Drug Interaction Report

Chloroquine and Astemizole: Interaction Details

A pharmacist-reviewed analysis of the Chloroquine and Astemizole interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Chloroquine

Aralen®
+

Astemizole

No brand names on record
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
How we grade severity & evidence

Severity levels

  • Contraindicated: These should generally not be used together.
  • Major: Potentially serious — often needs a change or close monitoring.
  • Moderate: Can be significant — usually manageable with monitoring.
  • Minor: Usually limited clinical impact.

Evidence grades

  • Established: Well documented — supported by controlled studies or strong clinical data.
  • Probable: Good supporting evidence, though not definitively proven.
  • Suspected: Some evidence suggests this interaction, but it is not well established.
  • Possible: Limited or conflicting evidence; the interaction may occur.
  • Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 332 documented Chloroquine interactions, 294 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
theoretical
Severity
Major

What happens

An increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest)

Interaction Deep Dive

Astemizole has been shown to prolong the QTc interval at the recommended therapeutic dose6. Even though no formal drug interaction studies have been done, the coadministration of astemizole and other drugs known to prolong the QTc interval, including chloroquine, is not recommended 7.

Why it happens (mechanism)

Additive effects on QT prolongation

Literature reports

1 report — tap to read

a) EKG changes such as T-wave inversion, T-wave flattening, and QT interval prolongation, can occur following therapeutic doses of chloroquine 34. In 18 of 53 patients receiving oral chloroquine 250 mg twice to three times daily, EKG abnormalities occurred after 10 to 21 days. Cessation of the drug normalized or improved the EKG pattern. Widening of the QRS interval in association with S-T segment depression and QT prolongation have been observed following acute overdoses 512.

Common questions

Can I take Chloroquine and Astemizole together?

An increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest) Always confirm with your pharmacist or prescriber before making any change.

How serious is the Chloroquine and Astemizole interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

Questions for your pharmacist

  • Does my dose of Chloroquine or Astemizole need adjusting while I take them together?
  • What symptoms should prompt me to call you or my prescriber right away?
  • Does the timing of my doses matter for this combination?
  • Is there a safer alternative to one of these medications for me?

References (7)

  1. Michael TAD & Aiwazzadeh S: The effects of acute chloroquine poisoning with special reference to the heart. Am Heart J 1970; 79:831. PubMed
  2. Sanghir LM & Mathur BB: Electrocardiogram after chloroquine and emetine. Circulation 1965; 32:281. PubMed
  3. Product Information: Aralen(R), chloroquine. Sanofi Pharmaceuticals, New York, NY, 2001. DailyMed
  4. Powell SH: The cardiotoxicity of systemic amebicides. A comparative electrocardiographic study. Am J Trop Med 1967; 16:447. PubMed
  5. Belghiti J, Belghiti D, Amedome A, et al: Chloroquine intoxication with cardiac disturbances: effect of isoprenaline (letter). Nouv Presse Med 1975; 4:971.
  6. Product Information: Hismanal(R), astemizole. Janssen Pharmaceutica, Inc. Titusville, NJ, 1996.
  7. Product Information: Aralen(R), chloroquine. Sanofi Pharmaceuticals, New York, NY, 2001. DailyMed
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Chloroquine

Keep reading about Chloroquine

All Chloroquine interactions (332) Chloroquine drug information
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Astemizole

Keep reading about Astemizole

All Astemizole interactions (63)
Also serious with: Ketoconazole Topical Oxaliplatin Injection Glasdegib Dasatinib
Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Chloroquine + Activated Charcoal Hibiscus Sabdariffa Biofeedback Coffee Charcoal Dendrobium European Mandrake Fever Bark Ginkgo + 21 more
Astemizole + Activated Charcoal American Hellebore Arsenic Cesium Ephedra Grapefruit Sida Cordifolia Bitter Orange + 22 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.