What is the interaction between terbinafine (antifungal) and fluticasone (corticosteroid)?

Terbinafine and Fluticasone Interaction

Terbinafine has minimal drug-drug interactions with fluticasone, making it a safe combination with no significant clinical concerns regarding mortality, morbidity, or quality of life. 1, 2

Mechanism and Safety Profile

Terbinafine, an allylamine antifungal commonly used for onychomycosis, has a favorable drug interaction profile compared to azole antifungals. Unlike azoles (such as itraconazole or fluconazole), terbinafine:

• Primarily interacts only with drugs metabolized by cytochrome P450 2D6 isoenzyme 1
• Does not significantly interact with corticosteroids like fluticasone 2, 3
• Has no contraindications when used with fluticasone 3

Clinical Significance

The lack of interaction between terbinafine and fluticasone is particularly important because:

• Fluticasone is not metabolized through the CYP2D6 pathway that terbinafine affects
• In a large postmarketing surveillance study with over 25,000 patients taking various concomitant medications with terbinafine, no interactions with corticosteroids like fluticasone were identified 3
• Terbinafine has been shown to have fewer clinically significant drug interactions than azole antifungals 4, 3

Important Considerations When Using Terbinafine

While terbinafine can safely be used with fluticasone, clinicians should be aware of:

1. Monitoring requirements:

   • Baseline liver function tests recommended for patients with:
     • History of heavy alcohol consumption
     • Hepatitis
     • Hematological abnormalities 1, 2

2. Side effects to watch for:

   • Gastrointestinal effects (49% of patients) - nausea, diarrhea, taste disturbance
   • Dermatological reactions (23% of patients) - rash, pruritus, urticaria 1, 2
   • Rare but serious reactions including Stevens-Johnson syndrome and hepatotoxicity 2

3. Other drug interactions to avoid:

   • Medications that are CYP2D6 substrates may require monitoring:
     • Certain antidepressants (particularly tricyclics)
     • Some cardiovascular drugs
     • Tamoxifen (combination should be avoided) 5

Clinical Decision Algorithm

1. Assess patient medication profile:

   • If patient is on both terbinafine and fluticasone → No dose adjustment needed
   • If patient is on fluticasone and requires antifungal therapy → Terbinafine is preferred over azoles due to fewer drug interactions

2. Monitor appropriately:

   • No specific monitoring needed for the terbinafine-fluticasone combination
   • Follow standard terbinafine monitoring recommendations (baseline LFTs for high-risk patients)

3. Patient education:

   • Inform about common side effects of terbinafine (not related to the combination)
   • Advise that rare taste disturbance can become permanent 1

Conclusion for Clinical Practice

The combination of terbinafine and fluticasone is safe with no significant interaction concerns. This makes terbinafine the preferred antifungal agent for patients on fluticasone therapy who require systemic antifungal treatment, especially compared to azole antifungals which have more extensive drug interaction profiles 3, 6.