Ketanserin and Furosemide Injection: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Furosemide Injection
Ketanserin
No brand names on record
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.
What happens
Ventricular arrhythmias
Interaction Deep Dive
Concurrent administration of ketanserin and potassium-wasting diuretics may result in ventricular arrhythmias21. In one large randomized, placebo-controlled, double-blind study, ketanserin and potassium-wasting diuretics produced additive QT interval prolongation. Diuretic-induced hypokalemia and high doses of ketanserin may have exacerbated the arrhythmias in the affected patients 1. One study of the effects of hydrochlorothiazide on ketanserin pharmacokinetics found no significant difference in the kinetics of ketanserin alone compared with ketanserin plus hydrochlorothiazide, and failed to show any significant effect on the QT interval. However, this study utilized single doses of ketanserin and hydrochlorothiazide only 3.
Why it happens (mechanism)
Diuretic-induced hypokalemia; theoretical additive QT prolongation
Literature reports
3 reports — tap to read
a) In a large, double-blind trial involving 3899 patients in 14 countries, concurrent administration of ketanserin with potassium-losing diuretics was associated with a significant increase in the number of deaths from cardiovascular causes in patients with claudication 1. Ketanserin produced QT prolongation in this study (mean of 18 ms), as did potassium-losing diuretics, and their combination produced a significantly longer prolongation of the QT interval (mean 30 ms) than ketanserin alone. When comparing the number of sudden deaths in the patients taking potassium-losing diuretics, 16 patients receiving ketanserin died, versus only 5 patients on placebo. In the group receiving potassium-sparing diuretics, three patients in both the ketanserin and the placebo group experienced sudden death, and in the group receiving no diuretics, 17 patients on ketanserin and 15 patients on placebo had sudden death. Ketanserin was administered at a relatively high dose (40 mg orally three times daily) in this study. These combined effects on the QT interval, in addition to the reduction in potassium concentrations induced by the diuretics, may have precipitated or worsened ventricular arrhythmias in the affected patients.
b) In one study involving 221 patients, the QT prolongation induced by ketanserin did not appear to be associated with an increased risk of ventricular arrhythmias. Subjects were given ketanserin 20 mg twice daily for one week followed by ketanserin 40 mg twice daily for three weeks or placebo. The QTc interval was prolonged with ketanserin (mean 400 ms to 418 ms) but not with placebo. In the ketanserin group, 30% of patients had a QTc prolongation greater than 30 ms. However, malignant forms of ventricular arrhythmias are possible in particular patients with other contributing factors to their development, including the use of potassium-wasting diuretics 2.
c) A randomized, double-blind, cross-over, placebo-controlled study found no significant differences in maximum concentration, time to peak, or area under the concentration-time curve (AUC) in patients receiving a single 20 mg dose of ketanserin compared with those coadministered a single 20 mg dose of ketanserin plus a 25 mg hydrochlorothiazide dose. Twenty-two males with essential hypertension participated in the study. Neither ketanserin alone nor the combination significantly affected QTc interval, heart rate, or serum concentrations of sodium, potassium, magnesium, calcium, or chloride 3.
Common questions
Can I take Ketanserin and Furosemide Injection together?
Ventricular arrhythmias Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ketanserin and Furosemide Injection interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
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 Ketanserin or Furosemide Injection 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 (3)
- Anon: Prevention of atherosclerotic complications: controlled trial of ketanserin. Prevention of Atherosclerotic Complications with Ketanserin Trial Group. Br Med J 1989; 298:424-430. DOI
- Zehender M, Meinertz T, Hohnloser S, et al: Incidence and clinical relevance of QT prolongation caused by the new selective serotonin antagonist ketanserin. Am J Cardiol 1989; 63:826-832. PubMed
- Botha JH, McFadyen, Leary WP, et al: No effect of single-dose hydrochlorothiazide on the pharmacokinetics of single-dose ketanserin. Curr Ther Res 1991; 49:225-230.
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