GRISEOFULVIN, ULTRAMICROSIZE
Clinical safety rating: avoid
Warfarin metabolism is decreased increasing INR Can cause photosensitivity and lupus-like syndrome.
Binds to tubulin, disrupting microtubule function and inhibiting fungal cell mitosis; deposited in keratin precursor cells, making keratin resistant to fungal invasion.
| Metabolism | Hepatic metabolism via CYP450 (demethylation and conjugation); metabolites are inactive. |
| Excretion | Renal (<1% unchanged); fecal (36% as metabolites); tissue deposition may persist for weeks. |
| Half-life | 9-24 hours (mean 15 hours); prolonged in liver disease. |
| Protein binding | 84% bound to albumin. |
| Volume of Distribution | 1.5-2 L/kg; indicates extensive tissue distribution, especially skin, hair, nails, and liver. |
| Bioavailability | Ultramicrosize formulation: approximately 95% absorbed (compared to 25-70% for microsize). |
| Onset of Action | 48-72 hours for serum levels to reach therapeutic range; clinical improvement in tinea infections typically seen within 2-4 weeks. |
| Duration of Action | Therapeutic effect persists for weeks after cessation due to deposition in keratin precursor cells. |
250-375 mg orally once daily or 500-750 mg orally once daily for severe infections.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for renal impairment. |
| Liver impairment | Contraindicated in severe hepatic disease. For Child-Pugh A or B, use with caution and monitor liver function; no specific dose adjustment established. |
| Pediatric use | 10-20 mg/kg/day orally as a single dose or divided twice daily; maximum 750 mg/day. |
| Geriatric use | Use with caution due to potential age-related hepatic impairment; no specific dose adjustment recommended, but monitor for adverse effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Warfarin metabolism is decreased increasing INR Can cause photosensitivity and lupus-like syndrome.
| FDA category | Contraindicated |
| Breastfeeding | Contraindicated in breastfeeding due to excretion into breast milk and potential for hepatic toxicity and carcinogenicity in the infant. M/P ratio unknown. Discontinue nursing or drug. |
| Teratogenic Risk | GRISEOFULVIN, ULTRAMICROSIZE is contraindicated in pregnancy. First trimester: known teratogen with increased risk of fetal malformations including conjoined twins and central nervous system defects. Second and third trimesters: avoid; potential for fetal toxicity based on animal studies. No human data available. |
■ FDA Black Box Warning
No black box warning.
| Common Effects | Application site reactions burning irritation itching and redness Skin peeling Headache Diarrhea Rash Indigestion Abnormal liver enzyme Itching Taste change Nausea Abdominal pain Flatulence |
| Serious Effects |
["Porphyria","Hepatic failure","Hypersensitivity to griseofulvin","Lupus erythematosus (relative)","Pregnancy (category C; teratogenic in animals)"]
| Precautions | ["Hepatotoxicity (monitor liver function)","Hypersensitivity reactions","Lupus-like syndrome exacerbation","Photosensitivity","Carcinogenic in animal studies (avoid prolonged use)","Monitor blood dyscrasias (rare)"] |
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| Fetal Monitoring | Monitor hepatic function tests (AST, ALT, bilirubin) and complete blood count periodically during therapy. Assess for signs of hypersensitivity reactions. Fetal monitoring via ultrasound if inadvertent exposure during pregnancy. |
| Fertility Effects | Animal studies show reduced spermatogenesis and testicular degeneration in males; reversible after discontinuation. No human studies on fertility effects. May impair fertility in both sexes. |