, followed by 300 mg base (500 mg phosphate) at 6, 24, and 48 hours for treatment of malaria.
Sulfadoxine: 100-200 hours; pyrimethamine: 80-100 hours; clinical context: unusual for antimalarials, allows single-dose therapy for uncomplicated P. falciparum
48-72 hours (terminal elimination half-life); prolonged to weeks with chronic dosing due to extensive tissue accumulation, especially in the liver, spleen, and melanin-containing tissues.
Sulfadoxine is primarily metabolized by N-acetyltransferase (NAT) to N-acetylsulfadoxine; pyrimethamine is metabolized by hepatic microsomal enzymes, including CYP2C9 and CYP3A4. Both are excreted renally.
Hepatic metabolism via CYP2C8, CYP3A4, and CYP2D6 to desethylchloroquine and other metabolites.
Renal: sulfadoxine 80% (unchanged), pyrimethamine 20-40% (unchanged); fecal: sulfadoxine <5%, pyrimethamine <5%
Renal (~70% unchanged), with 10-20% in feces; biliary elimination is minor.
Sulfadoxine: 90-95% bound to albumin; pyrimethamine: 70-80% bound to albumin and globulins
50-60%, primarily to albumin and α1-acid glycoprotein.
Sulfadoxine: 1.5-2.0 L/kg (distributes widely including CSF); pyrimethamine: 2.0-3.0 L/kg (extensive tissue distribution)
50-100 L/kg; extensive tissue sequestration including erythrocytes, liver, spleen, and melanin-containing tissues like skin and retina.
Oral: sulfadoxine >85%, pyrimethamine >90%; IM: essentially 100%
Oral: ~70-80% (variable due to first-pass metabolism); intravenous: 100%.
Cr Cl 10-50 m L/min: no adjustment recommended. Cr Cl <10 m L/min: contraindicated.
Severe renal impairment (GFR <10 m L/min): reduce dose by 50% or increase dosing interval.
Child-Pugh Class A: no adjustment. Child-Pugh Class B or C: avoid use due to risk of hepatotoxicity and accumulation.
Use with caution in patients with hepatic impairment; no specific dose adjustment guidelines available; contraindicated in severe hepatic disease or porphyria.
Weight-based single dose: 5-10 kg: 1/4 tablet; 11-20 kg: 1/2 tablet; 21-30 kg: 3/4 tablet; 31-45 kg: 1 tablet; >45 kg: 2 tablets. Administer orally, repeat on Day 1 if indicated.
Prophylaxis: 5 mg base/kg orally once weekly (max 300 mg base). Treatment: 10 mg base/kg orally initially, then 5 mg base/kg at 6, 24, and 48 hours (max 600 mg base total).
No specific dose adjustment recommended, but monitor renal function closely due to age-related decline; sulfadoxine-pyrimethamine is generally well-tolerated in elderly, but caution with hepatic or renal impairment.
Start at lower end of dosing range due to increased risk of adverse effects (e.g., QT prolongation, retinal toxicity); monitor renal function.
Fatalities due to severe adverse reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias have been reported. Fansidar should not be used for malaria prophylaxis due to the risk of severe skin reactions.
No FDA black box warning.
Severe cutaneous adverse reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), hematologic toxicity (agranulocytosis, aplastic anemia), hepatic toxicity, hypersensitivity reactions, and photosensitivity. Monitor for skin reactions, blood dyscrasias, and hepatic function.
Retinopathy and irreversible retinal damage with prolonged use or high doses; requires baseline and periodic ophthalmologic exams,QT prolongation and ventricular arrhythmias, especially with concomitant QT-prolonging drugs or electrolyte abnormalities,Severe hypoglycemia including loss of consciousness,Neuropsychiatric effects including psychosis and suicidal ideation,Hemolysis in glucose-6-phosphate dehydrogenase (G6PD) deficiency
Hypersensitivity to sulfadoxine, pyrimethamine, or any sulfonamide; history of severe cutaneous adverse reactions due to sulfonamides; folate deficiency; megaloblastic anemia; infants <2 months of age (due to risk of kernicterus); pregnancy (especially first trimester) and lactation (due to risk of kernicterus and folate antagonism).
Hypersensitivity to chloroquine or any 4-aminoquinoline,Pre-existing retinopathy or known maculopathy,Known G6PD deficiency (relative, use with caution),Concomitant use with strong QT-prolonging drugs (e.g., quinidine, procainamide)
Avoid alcohol during treatment to reduce hepatotoxicity risk. High-fat meals may slightly increase pyrimethamine absorption; maintain consistent diet. Do not take with folic acid supplements as they may antagonize the drug's antifolate effect. Avoid excessive caffeine consumption; pyrimethamine may increase caffeine levels.
Avoid grapefruit and grapefruit juice as they may increase drug levels and toxicity. Limit alcohol intake to reduce risk of liver toxicity. Administer with food to decrease gastrointestinal irritation. Avoid antacids containing aluminum or magnesium; separate by at least 4 hours.
Pregnancy Category C. First trimester: Contraindicated due to sulfadoxine-pyrimethamine's antifolate activity, associated with neural tube defects and major congenital malformations (anencephaly, cleft palate) based on animal studies and human case reports. Second and third trimesters: Use only if benefit outweighs risk; no adequate human studies show fetal harm in later trimesters, but theoretical risk of kernicterus in neonate due to sulfadoxine displacement of bilirubin, especially if near term.
Chloroquine hydrochloride crosses the placenta. First trimester: associated with increased risk of spontaneous abortion and congenital abnormalities (cochleovestibular and ocular) at high doses. Second and third trimesters: possible ototoxicity and retinal toxicity; use only for malaria prophylaxis or treatment when benefit outweighs risk.
