Are there contraindications for using long-term Terbinifine (Terbinafine) in patients with a history of coagulopathy (clotting disorders), thrombosis (blood clots), atrial fibrillation (a fib), or those taking chronic anticoagulants (blood thinners)?

From the Guidelines

Terbinafine can be used in patients with a history of coagulopathy, thrombosis, atrial fibrillation, or those taking chronic anticoagulants, but caution and close monitoring are advised due to potential interactions and rare adverse effects. The primary concerns with terbinafine relate to its potential hepatotoxicity and rare hematologic effects rather than direct interactions with clotting mechanisms, as noted in the British Association of Dermatologists' guidelines for the management of onychomycosis 1. Patients on blood thinners like warfarin should be monitored more closely as terbinafine may slightly alter the metabolism of some anticoagulants through cytochrome P450 interactions, potentially affecting INR values.

Some key points to consider when using terbinafine in these patients include:

• Baseline liver function tests should be performed before starting long-term terbinafine, with periodic monitoring during treatment, especially in patients with a history of heavy alcohol consumption, hepatitis, or hematological abnormalities 1.
• The potential for rare but serious adverse reactions, such as Stevens-Johnson syndrome, toxic epidermal necrolysis, and hepatic toxicity, should be considered, particularly in patients with pre-existing liver disease 1.
• Terbinafine has minimal drug-drug interactions, but the potential interaction with drugs metabolized by the cytochrome P450 2D6 isoenzyme should be considered, and patients on anticoagulants should be monitored closely for changes in INR values.
• While terbinafine has been rarely associated with blood dyscrasias like neutropenia and thrombocytopenia, there is no strong evidence suggesting it directly worsens clotting disorders or increases thrombotic risk, as per the guidelines 1.

The decision to use terbinafine in patients with clotting disorders, history of blood clots, atrial fibrillation, or those on chronic anticoagulants should involve weighing the benefits of treating the fungal infection against potential risks, with appropriate monitoring of both liver function and anticoagulation parameters throughout treatment, as suggested by the available evidence 1.

From the Research

Contraindications for Long-term Terbinafine Use

• There are potential contraindications for using long-term Terbinafine in patients with a history of coagulopathy, thrombosis, atrial fibrillation, or those taking chronic anticoagulants, as evidenced by a case report of an 88-year-old male patient who experienced a low-efficient INR level after initiation of terbinafine while being anticoagulated with warfarin due to atrial fibrillation 2.
• The interaction between warfarin and terbinafine can have serious consequences in many clinical situations for which anticoagulation therapy with warfarin is indicated, suggesting that combined therapy with warfarin and oral terbinafine should be used with caution 2.
• Patients with heart failure and atrial fibrillation are at increased risk of bleeding when taking direct oral anticoagulants (DOACs), and renal function decline can result in increased bleeding in patients with DOACs, highlighting the need for closer monitoring in these patients 3.
• The risk of stroke in patients with atrial fibrillation can be reduced with anticoagulation therapy, and the decision to anticoagulate patients with atrial fibrillation involves weighing the risk of an embolic event without therapy versus the risk of a hemorrhagic event on therapy 4.
• Anaemia is associated with an increased risk of bleeding and thrombotic complications in patients with atrial fibrillation treated with warfarin, and repeated low haemoglobin results can refer to suboptimal management and increased complication risk in anticoagulated patients 5.
• Novel oral anticoagulants (NOACs) have advantages over warfarin in patients with atrial fibrillation, but there is no strong evidence that they should replace warfarin or low-molecular-weight heparin in primary prevention, treatment, or secondary prevention of venous thromboembolism 6.

Considerations for Patients with Atrial Fibrillation

• Patients with atrial fibrillation associated with rheumatic valvular disease, prosthetic valve disease, or nonvalvular atrial fibrillation may benefit from anticoagulation therapy to reduce the risk of stroke 4.
• The risk of embolic events in patients with atrial fibrillation can be assessed based on factors such as hypertension, previous embolic events, structural heart disease, and older age 4.
• Patients with atrial fibrillation and anaemia are at increased risk of bleeding and thrombotic complications, and repeated low haemoglobin results can refer to suboptimal management and increased complication risk in anticoagulated patients 5.

Interactions between Terbinafine and Anticoagulants

• The interaction between warfarin and terbinafine can lead to an increased pharmacological effect of warfarin, resulting in a low-efficient INR level and increased risk of bleeding 2.
• The concomitant use of terbinafine and anticoagulants such as warfarin or DOACs requires careful monitoring of INR levels and bleeding risk to minimize the risk of adverse events 2, 3.