Griseofulvin

This information on drug interactions with antimicrobials is intended for use as a guide and not as a complete reference source

Antimicrobial	Interacting Drug	Comment
Griseofulvin (antifungal)	Drugs metabolised by cytochrome P450	Griseofulvin is a hepatic microsomal enzyme inducer. It may reduce efficacy of concomitantly administered medicinal products that are metabolised by cytochrome P450 34A (e.g. Methadone).
	Oral contraceptives	Efficacy of oral contraception is reduced during griseofulvin therapy and for four weeks post therapy cessation. In view of the contraindication in pregnancy and of the possible sequelae of male patients fathering a child during therapy, all sexually active patients should use additional barrier contraception, such as condoms, throughout griseofulvin therapy, and for four weeks (female) and 6 months (male) post therapy cessation.
	Etonogestrel (subdermal) and Nuvaring^®	Griseofulvin might reduce the contraceptive reliability of the etonogestrel implant. There is a risk of teratogenic effects with griseofulvin. Recommend alternative methods (IUDs, depot, or barrier methods) should be used during treatment with, and for four weeks after griseofulvin is stopped. Griseofulvin may reduce effectiveness of Nuvaring® – consult product spc.
	Ulipristal	The efficacy of Ulipristal is predicted to be reduced by griseofulvin. Avoid concurrent use, and for 4 weeks after stopping griseofulvin. For emergency contraception, recommend alternative methods.
	Levonorgestrel	During and within 28 days of stopping griseofulvin, a copper intra-uterine device is the first-line option for emergency contraception. In women who decline or who are not eligible for a copper IUD, 3 mg of levonorgestrel should be given as a single dose.
	Warfarin	The anticoagulant effects of warfarin can be reduced by griseofulvin. Monitor INR regularly for the duration of therapy and for 8 days post therapy cessation.
	Alcohol	Reports of Disulfiram type reaction. Avoid alcohol and all alcohol containing products while undergoing therapy. Monitor for flushing, tachycardia.
	Enzyme inducers	Concurrent administration of other medicinal products that induce metabolising enzymes may result in a reduction of griseofulvin efficacy e.g primidone, phenobarbital.
	Ciclosporin	Griseofulvin may reduce serum levels of ciclosporin.