What are the dosing recommendations for terbinafine and griseofulvin in a pediatric patient with tinea capitis?

Dosing for Terbinafine and Griseofulvin in Pediatric Tinea Capitis

The choice between terbinafine and griseofulvin depends on the causative organism: use terbinafine for Trichophyton species infections and griseofulvin for Microsporum species infections, with specific weight-based dosing protocols for each. 1

Species-Directed Treatment Algorithm

For Trichophyton Species (T. tonsurans, T. violaceum, T. soudanense)

Terbinafine is the preferred agent 1

Weight-based dosing:

• < 20 kg: 62.5 mg per day for 2-4 weeks 1
• 20-40 kg: 125 mg per day for 2-4 weeks 1
• > 40 kg: 250 mg per day for 2-4 weeks 1

For Microsporum Species (M. canis, M. audouinii)

Griseofulvin is the preferred agent 1

Weight-based dosing:

• < 50 kg: 15-20 mg/kg per day (single or divided dose) for 6-8 weeks 1
• > 50 kg: 1 g per day (single or divided dose) for 6-8 weeks 1

Critical Dosing Considerations

Griseofulvin Optimization

• Higher doses (20-25 mg/kg/day) may be required for Trichophyton infections, with treatment extended to 12-18 weeks in resistant cases 1
• Administer with fatty food to increase absorption and improve bioavailability 1
• The standard FDA-approved pediatric dose is 10 mg/kg daily, but clinical practice often requires higher dosing 2
• Griseofulvin remains the only licensed treatment for tinea capitis in children in the UK, though terbinafine is widely used off-label 1

Terbinafine Efficacy Patterns

• Terbinafine achieves significantly higher cure rates than griseofulvin for Trichophyton species (mycologic cure 61.5% vs 55.5%, complete cure 45.1% vs 39.2%) 3
• For Microsporum canis, griseofulvin is significantly more effective than terbinafine because terbinafine cannot be incorporated into hair shafts in prepubertal children and doesn't reach the scalp surface where Microsporum arthroconidia are located 1
• 8 weeks of griseofulvin is significantly more effective than 4 weeks of terbinafine for confirmed Microsporum infection 1

Common Pitfalls to Avoid

Treatment Duration Errors

• Do not shorten terbinafine treatment to less than 2 weeks - shorter courses (1 week) result in significantly lower cure rates 4
• Do not extend terbinafine treatment beyond 4 weeks - prolonging treatment does not improve efficacy 1
• For griseofulvin, ensure full 6-8 week course for Microsporum species to achieve adequate cure rates 1

Species-Specific Mistakes

• Do not use terbinafine as first-line for Microsporum canis - it has poor efficacy due to pharmacokinetic limitations in prepubertal children 1
• Obtain fungal culture before treatment when possible to guide species-directed therapy, though empiric treatment is reasonable with clinical signs (scale, lymphadenopathy, alopecia) 1

Safety Profile

Terbinafine

• Well tolerated with gastrointestinal disturbances and rashes in < 8% of patients 1
• Only 0.8% require discontinuation 1
• No significant effects on liver transaminases in short-term use 3

Griseofulvin

• Contraindicated in lupus erythematosus, porphyria, and severe liver disease 1
• Plasma concentration decreased by rifampicin and increased by cimetidine 1
• Gastrointestinal effects reported in approximately 12% of patients 5

Treatment Failure Management

If no clinical improvement after initial treatment course:

• Consider lack of compliance, suboptimal drug absorption, or organism insensitivity 1
• If clinical improvement but ongoing positive mycology: continue current therapy for additional 2-4 weeks 1
• If no initial clinical improvement: switch to second-line therapy with itraconazole (5 mg/kg per day for 2-4 weeks) 1

For Trichophyton treatment failures on griseofulvin: switch to terbinafine at standard dosing 1

For Microsporum treatment failures on terbinafine: switch to griseofulvin at standard dosing 1