Griseofulvin Dosing: 1000mg vs 920mg
Yes, you can take 1000mg of griseofulvin instead of 920mg—in fact, 1000mg (1g) daily is the most commonly prescribed dose for adults with nail infections, as 500mg daily is generally recognized as too small a dose for onychomycosis. 1
Standard Adult Dosing
The evidence clearly supports higher dosing for fungal infections:
For onychomycosis (nail infections): The recommended adult dose is 500-1000mg per day, with 1g daily being most often prescribed for nail infections, though there is no certain evidence that this improves cure rates in toenail infection compared to lower doses. 1
Treatment duration: 6-9 months for fingernail infections and 12-18 months for toenail infections. 1, 2
For tinea capitis (scalp infections) in adults >50kg: 1g/day in single or divided doses for 6-8 weeks. 2
Important Dosing Considerations
Absorption enhancement: Take griseofulvin with fatty food to increase absorption and improve bioavailability. 1, 2
Resistant cases: Doses up to 25mg/kg/day may be necessary for more prolonged periods in resistant cases. 1, 2
Critical Limitations of Griseofulvin
You should be aware that griseofulvin has significant limitations:
Poor efficacy for nail infections: Mycological cure rates for toenail onychomycosis are only 30-40%, with high relapse rates. 1
Newer agents are superior: Both terbinafine and itraconazole have demonstrated significantly higher cure rates than griseofulvin for dermatophyte onychomycosis and are now considered treatments of choice. 1
Long treatment duration required: The lengthy treatment necessary (12-18 months for toenails) affects compliance and cost-effectiveness despite the drug's low price. 1
Safety Monitoring
Contraindications: Griseofulvin is contraindicated in pregnancy (may cause fetal harm including conjoined twins), porphyria, lupus erythematosus, and severe liver disease. 1, 3
Common side effects: Gastrointestinal disturbances, headaches, and rashes occur in 8-15% of patients. 1, 4
Drug interactions: Plasma concentration is decreased by rifampicin and increased by cimetidine; it also interacts with warfarin, ciclosporin, and oral contraceptive pills (may reduce contraceptive efficacy). 1, 2
Clinical Recommendation
The 80mg difference between 920mg and 1000mg is clinically insignificant and falls well within the standard dosing range. However, given griseofulvin's poor cure rates for nail infections, you should discuss with your prescriber whether switching to terbinafine (which has fungicidal rather than fungistatic activity and much higher cure rates) would be more appropriate for your condition. 1