Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
HALOTHANE vs ARALEN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Halothane is a volatile halogenated hydrocarbon anesthetic that acts as a positive allosteric modulator of GABA-A receptors and glycine receptors, and inhibits NMDA and nicotinic acetylcholine receptors, leading to neuronal hyperpolarization and general anesthesia.
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.
Induction and maintenance of general anesthesia,Sedation in intensive care (off-label),Status asthmaticus (off-label, due to bronchodilation)
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)
Induction: 0.5-3% in oxygen or oxygen-nitrous oxide mixture, titrated to effect; Maintenance: 0.5-2% in oxygen or oxygen-nitrous oxide mixture.
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.
Terminal elimination half-life approximately 5-10 hours post-anesthesia, with a slower terminal phase (up to 3 days) due to redistribution from fat stores. Clinically, washout is rapid initially but prolonged exposure in obese patients may lead to detectable levels for days.
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.
Halothane is metabolized in the liver primarily by cytochrome P450 2E1 (CYP2E1) to trifluoroacetic acid and bromide ion; reductive metabolism also produces chloride ions and free radicals.
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.
Primarily eliminated via pulmonary excretion (60-80% unchanged); approximately 20% metabolized in liver via CYP2E1, with metabolites excreted renally (trifluoroacetic acid, chloride, bromide). Only about 0.5% excreted unchanged in urine. Fecal excretion negligible.
Primarily renal (approximately 70% as unchanged drug); minor biliary/fecal (about 10-20%).
Approximately 20-30% bound to plasma proteins, primarily albumin and lipoproteins.
Approximately 50-60% bound; primarily to albumin and alpha-1-acid glycoprotein.
Volume of distribution at steady state (Vdss) approximately 2-5 L/kg; large Vd indicates extensive tissue distribution, especially to adipose tissue, brain, and muscle.
Very large, 100-200 L/kg; extensive tissue distribution (liver, spleen, kidney, lungs, melanin-containing tissues).
100% bioavailable via inhalation (only route of administration). Oral bioavailability not applicable.
Oral: 80-90%.
No specific dose adjustment required for renal impairment; use with caution due to potential nephrotoxicity from fluoride ions.
For malaria prophylaxis: No adjustment necessary. For treatment: If Cr Cl < 10 m L/min, reduce dose by 50%.
Child-Pugh Class A: no adjustment; Child-Pugh Class B and C: avoid use; contraindicated in patients with hepatic impairment or history of halothane-induced hepatotoxicity.
No formal guidelines; use caution in severe hepatic impairment due to potential accumulation. Consider dose reduction in Child-Pugh class C.
Induction: 0.5-2% in oxygen or oxygen-nitrous oxide mixture, gradually increased; Maintenance: 0.3-1.5% as needed. Use lowest effective dose.
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.
Reduce dose by 25-50% due to increased sensitivity and reduced clearance; monitor hemodynamics closely.
No specific adjustments; consider age-related renal impairment and potential increased risk of QT prolongation. Monitor for cardiac effects.
Halothane can cause hepatic necrosis, which may be fatal. Fatalities have occurred in patients with previous halothane exposure. Avoid repeat exposure within 3-6 months.
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.
Hepatotoxicity (halothane hepatitis), malignant hyperthermia, cardiac arrhythmias (sensitizes myocardium to catecholamines), respiratory depression, hypotension, increased intracranial pressure.
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).
Hypersensitivity to halothane, known or suspected susceptibility to malignant hyperthermia, history of unexplained jaundice or fever after halothane, hepatic dysfunction following previous halothane exposure, pregnancy (relative, especially first trimester).
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).
No specific food interactions. However, fasting is required before anesthesia to reduce aspiration risk. Alcohol should be avoided for at least 24 hours post-anesthesia due to additive CNS depression.
Avoid grapefruit juice as it may increase chloroquine levels. No other significant food interactions.
Halothane is classified as FDA Pregnancy Category C. Animal studies have shown teratogenic effects, but adequate human studies are lacking. First trimester exposure is associated with a potential increased risk of congenital malformations based on limited epidemiological data. Second and third trimester use may cause fetal depression and uterine atony; prolonged exposure can lead to neonatal respiratory depression. Avoid use during pregnancy unless clearly needed.
