Griseofulvin for Dermatophyte Infections
Griseofulvin is the first-line oral antifungal specifically for Microsporum species infections (particularly tinea capitis), dosed at 15-20 mg/kg/day for 6-8 weeks in patients <50 kg or 1 g/day for those >50 kg, and remains the only licensed treatment for tinea capitis in children in the U.K. 1
Primary Indications
Griseofulvin is indicated for dermatophyte infections of skin, hair, and nails that are not adequately treated by topical therapy alone 2. The drug demonstrates species-specific efficacy, being particularly effective against:
- Microsporum species (M. canis, M. audouinii) - 88.5% response rate 1
- Trichophyton species - 67.9% response rate (requires longer treatment) 1
Key clinical point: Choose griseofulvin over terbinafine when Microsporum species are suspected or confirmed, as terbinafine shows poor efficacy against these organisms 1.
Dosing Regimen
Weight-Based Dosing 1:
- <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
Resistant Cases:
Administration Instructions
Critical for absorption: Administer with fatty food to significantly enhance bioavailability 1, 2. In pediatric patients, giving griseofulvin with milk resulted in 4-fold higher peak serum concentrations and 10-fold greater area under the curve compared to fasting administration 2.
Available formulations include micronized, ultramicronized, and suspension forms, though the suspension is no longer licensed in the U.K. 1
Absolute Contraindications 1:
- Lupus erythematosus
- Porphyria
- Severe liver disease
Drug Interactions
Decreased griseofulvin levels 1:
- Rifampicin (avoid combination)
Increased griseofulvin levels 1:
- Cimetidine
Griseofulvin decreases efficacy of 3:
- Oral contraceptives (counsel patients on backup contraception)
- Warfarin (monitor INR closely)
- Phenobarbital interactions reported
Monitoring Requirements
The endpoint is mycological cure, not just clinical improvement 1. This is a critical pitfall—patients may appear clinically better while still harboring fungal elements.
Monitoring Protocol:
- Repeat mycology sampling until mycological clearance is achieved 1
- If clinical improvement but ongoing positive mycology: continue therapy for additional 2-4 weeks 1
- If no initial clinical improvement: switch to second-line therapy 1
Treatment Failure Considerations 1:
- Non-compliance (prolonged 6-8 week course affects adherence)
- Suboptimal drug absorption (ensure taking with fatty food)
- Relative organism insensitivity
- Reinfection
Safety Profile
Griseofulvin is well-tolerated, particularly in children 1:
- Minor side effects in <8%: gastrointestinal disturbances, rashes, headaches
- Only 0.8% require discontinuation 1
- Over 50 years of clinical experience 1
Clinical Pearls
When to start treatment: In the presence of kerion or cardinal signs (scale, lymphadenopathy, alopecia), it is reasonable to start treatment before mycology confirmation 1.
Adjunctive topical therapy: While topical therapy alone is insufficient, adding antifungal shampoos (ketoconazole 2%, selenium sulfide 1%, or povidone-iodine) reduces spore transmission 1.
School attendance: Children on appropriate systemic therapy should be allowed to attend school or nursery 1.
Family screening: For T. tonsurans infections, screen all family members and close contacts, treating positive cases 1.
Common Pitfalls to Avoid
- Using griseofulvin for Trichophyton species as first-line: Terbinafine is superior for these organisms 1
- Stopping at clinical cure: Always confirm mycological clearance 1
- Not administering with fatty food: This significantly reduces absorption 1, 2
- Inadequate treatment duration: Microsporum requires full 6-8 weeks; Trichophyton may need 12-18 weeks 1