Quinethazone and Lisinopril: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Quinethazone
No brand names on recordLisinopril
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.
Quinethazone is a water pill (diuretic) that lowers your blood pressure partly by helping your body get rid of extra salt and fluid. Lisinopril is a blood pressure medicine too, but it works a different way by relaxing your blood vessels. When you take both, especially when lisinopril is first started, your blood pressure can drop more than expected.
You might feel dizzy or lightheaded, particularly when you stand up quickly. The good news is this usually settles down after the first dose or two. Your care team can manage this easily by adjusting your dose, checking your blood pressure, and guiding you on how to start. Let them know if you feel faint.
Effect: Additive/excessive blood pressure reduction, most notably first-dose hypotension, when the ACE inhibitor lisinopril is initiated in a patient already on the thiazide-type diuretic quinethazone.
Mechanism: Pharmacodynamic. Diuretic-induced volume/sodium depletion plus ACE-inhibitor vasodilation and RAAS suppression can produce severe postural hypotension.
- Direction: Enhanced hypotensive/PD effect (not a CYP interaction; neither is a prodrug relevant here).
- Onset: Rapid (often first dose).
- Evidence: Theoretical/expected class effect; usually transient.
- Management: Consider reducing or holding the diuretic or liberalizing sodium before starting; otherwise use a low lisinopril starting dose. Monitor supine/standing BP.
What happens
Reduction of blood pressure
Interaction Deep Dive
When an ACE inhibitor is started in patients already receiving diuretics, blood pressure may fall to an excessive degree3. The addition of ACE inhibitors to diuretic regimens has been associated with reports of severe postural hypotension. This effect is seen more frequently with loop diuretics, and first dose hypotension often occurs in individuals whose sodium levels or volume status are depleted as a result of diuretic use or dietary sodium restriction. Typically, this drop in blood pressure is transient6271. To lessen the chance of hypotensive effects, the diuretic can be reduced or stopped, or salt intake can be raised, prior to beginning ACE inhibitor treatment. When such steps cannot be taken, the initial ACE inhibitor dose should be lowered3.
Why it happens (mechanism)
Vasodilation and relative intravascular volume depletion
How to manage this interaction
Keep taking both medications exactly as prescribed unless your prescriber tells you otherwise. This interaction is most likely right around the time lisinopril is first started or its dose is raised.
- Your care team may lower or briefly pause the diuretic, or start lisinopril at a lower dose, to soften the initial blood pressure drop.
- They may monitor your blood pressure more closely at first, including checking it sitting and standing.
- Stand up slowly to avoid dizziness.
- Tell your pharmacist or prescriber if you feel faint, very dizzy, or lightheaded. The effect is usually short-lived and manageable.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) In a randomized crossover trial (N=19) evaluating the simultaneous use of hydrochlorothiazide and enalapril in elderly patients (62 to 84 years), the pharmacokinetics of enalapril remained relatively unchanged by hydrochlorothiazide; however, there was a significant rise in AUC (0 to 24 hours) along with a significant decrease in the renal clearance of enalaprilat 4.
b) A slight decline in peak serum concentrations of perindoprilat, together with a reduction in the proportion of the perindopril dose eliminated as perindoprilat in the urine, has been documented when perindopril and hydrochlorothiazide are given together 5.
Common questions
Can I take Quinethazone and Lisinopril together?
Starting lisinopril while already on the diuretic quinethazone can cause a bigger-than-expected drop in blood pressure at first, so watch for dizziness and let your care team adjust the dose and monitor you. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Quinethazone and Lisinopril interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How is the Quinethazone and Lisinopril interaction managed?
Keep taking both medications exactly as prescribed unless your prescriber tells you otherwise. This interaction is most likely right around the time lisinopril is first started or its dose is raised. Your care team may lower or briefly pause the diuretic, or start lisinopril at a lower dose, to soften the initial blood pressure drop. They may monitor your blood pressure more closely at first, incl… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Quinethazone or Lisinopril 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 anything you'd monitor while I'm on both?
References (7)
- Vlasses PH, Ferguson RK, & Chatterjee K: Captopril: clinical pharmacology and benefit-to-risk ratio in hypertension and congestive heart failure. Pharmacotherapy 1982; 2:1-17. PubMed
- Gluck Z, Beretta-Piccoli C, & Reubi FC: Long-term effects of captopril on renal function in hypertensive patients. Eur J Clin Pharmacol 1984; 26:315-323. PubMed
- Product Information: QBRELIS(TM) oral solution, lisinopril oral solution. Silvergate Pharmaceuticals (per manufacturer), Greenwood Village, CO, 2016. DailyMed
- Weisser K, Schloos J, Jakob S, et al: The influence of hydrochlorothiazide on the pharmacokinetics of enalapril in elderly patients. Eur J Clin Pharmacol 1992; 43:173-177. PubMed
- Todd PA & Fitton A: Perindopril: a review of its pharmacological properties and therapeutic use in cardiovascular disorders. Drugs 1991; 42:90-114.
- Atkinson AB, Brown JJ, Morton JJ, et al: Captopril in a hyponatremic hypertensive; need for caution initiating therapy (letter). Lancet 1979; 1:557-558.
- Pandhi P, Mondal S, Sharma BK, et al: Low dose captopril alone and in combination with hydrochlorothiazide in treatment of mild to moderate essential hypertension. Int J Clin Pharmacol Ther Toxicol 1986; 24:294-297.
Keep reading about Quinethazone
Keep reading about Lisinopril
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