Diltiazem with Efavirenz Interaction Details

Brand Names Associated with Diltiazem

Brand Names Associated with Efavirenz

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

Interaction Effect

Decreased exposures and plasma concentrations of diltiazem and its metabolites

Interaction Summary

Coadministration of efavirenz (a CYP3A4 inducer) and diltiazem (a CYP3A4 substrate) resulted in significantly decreased concentrations of diltiazem and its principal metabolites, desacetyl diltiazem and N-monodesmethyl diltiazem. Therefore, use caution when these 2 drugs are coadministered and adjust diltiazem doses based on clinical response. Because diltiazem only slightly increased plasma concentrations of efavirenz, dose adjustment of efavirenz is not necessary when these two drugs are coadministered.

Severity

Moderate

Onset

Unspecified

Evidence

Established

How To Manage Interaction

The concomitant use of diltiazem and efavirenz resulted in significantly reduced exposures and plasma concentrations of diltiazem and its two principal metabolites. Therefore, use caution if diltiazem and efavirenz are coadministered. Although no dose adjustment is necessary for efavirenz, diltiazem doses may need to be adjusted based on clinical response.

Mechanism Of Interaction

Induction of CYP3A4-mediated diltiazem metabolism by efavirenz

Literature Reports

A) In pharmacokinetic studies, efavirenz significantly decreased exposures and plasma concentrations of diltiazem and its 2 principle metabolites, desacetyl diltiazem and N-monodesmethyl diltiazem. In 13 subjects, coadministration of oral efavirenz 600 mg daily for 14 days and diltiazem 240 mg daily for 21 days resulted in mean decreases in plasma Cmax, AUC, and Cmin of diltiazem by 60% (90% confidence interval (CI), 50% to 68%), 69% (90% CI, 55% to 79%), and 63% (90% CI, 44% to 75%), respectively. Additionally, the Cmax, AUC, and Cmin of the diltiazem's metabolites, desacetyl diltiazem and N-monodesmethyl diltiazem, were also decreased on average by 64% (90% CI, 57% to 69%), 75% (90% CI, 59% to 84%), and 62% (90% CI, 44% to 75%), respectively, for desacetyl diltiazem, and by 28% (90% CI, 7% to 44%), 37% (90% CI, 17% to 52%), and 37% (90% CI, 17% to 52%), respectively, for N-monodesmethyl diltiazem. Efavirenz pharmacokinetics were not significantly altered when studied in 12 subjects who received diltiazem 240 mg daily for 14 days with efavirenz 600 mg daily for 28 days. The mean Cmax, AUC, and Cmin of efavirenz increased by 16% (90% CI, 6% to 26%), 11% (90% CI, 5% to 18%), and 13% (90% CI, 1% to 26%), respectively .

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.

Efavirenz Overview

• Efavirenz is used along with other medications to treat human immunodeficiency virus (HIV) infection. Efavirenz is in a class of medications called non-nucleoside reverse transcriptase inhibitors (NNRTIs). It works by decreasing the amount of HIV in the blood. Although efavirenz does not cure HIV, it may decrease your chance of developing acquired immunodeficiency syndrome (AIDS) and HIV-related illnesses such as serious infections or cancer. Taking these medications along with practicing safer sex and making other life-style changes may decrease the risk of transmitting (spreading) the HIV virus to other people.

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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.