Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ARALEN vs ALDORIL 25
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Chloroquine, a 4-aminoquinoline, accumulates in acidic organelles such as food vacuoles of malaria parasites, inhibiting heme polymerase and preventing the conversion of toxic heme to hemozoin. It also interferes with DNA synthesis and repair by intercalating into DNA. Additionally, it has immunomodulatory effects via inhibition of Toll-like receptors and cytokine production.
Combination of methyldopa, a centrally acting alpha-2 adrenergic agonist that reduces sympathetic outflow, and hydrochlorothiazide, a thiazide diuretic that inhibits sodium reabsorption in the distal convoluted tubule, reducing plasma volume.
Treatment of uncomplicated malaria caused by susceptible strains of Plasmodium vivax, P. malariae, P. ovale, and P. falciparum,Prophylaxis of malaria in areas with chloroquine-sensitive P. falciparum,Treatment of extraintestinal amebiasis (as amebicide) and giardiasis (off-label),Disease-modifying antirheumatic drug (DMARD) for rheumatoid arthritis and lupus erythematosus (off-label)
Hypertension
Adults: 500 mg (300 mg base) orally once weekly on the same day each week for prophylaxis of malaria; 1 g (600 mg base) orally initially, followed by 500 mg (300 mg base) at 6, 24, and 48 hours for treatment of acute malaria.
Oral: 1 tablet (hydrochlorothiazide 25 mg/methyldopa 250 mg) twice daily; increase as needed to max 2 tablets twice daily.
Terminal elimination half-life ranges from 30 to 60 days (mean ~45 days) due to extensive tissue binding; clinical context: prolonged half-life allows weekly dosing for malaria prophylaxis.
7-16 hours (terminal). In renal impairment, half-life may exceed 24 hours, requiring dose adjustment.
Chloroquine is extensively metabolized in the liver via cytochrome P450 enzymes, primarily CYP2C8 and CYP3A4, to active metabolites such as desethylchloroquine. It has a long elimination half-life of approximately 1-2 months.
Methyldopa is metabolized primarily via hepatic conjugation and renal excretion; hydrochlorothiazide is not significantly metabolized and is excreted unchanged in urine.
Primarily renal (approximately 70% as unchanged drug); minor biliary/fecal (about 10-20%).
Renal: ~85% unchanged. Biliary/fecal: ~15% as metabolites.
Approximately 50-60% bound; primarily to albumin and alpha-1-acid glycoprotein.
Methyldopa: less than 10% bound to plasma proteins. Hydrochlorothiazide: ~70% bound to plasma proteins (primarily albumin).
Very large, 100-200 L/kg; extensive tissue distribution (liver, spleen, kidney, lungs, melanin-containing tissues).
Methyldopa: 0.3-0.6 L/kg (distributes widely, including CNS). Hydrochlorothiazide: 0.8-1.5 L/kg (distributes into extracellular fluid).
Oral: 80-90%.
Methyldopa: oral bioavailability ~25% (first-pass metabolism). Hydrochlorothiazide: oral bioavailability ~60-80%.
For malaria prophylaxis: No adjustment necessary. For treatment: If Cr Cl < 10 m L/min, reduce dose by 50%.
GFR 30-50 m L/min: use with caution, reduce dose. GFR <30 m L/min: not recommended.
No formal guidelines; use caution in severe hepatic impairment due to potential accumulation. Consider dose reduction in Child-Pugh class C.
Child-Pugh A: no adjustment; Child-Pugh B or C: contraindicated due to methyldopa hepatotoxicity risk.
Prophylaxis: 5 mg/kg base (8.3 mg/kg salt) orally once weekly, max 300 mg base. Treatment: 10 mg/kg base (16.7 mg/kg salt) orally initially, followed by 5 mg/kg base at 6, 24, and 48 hours, max 600 mg base on day 1.
Not established; avoid use in children.
No specific adjustments; consider age-related renal impairment and potential increased risk of QT prolongation. Monitor for cardiac effects.
Start at lowest dose (1 tablet daily); monitor for orthostatic hypotension, sedation, and electrolyte imbalance.
Retinopathy: Irreversible retinal damage including retinopathy and visual disturbances; risk increases with cumulative dose and duration of use; contraindicated in patients with pre-existing retinopathy; baseline and periodic ophthalmologic exams required.
None
Retinopathy risk with prolonged use; cardiac effects including conduction disorders (e.g., QT prolongation) and cardiomyopathy; exacerbation of psoriasis and porphyria; neuropsychiatric effects (e.g., psychosis, seizures); hematologic toxicity (eg, agranulocytosis, aplastic anemia); hypoglycemia; myopathy; ototoxicity. Use with caution in hepatic or renal impairment, G6PD deficiency, and pregnancy (benefit vs risk).
May cause sedation, depression, positive direct Coombs test, hemolytic anemia, hepatotoxicity, fluid/electrolyte imbalance, and sensitivity reactions; monitor liver function, CBC, and electrolytes.
Hypersensitivity to chloroquine or 4-aminoquinolines; pre-existing retinopathy of any etiology; concurrent use with other agents causing retinal toxicity (e.g., hydroxychloroquine, tamoxifen); porphyria; psoriasis (relative, may exacerbate); neuromyopathy (relative); severe hepatic or renal impairment (relative).
