Griseofulvin is a classic oral antifungal for hair, skin and nail tineas, especially in children. It has been withdrawn in some countries but remains in use in many public health programmes. Weight-based dosing; take with a fatty meal.
Also known as: Grisactin, Fulcin
Griseofulvin may reduce the effectiveness of hormonal contraceptives (the pill), increasing the risk of unintended pregnancy.
Unknown mechanism — the INFARMED Prontuário Terapêutico (Annex 7) records possible inhibition of oral contraceptive efficacy.
Ask about intermenstrual bleeding and use of barrier contraception.
Intermenstrual bleeding, missed period.
Recommend an additional barrier contraceptive method during treatment and until one cycle after completion; counsel the patient.
INFARMED Prontuário Terapêutico (11th ed., 2012), Annex 7 — Important Interactions; EMC-UK — Griseofulvin 500 mg Tablets: https://www.medicines.org.uk/emc/product/4385
Griseofulvin may reduce the anticoagulant effect of warfarin, lowering prothrombin time/INR.
Griseofulvin may increase hepatic metabolism (CYP2C9) of coumarin anticoagulants.
Baseline INR and 1–2 weeks after co-administration.
INR falling below the therapeutic range.
Check INR at the start and end of griseofulvin treatment; adjust the warfarin dose if needed.
DailyMed — Gris-PEG (griseofulvin) label, Drug Interactions: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f21314eb-3581-4e06-9fe7-8239cc80ba11
Griseofulvin is very poorly water-soluble — absorption multiplies when taken with a fatty meal; without it the dose may be insufficient.
ALWAYS take with a meal containing fat (site monograph: "fatty meal for reliable absorption").
Prontuário Terapêutico INFARMED, 6.2.2 (griseofulvin — lipid solubility); site monograph (always take with a fatty meal).
Griseofulvin is teratogenic — contraindicated in pregnancy; contraception during and 1 month after treatment (men and women).
Exclude pregnancy before starting; effective contraception until 1 month after completion.
Site monograph (griseofulvin — contraception during and 1 month after); Prontuário 6.2.2.
Griseofulvin is classically contraindicated in porphyria — precipitates acute attacks.
Contraindicated in any type of porphyria.
Prontuário 6.2.2 / EMC-UK griseofulvin SmPC 4.3 (porphyria).
Contraindicated in liver disease — hepatotoxicity and altered metabolism.
Exclude liver disease before prolonged courses.
Site monograph (griseofulvin — liver function in long courses).
Contraindicated in pregnancy: griseofulvin is embryotoxic and teratogenic in animals (anencephaly, hydrocephalus) and interferes with human spermatogenesis. Most sources advise against use during pregnancy, especially in the 1st trimester, except in severe mycosis with no alternative.
Avoid in all trimesters; use only if benefit clearly outweighs risk (severe mycoses — extensive tinea capitis, extensive onychomycosis — with no safe alternative).
Excretion into milk is not well characterised; breastfeeding is advised against during treatment (griseofulvin may cause candidiasis and infant safety is unknown).
Effective contraception mandatory in men and women during and for 1 month after treatment (impairs spermatogenesis and reduces the efficacy of oral contraceptives — use a complementary barrier method).
Prontuário Terapêutico INFARMED — 7.1.2 (Antifungals) and Interactions: "Griseofulvin: possible inhibition of oral contraceptive efficacy" (l. 46053); EMC-UK (MHRA) — Griseofulvin SmPC: https://www.medicines.org.uk/emc/product/2851/smpc (section 4.6: "should not be used in pregnant patients or in those intending to become pregnant").
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Classic oral fungistatic antifungal for hair and skin dermatophytoses in children; today often replaced by terbinafine, but still in use where cost and availability prevail.
Binds fungal tubulin and disrupts mitotic spindle function (metaphase mitosis arrest) — fungistatic: requires drug incorporation into newly formed keratin so the infection grows out with epithelial/nail renewal. Harmless to mammals at therapeutic doses.
Very variable, formulation-dependent absorption (ultramicrosized ≈ 2× microsized); dramatically increased by a fatty meal (the paediatric regimen should include milk/fat); peak 4 h.
Aromatic oxidation (CYP3A4) and demethylation to 6-desmethylgriseofulvin (partially active), conjugated and urinary excreted. POTENT inducer of CYP3A4 and CYP2C9: reduces oral contraceptive and warfarin efficacy (INR falls) — clinically important interactions.
9–21 h; high binding to forming keratin prolongs target-tissue action beyond plasma levels.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
