Losartan with Rifampin Interaction Details

Brand Names Associated with Losartan

Brand Names Associated with Rifampin

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Nov 05, 2023

Interaction Effect

Reduced losartan efficacy

Interaction Summary

Losartan is an angiotensin II subtype 1 (AT1) receptor antagonist that is metabolized to E3174, which is a more potent inhibitor at AT1 receptors than losartan. E3174 is primarily responsible for the antihypertensive activity of losartan. Losartan is metabolized by cytochrome P450 2C9 and 3A4 enzymes to E3174. Rifampin significantly induced the metabolism of losartan and E3174, resulting in a decrease in the area under the concentration-time curve (AUC) and half-life of both compounds.

Severity

Moderate

Onset

Delayed

Evidence

Probable

How To Manage Interaction

In patients receiving losartan and rifampin, monitor blood pressure and adjust the dose of losartan accordingly.

Mechanism Of Interaction

Induction of cytochrome P450 enzymes by rifampin

Literature Reports

A) Ten healthy volunteers received losartan 50 mg daily for seven days, losartan and erythromycin 500 mg four times daily for seven days, and losartan and rifampin 300 mg twice daily for seven days. Each period was separated by a 6-day washout phase. Coadministration of erythromycin with losartan did not significantly affect the AUC, half-life, or oral clearance of losartan and had no effect on the AUC or half-life of E3174. By contrast, rifampin decreased the AUC of losartan and E3174 by 35% (349 ng/hr/mL vs. 225 ng/hr/mL) and 40% (1336 ng/hr/mL vs. 792 ng/hr/mL), respectively. The half-life of both losartan (2 hours vs. 0.9 hours) and E3174 (5.1 hours vs. 2.5 hours) was also decreased by approximately 50% in the presence of rifampin. Erythromycin is a moderate inhibitor of cytochrome P450 3A4 (CYP3A4) enzymes, and rifampin is the most potent inducer of the cytochrome P450 system. Losartan is metabolized by CYP2C9 and CYP3A4 to E3174, and because of the lack of a significant effect caused by erythromycin, it appears that CYP2C9 plays a more prominent role than CYP3A4 in the metabolism of losartan to E3174 .

Losartan Overview

• Losartan is used alone or in combination with other medications to treat high blood pressure. Losartan is also used to decrease the risk of stroke in people who have high blood pressure and a heart condition called left ventricular hypertrophy (enlargement of the walls of the left side of the heart). Losartan may not decrease the risk of stroke in African Americans who have these conditions. This medication is also used to treat kidney disease in people who have type 2 diabetes (condition in which the body does not use insulin normally and therefore cannot control the amount of sugar in the blood) and high blood pressure. Losartan is in a class of medications called angiotensin II receptor antagonists. It works by blocking the action of certain natural substances that tighten the blood vessels, allowing the blood to flow more smoothly and the heart to pump more efficiently.

• 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.

Rifampin Overview

• Rifampin is used with other medications to treat tuberculosis (TB; a serious infection that affects the lungs and sometimes other parts of the body). Rifampin is also used to treat some people who have Neisseria meningitidis (a type of bacteria that can cause a serious infection called meningitis) infections in their noses or throats. These people have not developed symptoms of the disease, and this treatment is used to prevent them from infecting other people. Rifampin should not be used to treat people who have developed symptoms of meningitis. Rifampin is in a class of medications called antimycobacterials. It works by killing the bacteria that cause infection.

• Antibiotics such as rifampin will not work for colds, flu, or other viral infections. Using antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.

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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.