Warfarin with Niacin Interaction Details

Brand Names Associated with Warfarin

Brand Names Associated with Niacin

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Nov 07, 2023

Interaction Effect

Increased risk of bleeding

Interaction Summary

Concomitant use of niacin and warfarin may increase the risk of bleeding. A 69-year-old woman treated with warfarin 2.5 mg/day experienced a critically elevated INR level of 8 after her niacin ER dose was increased to 1000 mg/day. After warfarin holiday, discontinuation of niacin ER, and vitamin K, her INR re-stabilized with warfarin 2.5 mg/day. The mechanism of interaction maybe multifactorial, including niacin-mediated reduction in coagulation factors, decreased CYP450-mediated metabolism of warfarin by niacin metabolites, and saturable first-pass metabolism of niacin. If concomitant therapy is required, more frequent monitoring of INR and/or prothrombin time is recommended, particularly when niacin is initiated or with dosage increase.

Severity

Moderate

Onset

Unspecified

Evidence

Probable

How To Manage Interaction

Concomitant use of niacin and warfarin may increase the risk of bleeding. If concomitant therapy is required, more frequent monitoring of INR and/or prothrombin time is recommended, particularly when niacin is initiated or with dosage increase.

Mechanism Of Interaction

Additive anticoagulation effect and decreased CYP450-mediated metabolism of warfarin by niacin metabolites

Literature Reports

A) A 69-year-old woman treated with warfarin experienced a critically elevated INR after her niacin extended-release (ER) dose was increased. She had a stable INR on warfarin 2.5 mg/day for mechanical aortic valve replacement for over a year. She started niacin ER 500 mg/day about 17 months after warfarin was initiated without changes in INR over 3 months. The dose of niacin ER was increased to 1000 mg/day. One week after niacin ER was increased, her INR increased from 2.4 to 8 (venous INR greater than 12.3). However, she was asymptomatic, she reported no changes in diet or regular medications, and she denied alcohol use, except red wine in the evening. No other abnormal laboratory values were observed. Subsequently, warfarin was held, she received a dose of vitamin K 2.5 mg orally, and she discontinued niacin ER without physician consent. The next day, her INR remained elevated at 10.43 (venous), the warfarin hold was continued, and she received another dose of vitamin K. The following day, her INR was 4.8 and warfarin was resumed at 1 mg alternating with 2 mg for 3 days, with an INR recheck on day 4. Her INR remained in therapeutic range with warfarin 2.5 mg. Causation assessment using the Horn Drug Interaction Probability Scale suggested the interaction was probable .

Warfarin Overview

• Warfarin is used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). Warfarin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.

Niacin Overview

• Niacin is used with diet changes (restriction of cholesterol and fat intake) to reduce the amount of cholesterol (a fat-like substance) and other fatty substances in your blood and to increase the amount of high density lipoprotein (HDL; ''good cholesterol''). Niacin can be used in a number of situations including the following:

  • alone or in combination with other medications, such as HMG-CoA inhibitors (statins) or bile acid-binding resins;

  • to decrease the risk of another heart attack in patients with high cholesterol who have had a heart attack;

  • to prevent worsening of atherosclerosis (buildup of cholesterol and fats along the walls of the blood vessels) in patients with high cholesterol and coronary artery disease;

  • to reduce the amount of triglycerides (other fatty substances) in the blood in patients with very high triglycerides who are at risk of pancreatic disease (conditions affecting the pancreas, a gland that produces fluid to break down food and hormones to control blood sugar).

• Niacin is also used to prevent and treat pellagra (niacin deficiency), a disease caused by inadequate diet and other medical problems. Niacin is a B-complex vitamin. At therapeutic doses, niacin is a cholesterol-lowering medication.

• Results of a clinical study in people with heart disease and well-controlled cholesterol levels that compared people who took niacin and simvastatin with people who took simvastatin alone and found similar results for the two groups in the rate of heart attacks or strokes. Taking niacin along with simvastatin or lovastatin also has not been shown to reduce the risk of heart disease or death compared with the use of niacin, simvastatin, or lovastatin alone. Talk to your doctor if you have questions about the risks and benefits of treating increased amounts of cholesterol in your blood with niacin and other medications.

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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.