What is the recommended use and dosage of Griseofulvin for treating fungal infections?

Griseofulvin for Fungal Infections: Recommended Use and Dosage

Griseofulvin is indicated for the treatment of dermatophyte infections of the skin, hair, and nails that cannot be adequately treated with topical therapy, with dosing based on the specific fungal species involved. 1

Indications

Griseofulvin is FDA-approved for treating the following conditions when caused by susceptible dermatophytes:

• Tinea corporis
• Tinea pedis
• Tinea cruris
• Tinea barbae
• Tinea capitis
• Tinea unguium (onychomycosis)

Important considerations:

• Prior to initiating treatment, laboratory confirmation (KOH preparation, fungal culture, or nail biopsy) should be obtained 1
• Griseofulvin is not effective against bacterial infections, candidiasis, or other non-dermatophyte fungal infections 1
• Not justified for minor dermatophyte infections that will respond to topical agents alone 1

Dosing Recommendations

For Tinea Capitis:

• For patients <50 kg: 15-20 mg/kg/day (single or divided doses) for 6-8 weeks 2
• For patients >50 kg: 1 g/day (single or divided doses) for 6-8 weeks 2
• Higher doses up to 25 mg/kg daily may be necessary for resistant cases 2

For Onychomycosis:

• 1 g daily is most often prescribed (500 mg daily is considered too small a dose) 2
• Treatment duration is typically lengthy (months) 2

Species-Specific Efficacy

Griseofulvin shows variable efficacy depending on the causative organism:

• Microsporum species: Griseofulvin is more effective than terbinafine (88.5% vs 40.8% response rate) 2, 3
• Trichophyton species: Terbinafine is more effective than griseofulvin (94% vs 92% response rate) 3, 4

Administration Tips

• Taking griseofulvin with fatty food increases absorption and improves bioavailability 2, 5
• Griseofulvin is detected in the stratum corneum soon after ingestion, diffusing from extracellular fluid and sweat 5
• For children, the suspension formulation allows more accurate dosage adjustments, though it has become increasingly expensive and less widely available 2

Treatment Duration

• Tinea capitis: 6-8 weeks (standard) 2, 6
• Onychomycosis: 6-18 months (with disappointing results and numerous relapses) 5
• Continue treatment until mycological cure is achieved, not just clinical improvement 6

Adverse Effects and Contraindications

Side Effects:

• Generally well-tolerated, especially in children
• Gastrointestinal disturbances and rashes in <8% of patients
• Very few patients (0.8%) require discontinuation due to side effects 2

Contraindications:

• Lupus erythematosus
• Porphyria
• Severe liver disease 2

Drug Interactions:

• Plasma concentration decreased by rifampicin
• Plasma concentration increased by cimetidine
• Interactions with phenobarbital, anticoagulants, and oral contraceptives 2, 5

Treatment Failure Management

If treatment fails:

1. Consider compliance issues, suboptimal absorption, relative insensitivity of the organism, or reinfection
2. For clinical improvement but ongoing positive mycology: continue current therapy for 2-4 more weeks
3. For no clinical improvement: switch to second-line therapy (terbinafine for Trichophyton infections or itraconazole) 2

Comparison with Other Antifungals

• Terbinafine: More effective for Trichophyton species, requires shorter treatment duration (2-4 weeks), but less effective for Microsporum species 2, 3
• Itraconazole: Effective against both Trichophyton and Microsporum species, used as second-line therapy 2
• Fluconazole: Reserved for exceptional circumstances 6

While newer antifungals like terbinafine may offer advantages such as shorter treatment duration, griseofulvin remains the only FDA-approved treatment for tinea capitis in children in the US and has decades of established safety data 2, 7.