Diltiazem with Quinidine Interaction Details

Brand Names Associated with Diltiazem

Brand Names Associated with Quinidine

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Nov 13, 2023

Interaction Effect

Quinidine toxicity (ventricular arrhythmias, hypotension, exacerbation of heart failure)

Interaction Summary

In a controlled study of 12 healthy male volunteers, pretreatment with diltiazem resulted in increased quinidine area under the concentration-time curve (AUC), increased quinidine half-life, decreased quinidine clearance, increased QTc and PR intervals, and decreased heart rate and diastolic pressure. Conversely,  observed no alteration of the kinetics of either drug during coadministration . More studies with these two agents are needed to confirm the extent of this interaction.

Severity

Moderate

Onset

Rapid

Evidence

Theoretical

How To Manage Interaction

Monitor patients closely for symptoms of quinidine toxicity, including laboratory confirmation of alterations in serum quinidine levels. Dose adjustments may be required.

Mechanism Of Interaction

Inhibition of quinidine metabolism

Literature Reports

A) In a controlled study of 12 healthy male volunteers, the pharmacokinetic and pharmacodynamic interactions between diltiazem and quinidine were assessed. Subjects received single oral doses of quinidine 200 mg or diltiazem 60 mg, alone and on a background of the other drug, in a crossover study. Background treatment was quinidine 100 mg twice daily or diltiazem 90 mg sustained-release twice a daily for two days before the study day. Blood samples were taken throughout the study and analyzed for serum concentrations of diltiazem and quinidine. Pretreatment with diltiazem increased the area under the concentration-time curve (AUC) for quinidine by 51%. Average elimination half-life of quinidine was increased 36% and the oral clearance of quinidine was decreased by 33%. Pharmacodynamic measurements revealed that pretreatment with diltiazem increased QTc and PR intervals and decreased heart rate and systolic blood pressure. Pretreatment with quinidine did not significantly affect the disposition of diltiazem . Conversely, concomitant administration of diltiazem and quinidine in healthy volunteers resulted in no alteration of the kinetics of either drug .

Diltiazem Overview

• Diltiazem is used to treat high blood pressure and to control angina (chest pain). Diltiazem is in a class of medications called calcium-channel blockers. It works by relaxing the blood vessels so the heart does not have to pump as hard. It also increases the supply of blood and oxygen to the heart.

• High blood pressure is a common condition, and when not treated it can cause damage to the brain, heart, blood vessels, kidneys, and other parts of the body. Damage to these organs may cause heart disease, a heart attack, heart failure, stroke, kidney failure, loss of vision, and other problems. In addition to taking medication, making lifestyle changes will also help to control your blood pressure. These changes include eating a diet that is low in fat and salt, maintaining a healthy weight, exercising at least 30 minutes most days, not smoking, and using alcohol in moderation.

Quinidine Overview

• Quinidine is used to treat certain types of irregular heartbeats. Quinidine is in a class of medications called antiarrhythmic medications. It works by making your heart more resistant to abnormal activity.

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.

Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.

Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.

Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

Where Does Our Information Come From?

Information for our drug interactions is compiled from several drug compendia, including:

• Gold Standard Drug Database
• Micromedex
• Lexicomp
• DrugBank

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.