No Clinically Significant Drug Interaction Between Augmentin and Terbinafine
Augmentin (amoxicillin-clavulanate) and terbinafine do not have a clinically significant drug interaction and can be safely co-administered without dose adjustments or special monitoring beyond standard care.
Pharmacologic Basis for Safety
Terbinafine's Minimal Interaction Profile
According to the British Association of Dermatologists guidelines, oral terbinafine has minimal drug-drug interactions 1. The only potentially significant drug interaction with terbinafine involves drugs metabolized by the cytochrome P450 2D6 isoenzyme 1.
The FDA drug label confirms that terbinafine:
- Is a CYP2D6 inhibitor
- Does not inhibit metabolism of multiple other drugs in vitro studies
- Has no effect on clearance of antipyrine or digoxin 2
Amoxicillin-Clavulanate Metabolism
Amoxicillin-clavulanate is not metabolized through the CYP2D6 pathway. Beta-lactam antibiotics like amoxicillin are primarily eliminated renally, and clavulanic acid undergoes minimal hepatic metabolism through different pathways than those affected by terbinafine.
Documented Interaction Profile
The FDA label for terbinafine specifically states: "The influence of terbinafine on the pharmacokinetics of fluconazole, cotrimoxazole (trimethoprim, sulfamethoxazole), zidovudine or theophylline was not considered to be clinically significant" 2. While amoxicillin-clavulanate is not explicitly listed, this demonstrates terbinafine's lack of interaction with other antimicrobials.
A comprehensive review noted that terbinafine has been responsible for fewer clinically significant drug interactions than triazole antifungals, with no drug-drug contraindications identified 3. In a large postmarketing surveillance study of 25,884 patients, 42.8% were taking concomitant medications, and no new drug-drug interactions were revealed 3.
Clinical Implications
Safe Co-Administration
- No dose adjustments needed for either medication
- No additional monitoring required beyond standard care for each drug individually
- No contraindication to concurrent use
Standard Monitoring Remains Appropriate
For terbinafine: Baseline liver function tests and complete blood count in patients with history of hepatotoxicity or hematological abnormalities 1
For amoxicillin-clavulanate: Standard monitoring for antibiotic therapy (clinical response, adverse effects)
Important Caveat: Warfarin Consideration
If the patient is also taking warfarin, be aware that:
- Both terbinafine and amoxicillin-clavulanate can independently affect INR 2
- Terbinafine: Spontaneous reports of altered prothrombin times (both increases and decreases) 2
- Amoxicillin-clavulanate: Can elevate INR, particularly at higher doses (10-12 g/day) 4
- Action required: More frequent INR monitoring if patient is on warfarin with either or both medications
However, this warfarin interaction is not an interaction between terbinafine and amoxicillin-clavulanate themselves—rather, each drug independently affects warfarin metabolism.
Bottom Line
The combination of Augmentin and terbinafine is safe without special precautions. The drugs work through different mechanisms, are metabolized via different pathways, and have no documented pharmacokinetic or pharmacodynamic interactions with each other.