What is the recommended dosing for terbinafine (Lamisil) in adults with normal and impaired renal function?

Terbinafine Dosing Recommendations

The recommended dosing for terbinafine (Lamisil) in adults is 250 mg once daily for 6 weeks in fingernail infections and 12-16 weeks in toenail infections. 1

Adult Dosing Guidelines

Standard Dosing

• Fingernail infections: 250 mg once daily for 6 weeks
• Toenail infections: 250 mg once daily for 12-16 weeks 1

Monitoring Requirements

• Baseline liver function tests and complete blood count recommended for:
  • Patients with history of hepatotoxicity
  • Patients with history of hematological abnormalities
  • Patients receiving concomitant hepatotoxic medications 1

Special Populations

Renal Impairment

• Terbinafine is contraindicated in severe renal impairment 1
• For moderate to severe renal impairment (creatinine clearance <50 mL/min), dose should be reduced by 50% (125 mg daily) 2

Hepatic Impairment

• Terbinafine is not recommended in patients with active or chronic liver disease 1
• Contraindicated in severe hepatic impairment 1

Treatment Duration Considerations

The British Association of Dermatologists guidelines indicate that treatment duration should be based on the location and severity of infection:

• Shorter treatment durations (6 weeks) for fingernail infections are sufficient due to faster nail growth rates 1, 3
• Longer treatment durations (12-16 weeks) are necessary for toenail infections to achieve optimal cure rates 1, 3

Research has demonstrated that attempting to shorten the treatment duration for toenail infections to 6 weeks results in significantly lower mycological cure rates (59.7%) compared to the standard 12-week regimen (72.4%) 4.

Efficacy and Comparative Effectiveness

Terbinafine has demonstrated superior efficacy compared to other antifungals:

• Higher mycological cure rates than itraconazole (76% vs 38% after 12 weeks) 5
• Lower relapse rates than itraconazole (23% vs 53%) in long-term follow-up studies 1, 5
• More effective than griseofulvin and fluconazole for dermatophyte onychomycosis 1, 6

Common Pitfalls and Caveats

1. Inadequate treatment duration: Attempting to shorten therapy for toenail infections often leads to treatment failure and relapse 4

2. Drug interactions: Unlike azoles, terbinafine has minimal drug-drug interactions, but can interact with drugs metabolized by cytochrome P450 2D6 isoenzyme 1

3. Adverse effects monitoring: Watch for:

   • Taste disturbance (rare but can be permanent)
   • Gastrointestinal upset
   • Headache
   • Potential exacerbation of psoriasis
   • Subacute lupus-like syndrome 1

4. Follow-up evaluation: Patients should be re-evaluated 3-6 months after treatment initiation to assess response and determine if additional treatment is needed 1

Terbinafine remains the first-line treatment for dermatophyte onychomycosis due to its superior efficacy, favorable safety profile, and relatively low potential for drug interactions 1, 5, 6.