What are the potential interactions between terbinafine and other medications?

From the Guidelines

Terbinafine has minimal drug–drug interactions, but caution is advised when co-administering with CYP2D6 inhibitors, such as fluoxetine, paroxetine, and quinidine, as terbinafine may increase blood levels of these drugs. When considering the potential interactions between terbinafine and other medications, it is essential to prioritize the patient's safety and well-being.

• The most significant interactions occur with CYP2D6 inhibitors, which can lead to increased blood levels of these drugs, potentially causing adverse effects.
• Cimetidine can decrease terbinafine clearance by 33%, while rifampin may increase it by 100%, affecting terbinafine's effectiveness 1.
• Patients taking medications metabolized by CYP2D6, including certain antidepressants, beta-blockers, antipsychotics, and antiarrhythmics, should be monitored for increased side effects.
• Those with liver disease should use terbinafine cautiously, as it's primarily metabolized by the liver.
• Always inform your healthcare provider about all medications you're taking, including over-the-counter drugs and supplements, before starting terbinafine treatment.
• The evidence suggests that terbinafine is generally well tolerated, but rare reports of serious adverse reactions, including Stevens–Johnson syndrome and toxic epidermal necrolysis, have been reported 1.
• The British Association of Dermatologists' guidelines for the management of onychomycosis 2014 recommend baseline liver function tests and a complete full blood count in patients with a history of heavy alcohol consumption, hepatitis, or haematological abnormalities 1.
• Additionally, the guidelines suggest that terbinafine is not recommended in patients with active or chronic liver disease 1.
• In terms of specific interactions, itraconazole has been reported to have enhanced toxicity with certain medications, including warfarin, some anti-histamines, antipsychotics, anxiolytics, digoxin, cisapride, ciclosporin, and simvastatin 1.
• However, the most recent and highest quality study, the British Association of Dermatologists' guidelines for the management of onychomycosis 2014, provides the most relevant information on terbinafine interactions 1.

From the FDA Drug Label

Terbinafine is an inhibitor of CYP450 2D6 isozyme and has an effect on metabolism of desipramine. Drug interactions have also been noted with cimetidine, fluconazole, cyclosporine, rifampin, and caffeine. (7.1)

The potential interactions between terbinafine and other medications include:

• Inhibition of CYP450 2D6 isozyme: affecting the metabolism of desipramine 2
• Interactions with:
  • Cimetidine
  • Fluconazole
  • Cyclosporine
  • Rifampin
  • Caffeine 2, 2

From the Research

Potential Interactions between Terbinafine and Other Medications

• Terbinafine is an antifungal medication that can interact with other drugs, including cyclosporin 3
• The interaction between terbinafine and cyclosporin is less significant compared to other antifungal medications such as ketoconazole, itraconazole, and fluconazole 3
• Terbinafine has been shown to have a low potential for interaction with cyclosporin, with an IC50 value above 100 microM 3
• In contrast, ketoconazole is a potent inhibitor of cyclosporin metabolism, with an IC50 value of 0.24 +/- 0.01 microM 3
• Itraconazole and fluconazole also have the potential to interact with cyclosporin, although to a lesser extent than ketoconazole 3

Hepatic Reactions and Drug Interactions

• Terbinafine can cause hepatic reactions, including reversible hepatic damage 4, 5, 6
• Patients taking terbinafine should be advised to inform their physician if they experience any warning symptoms of hepatic damage 4
• The risk of hepatic reactions with terbinafine is low, but patients should be monitored for signs of liver injury 5, 6
• Terbinafine-induced liver injury is a rare but potentially serious side effect of the medication 6

Clinical Relevance of Drug Interactions

• The interaction between terbinafine and other medications can have clinical significance, particularly in patients taking cyclosporin 3
• Patients taking terbinafine and cyclosporin concurrently should be monitored for signs of interaction, including increased cyclosporin levels 3
• The decision to use terbinafine in patients taking other medications should be made on a case-by-case basis, taking into account the potential risks and benefits of the interaction 7