What are the differences in treatment and dosage between Terbinafine (terbinafine) and Griseofulvin (griseofulvin) for fungal infections?

Terbinafine vs Griseofulvin for Fungal Infections: Treatment and Dosage Differences

Terbinafine should be used as first-line treatment for Trichophyton species infections, while griseofulvin is more effective for Microsporum species infections, with treatment selection guided by the causative dermatophyte species. 1

Mechanism of Action and Spectrum

• Terbinafine:

  • Allylamine antifungal with fungicidal action
  • Acts by inhibiting squalene epoxidase, essential for fungal cell wall synthesis
  • Higher efficacy against Trichophyton species
  • Less effective against Microsporum species
  • Shows excellent activity against dermatophytes but less activity against yeasts 1, 2

• Griseofulvin:

  • Fungistatic action
  • More effective against Microsporum species (88.5% response rate)
  • Less effective against Trichophyton species (67.9% response rate)
  • No evidence of resistance in vitro, but clinically less effective against Trichophyton 1

Dosage Recommendations

Terbinafine Dosing

For tinea capitis (by weight):

• <20 kg: 62.5 mg daily for 2-4 weeks
• 20-40 kg: 125 mg daily for 2-4 weeks

• 40 kg: 250 mg daily for 2-4 weeks 1

For onychomycosis:

• Adults: 250 mg once daily for 6 weeks (fingernails) or 12 weeks (toenails) 3
• Children: Weight-based dosing for 6 weeks (fingernails) or 12 weeks (toenails) 3

Griseofulvin Dosing

For tinea capitis (by weight):

• <50 kg: 15-20 mg/kg/day (single or divided dose) for 6-8 weeks

• 50 kg: 1 g/day (single or divided dose) for 6-8 weeks 1

For onychomycosis:

• 500-1000 mg daily for 12-18 months for toenail infections 3
• Pediatric dosage: 10 mg/kg daily (specifically licensed for children) 3

Treatment Duration

• Terbinafine:

  • Shorter treatment duration (2-4 weeks for tinea capitis, 6-12 weeks for onychomycosis)
  • May improve compliance due to shorter course 1, 3

• Griseofulvin:

  • Longer treatment duration (6-8 weeks for tinea capitis, 12-18 months for onychomycosis)
  • Prolonged treatment may affect compliance 1, 3

Efficacy Comparison

A meta-analysis of randomized controlled trials demonstrated:

• Terbinafine is more efficacious than griseofulvin for Trichophyton species infections (OR 1.616,95% CI 1.274-2.051, p<0.001)
• Griseofulvin is more efficacious than terbinafine for Microsporum species infections (OR 0.408,95% CI 0.254-0.656, p<0.001) 4

For onychomycosis, terbinafine showed superior long-term efficacy compared to griseofulvin:

• At 48 weeks follow-up: 60% cure rate with terbinafine vs 39% with griseofulvin (p=0.006)
• Mycological cure: 81% with terbinafine vs 62% with griseofulvin (p=0.02) 5

Side Effects and Contraindications

• Terbinafine:

  • Generally well-tolerated in children
  • Side effects include gastrointestinal disturbances and rashes (<8%)
  • Very few patients (0.8%) require discontinuation 1
  • Contraindicated in severe hepatic impairment 3

• Griseofulvin:

  • Contraindications: Lupus erythematosus, porphyria, severe liver disease
  • Drug interactions: Plasma concentration decreased by rifampicin and increased by cimetidine 1

Treatment Algorithm

1. Identify causative organism through microscopy and culture
2. Select antifungal based on species:
   • For Trichophyton species: Terbinafine first-line
   • For Microsporum species: Griseofulvin first-line
3. Consider patient factors:
   • Age (griseofulvin is specifically licensed for children)
   • Liver function (avoid both in severe hepatic impairment)
   • Potential drug interactions
   • Compliance (shorter course with terbinafine may be advantageous)
4. Monitor for treatment failure:
   • If clinical improvement but ongoing positive mycology: continue current therapy for 2-4 weeks
   • If no clinical improvement: switch to alternative agent 1

Important Clinical Considerations

• Baseline liver function tests and complete blood count are recommended for patients taking terbinafine 3
• Topical therapy alone is not recommended for tinea capitis; oral therapy is generally indicated 1
• For treatment failures, consider lack of compliance, poor absorption, relative insensitivity of the organism, or reinfection 1
• The end point of treatment should be mycological rather than clinical cure 1