Both components are excreted into breast milk. Sulfadoxine: M/P ratio ~0.5; pyrimethamine: M/P ratio ~0.5. Concentrations in milk are low (<50% maternal plasma levels). Theoretical risk of kernicterus in jaundiced, G6PD-deficient, or ill neonates. Avoid in nursing mothers with infants at risk for hemolytic anemia. Consider alternative antimalarials during breastfeeding.
Chloroquine is excreted into breast milk in low concentrations (M/P ratio approximately 0.1-0.3). Amounts are unlikely to cause adverse effects in nursing infants. The American Academy of Pediatrics considers chloroquine compatible with breastfeeding. Monitor infant for potential ocular effects.
No dose adjustment recommended for Fansidar in pregnancy. However, pharmacokinetic changes (increased volume of distribution, reduced plasma protein binding) may slightly lower peak concentrations, but clinical efficacy is maintained. Avoid use in first trimester; if necessary in second/third trimester, use standard dose (sulfadoxine 500 mg + pyrimethamine 25 mg) as single dose for malaria treatment or weekly prophylaxis at same dose.
Increased volume of distribution and clearance during pregnancy may require higher doses for malaria prophylaxis (e.g., 400 mg base weekly) and treatment; therapeutic drug monitoring recommended for optimal dosing. No standard dose adjustment established; base dose on indication and clinical response.
Fansidar (sulfadoxine/pyrimethamine) is a fixed-dose combination antifolate used for malaria prophylaxis and treatment. Due to severe adverse reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), it is no longer recommended for prophylaxis in travelers; reserved for chloroquine-resistant Plasmodium falciparum malaria when other agents are unavailable. Administer with food to reduce GI upset. Monitor for hypersensitivity, especially in patients with sulfonamide allergy. Not effective against P. vivax or P. ovale. Consider G6PD deficiency screening before use.
ARALEN HYDROCHLORIDE (chloroquine hydrochloride) is used for malaria prophylaxis and treatment, and for amebiasis. Monitor for retinal toxicity with long-term use; baseline and periodic ophthalmologic exams recommended. Caution in patients with hepatic disease, G6PD deficiency, or porphyria. May exacerbate psoriasis and myasthenia gravis. QT prolongation possible; avoid with other QT-prolonging drugs. Administer with food to reduce GI upset. For acute malaria, dose may be divided to improve tolerance. In severe malaria, use parenteral form with cardiac monitoring.
Take with a full glass of water and with food to prevent stomach upset.,Complete the full course even if symptoms improve.,Seek immediate medical attention for rash, blisters, mouth sores, or fever—these could signal a severe skin reaction.,Avoid prolonged sun exposure and use sunscreen; photosensitivity may occur.,Inform your doctor of all medications, especially methotrexate, warfarin, or antiepileptics.,Not recommended for pregnant women or nursing mothers unless specifically advised by a physician.,Do not take if you have a sulfa allergy or history of folic acid deficiency anemia.,Store at room temperature away from moisture and heat.
Take this medication exactly as prescribed; do not skip doses for malaria prophylaxis.,If vomiting occurs within 1 hour of a dose, contact your healthcare provider for instructions.,Report any vision changes, such as blurred vision or difficulty focusing, immediately.,Avoid alcohol and limit caffeine intake as they may increase gastrointestinal side effects.,Use effective contraception during treatment if you are of childbearing potential.,Do not take antacids or kaolin within 4 hours of this medication.,Seek medical attention if you experience signs of allergic reaction: rash, hives, swelling, or difficulty breathing.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about FANSIDAR vs ARALEN HYDROCHLORIDE, answered by our medical review team.
FANSIDAR is a Antimalarial that works by Fansidar combines sulfadoxine, a sulfonamide dihydrofolate reductase inhibitor, and pyrimethamine, a dihydrofolate reductase inhibitor, synergistically inhibiting folate synthesis in Plasmodium species, leading to nucleic acid synthesis inhibition and parasite death.. ARALEN HYDROCHLORIDE is a Antimalarial that works by Chloroquine, a 4-aminoquinoline, accumulates in acidic organelles such as lysosomes and food vacuoles of malaria parasites, raising p H and inhibiting hemozoin polymerization, which leads to toxic heme accumulation and parasite death. It also has anti-inflammatory and immunomodulatory effects by inhibiting TLR signaling and cytokine production.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between FANSIDAR and ARALEN HYDROCHLORIDE depend on the specific clinical indication. These are both Antimalarial agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of FANSIDAR is: For acute uncomplicated malaria: 3 tablets (25 mg pyrimethamine + 500 mg sulfadoxine per tablet) orally as a single dose on Day 0 and Day 1 (total 6 tablets); alternatively, 3 tablets as a single dose. For severe malaria: 3 tablets orally as a single dose, repeated at weekly intervals if necessary.. The standard adult dose of ARALEN HYDROCHLORIDE is: Chloroquine phosphate 500 mg (300 mg base) orally once weekly for prophylaxis; 600 mg base (1 g phosphate) orally initially, followed by 300 mg base (500 mg phosphate) at 6, 24, and 48 hours for treatment of malaria.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between FANSIDAR and ARALEN HYDROCHLORIDE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. FANSIDAR is classified as Category C. Pregnancy Category C. First trimester: Contraindicated due to sulfadoxine-pyrimethamine's antifolate activity, associated with neural tube defects and major congenital malformation. ARALEN HYDROCHLORIDE is classified as Category C. Chloroquine hydrochloride crosses the placenta. First trimester: associated with increased risk of spontaneous abortion and congenital abnormalities (cochleovestibular and ocular) . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.