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.
Halothane is excreted into breast milk in small amounts. The milk-to-plasma (M/P) ratio is approximately 0.4. Due to low oral bioavailability, risks to the nursing infant are minimal. However, caution is advised as effects on the infant have not been fully studied. Consider pumping and discarding milk for 24-48 hours after anesthesia to minimize exposure.
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.
No specific dose adjustment is recommended, but pregnancy alters pharmacokinetics: increased volume of distribution and decreased protein binding may require higher initial doses to achieve desired anesthetic depth. However, due to increased sensitivity to myocardial depression and uterine relaxation, use the minimum effective dose. Reduce concentration as needed to maintain uterine perfusion and avoid fetal hypoxia.
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.
Halothane is a volatile halogenated hydrocarbon anesthetic. It sensitizes the myocardium to catecholamines, increasing risk of arrhythmias; avoid epinephrine use. Associated with halothane hepatitis (immune-mediated hepatotoxicity), especially with multiple exposures. Malignant hyperthermia trigger; have dantrolene ready. Use with caution in patients with increased intracranial pressure as it can elevate ICP. Use with low fresh gas flows to minimize pollution and cost.
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.
This medication will make you unconscious for surgery. You will not feel pain or remember the procedure.,You must fast before anesthesia; do not eat or drink for at least 6-8 hours before surgery.,Tell your anesthesiologist about any liver problems or previous reactions to anesthesia.,Notify your doctor if you have a personal or family history of malignant hyperthermia.,Avoid alcohol for at least 24 hours after anesthesia.,Do not drive or operate machinery for 24 hours after receiving halothane.
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.
"Efonidipine, a dihydropyridine calcium channel blocker, inhibits L-type and T-type calcium channels, leading to vasodilation and reduced myocardial contractility. Halothane, a volatile inhalational anesthetic, depresses myocardial function and sensitizes the myocardium to catecholamines, increasing the risk of arrhythmias. Concurrent use can result in additive negative inotropic effects and profound hypotension, potentially leading to cardiovascular collapse."
"Halothane, a volatile anesthetic, can inhibit the cytochrome P450 enzyme CYP2B6, which is primarily responsible for the metabolism of bupropion, an antidepressant and smoking cessation aid. This inhibition leads to decreased clearance of bupropion, resulting in elevated plasma concentrations that increase the risk of dose-dependent adverse effects such as seizures, anxiety, and insomnia. Clinically, patients may exhibit heightened neuropsychiatric toxicity and reduced seizure threshold, particularly during and after halothane anesthesia."
"Halothane, a volatile halogenated anesthetic, inhibits cytochrome P450 (CYP) isoenzymes, particularly CYP2C19, which is crucial for the hepatic bioactivation of clopidogrel to its active metabolite. Concomitant administration can lead to reduced plasma concentrations of the active thiol metabolite of clopidogrel, diminishing its antiplatelet effect and increasing the risk of thrombotic events such as stent thrombosis or myocardial infarction in patients with coronary artery disease. This interaction is especially significant in patients undergoing surgery where halothane is used for anesthesia while clopidogrel is indicated for recent acute coronary syndrome or percutaneous coronary intervention."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about HALOTHANE vs ARALEN, answered by our medical review team.
HALOTHANE is a General Anesthetic that works by Halothane is a volatile halogenated hydrocarbon anesthetic that acts as a positive allosteric modulator of GABA-A receptors and glycine receptors, and inhibits NMDA and nicotinic acetylcholine receptors, leading to neuronal hyperpolarization and general anesthesia.. 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.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between HALOTHANE and ARALEN 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 HALOTHANE is: Induction: 0.5-3% in oxygen or oxygen-nitrous oxide mixture, titrated to effect; Maintenance: 0.5-2% in oxygen or oxygen-nitrous oxide mixture.. 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.. 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 HALOTHANE and ARALEN 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. HALOTHANE is classified as Category C. Halothane is classified as FDA Pregnancy Category C. Animal studies have shown teratogenic effects, but adequate human studies are lacking. First trimester exposure is associated w. 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. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.