Griseofulvin Dosing for Tinea Corporis of the Face
For this 12-year-old child weighing 40 kg with tinea corporis of the face, administer griseofulvin 600-800 mg per day (15-20 mg/kg/day) given as a single dose or divided doses for 4-6 weeks, taken with fatty food to enhance absorption. 1
Dosing Rationale
The British Association of Dermatologists guidelines provide clear weight-based dosing for children under 50 kg: 15-20 mg/kg/day for 6-8 weeks 1. However, these guidelines specifically address tinea capitis (scalp infections), which typically require longer treatment durations than tinea corporis.
For your 40 kg patient:
- Minimum dose: 15 mg/kg × 40 kg = 600 mg/day
- Standard dose: 20 mg/kg × 40 kg = 800 mg/day
- Duration: 4-6 weeks (shorter than tinea capitis)
Key Administration Points
- Give with fatty food to significantly increase absorption and bioavailability 1, 2
- Can be administered as a single daily dose or divided into two doses 1
- The drug can be given in tablet form at this age and weight
Important Clinical Considerations
Species Matters
While you haven't identified the causative organism, griseofulvin demonstrates 88.5% response rates for Microsporum species but only 67.9% for Trichophyton species 1. If possible, obtain fungal culture to guide therapy, though empirical treatment is reasonable given typical clinical features 1.
Resistant Cases
If there is no clinical improvement after 4 weeks, consider:
- Increasing the dose up to 25 mg/kg/day (1000 mg/day for this patient) 1
- Extending treatment duration to 8 weeks
- Switching to alternative therapy if no response 1
Contraindications to Avoid
Do not use griseofulvin if the patient has:
- Lupus erythematosus
- Porphyria
- Severe liver disease 1
Drug Interactions
- Rifampicin decreases griseofulvin plasma concentrations
- Cimetidine increases griseofulvin plasma concentrations 1
Monitoring and Follow-up
The endpoint should be mycological cure, not just clinical improvement 1. Consider repeat mycology sampling if lesions persist beyond expected treatment duration. Side effects are generally minor in children (headaches, gastrointestinal symptoms, rashes in <8%) with very few requiring discontinuation 1, 3.