Hypersensitivity to methyldopa, hydrochlorothiazide, or sulfonamides; active hepatic disease; anuria; history of methyldopa-induced liver disorders.
Avoid grapefruit juice as it may increase chloroquine levels. No other significant food interactions.
Avoid high-sodium foods to optimize antihypertensive effect. Limit alcohol intake. Do not consume large amounts of potassium-rich foods (e.g., bananas, oranges, spinach) unless advised by a healthcare provider, as hydrochlorothiazide can alter potassium levels.
Pregnancy category C. First trimester: No conclusive evidence of major malformations in human studies, but animal studies show embryotoxicity and fetotoxicity. Second and third trimesters: Risk of sensorineural hearing loss, vestibular damage, and retinal toxicity in the fetus if used for prolonged periods or at high doses; accumulation in fetal ocular tissues reported.
First trimester: Limited human data, but animal studies show no teratogenicity at therapeutic doses. Second and third trimesters: Associated with fetal hypotension, oligohydramnios, and renal dysfunction due to methyldopa component. Hydrochlorothiazide may cause fetal electrolyte imbalances.
Excreted in breast milk in small amounts (M/P ratio approximately 0.44). American Academy of Pediatrics considers compatible with breastfeeding, but caution is advised in infants with glucose-6-phosphate dehydrogenase deficiency or hemolytic disease. Monitor infant for rash, retinal changes, and hemolysis.
Methyldopa is excreted in breast milk with M/P ratio of approximately 0.2-0.5; hydrochlorothiazide M/P ratio ~0.5-0.6. Considered compatible with breastfeeding by AAP, but monitor infant for hypotension and electrolyte disturbances.
No specific dose adjustment recommended for pregnancy; pharmacokinetic changes (increased volume of distribution, decreased plasma concentrations) may require therapeutic drug monitoring, but empirical dose adjustments are not established. Use lowest effective dose and shortest duration.
No standard dose adjustment required, but increased plasma volume in pregnancy may necessitate higher doses of methyldopa. Monitor clinical response and adjust accordingly.
Chloroquine (Aralen) can cause retinal toxicity; cumulative dose should not exceed 200g. Use with caution in G6PD deficiency. Can prolong QTc interval; avoid with other QTc-prolonging drugs.
ALDORIL 25 is a fixed-dose combination of methyldopa (250 mg) and hydrochlorothiazide (25 mg). Monitor for hypotension, especially during initial therapy or with volume depletion. Methyldopa may cause a positive direct Coombs test and hemolytic anemia; discontinue if anemia develops. Hydrochlorothiazide can cause electrolyte imbalances, hyperglycemia, and hyperuricemia. Avoid use in patients with pheochromocytoma or active liver disease.
Take with food to reduce gastrointestinal upset.,Do not exceed prescribed dose; overdose can be fatal.,Report any vision changes immediately; regular eye exams are required.,Avoid alcohol as it may increase risk of liver toxicity.,Inform your doctor if you have a history of heart rhythm problems.
Take this medication exactly as prescribed, usually once or twice daily.,Rise slowly from sitting or lying to prevent dizziness from low blood pressure.,Avoid alcohol, which can increase dizziness and drowsiness.,Report any signs of infection, unusual tiredness, or yellowing of skin/eyes.,Use sun protection as hydrochlorothiazide may increase sun sensitivity.,Do not use potassium supplements or salt substitutes without consulting your doctor.
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 ARALEN vs ALDORIL 25, answered by our medical review team.
ARALEN is a Antimalarial that works by Chloroquine, a 4-aminoquinoline, accumulates in acidic organelles such as food vacuoles of malaria parasites, inhibiting heme polymerase and preventing the conversion of toxic heme to hemozoin. It also interferes with DNA synthesis and repair by intercalating into DNA. Additionally, it has immunomodulatory effects via inhibition of Toll-like receptors and cytokine production.. ALDORIL 25 is a Antihypertensive Combination that works by Combination of methyldopa, a centrally acting alpha-2 adrenergic agonist that reduces sympathetic outflow, and hydrochlorothiazide, a thiazide diuretic that inhibits sodium reabsorption in the distal convoluted tubule, reducing plasma volume.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ARALEN and ALDORIL 25 depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ARALEN is: Adults: 500 mg (300 mg base) orally once weekly on the same day each week for prophylaxis of malaria; 1 g (600 mg base) orally initially, followed by 500 mg (300 mg base) at 6, 24, and 48 hours for treatment of acute malaria.. The standard adult dose of ALDORIL 25 is: Oral: 1 tablet (hydrochlorothiazide 25 mg/methyldopa 250 mg) twice daily; increase as needed to max 2 tablets twice daily.. 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 ARALEN and ALDORIL 25 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. ARALEN is classified as Category C. Pregnancy category C. First trimester: No conclusive evidence of major malformations in human studies, but animal studies show embryotoxicity and fetotoxicity. Second and third tri. ALDORIL 25 is classified as Category C. First trimester: Limited human data, but animal studies show no teratogenicity at therapeutic doses. Second and third trimesters: Associated with fetal hypotension, oligohydramnios. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.