What is the recommended dosage and treatment duration for Griseofulvin (antifungal medication) in adults and children for dermatophyte infections?

Griseofulvin Use and Dosage

Griseofulvin is no longer the treatment of choice for dermatophyte infections due to poor cure rates and high relapse rates, but remains the only licensed systemic antifungal for pediatric onychomycosis and is still effective for tinea capitis caused by Microsporum species. 1

Adult Dosing

Onychomycosis (Nail Infections)

• Dose: 500-1000 mg daily (1 g daily most commonly prescribed) 1, 2
• Duration:
  • Fingernails: 6-9 months 1
  • Toenails: 12-18 months 1
• Administration: Must be taken with fatty food to increase absorption 1, 2, 3
• Strength of recommendation: C (lower efficacy compared to terbinafine and itraconazole) 1

Tinea Capitis (Scalp Ringworm)

• Dose: 1 g/day in single or divided doses for patients >50 kg 2
• Duration: 6-8 weeks 2
• Note: Griseofulvin shows 88.5% response rates for Microsporum species but only 67.9% for Trichophyton species 2

Pediatric Dosing

Standard Dosing (Age 1 month and above)

• Dose: 10 mg/kg per day (maximum 500 mg) 1
• Alternative dosing for tinea capitis: 15-20 mg/kg/day 4
• Duration: 6-8 weeks for tinea capitis 4, 5
• Administration: Take with fatty food to enhance absorption 1, 3
• Strength of recommendation: 1 (second-line if terbinafine/itraconazole contraindicated or not tolerated) 1

Resistant Cases

• Dose: Up to 25 mg/kg/day may be necessary for prolonged periods 2

Critical Limitations and Why It's Not First-Line

Griseofulvin has significantly inferior efficacy compared to newer agents:

• Mycological cure rates for toenail onychomycosis: only 30-40% 2
• High relapse rates after treatment completion 1, 2
• Terbinafine achieves 76% complete cure vs. 39% with griseofulvin in fingernail infections 6
• Lengthy treatment duration (12-18 months for toenails) affects compliance 1, 2

Contraindications

Absolute contraindications: 1, 2

• Pregnancy (manufacturers caution against men fathering children for 6 months after therapy) 1
• Porphyria 1, 2
• Lupus erythematosus 1, 2
• Severe liver disease 1, 2

Common Adverse Effects

• Nausea and rashes occur in 8-15% of patients 1
• Headaches and gastrointestinal disturbances 1, 2
• Generally well-tolerated, particularly in children 4

Drug Interactions

Significant interactions requiring monitoring: 1, 2

• Warfarin (decreased anticoagulant effect)
• Ciclosporin (decreased levels)
• Oral contraceptive pills (decreased efficacy)
• Rifampicin (decreases griseofulvin levels)
• Cimetidine (increases griseofulvin levels)

Pharmacokinetic Considerations

• Peak serum levels occur 4 hours after oral administration 3, 4
• Absorption varies considerably (27-72%) due to poor aqueous solubility 3
• In pediatric patients, administration with milk results in 4-fold higher peak concentrations and 10-fold larger area under the curve 3
• Half-life: 9-24 hours 3
• Approximately 30% excreted in urine within 24 hours, mostly as metabolites 3

When to Consider Griseofulvin

Appropriate clinical scenarios:

• Pediatric onychomycosis when terbinafine/itraconazole are contraindicated (only licensed option for children) 1
• Tinea capitis caused by Microsporum species (superior to terbinafine for this organism) 7, 2
• Cost constraints in non-nail dermatophyte infections 1
• Patients unable to tolerate terbinafine or azole antifungals 1

Clinical pitfall: Despite low drug cost, poor cure rates often necessitate retreatment, resulting in a relatively high cost-to-efficacy ratio 1