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Griseofulvin (Fulvicin)
Revised: October 25, 2021
Published: January 01, 2001

(For veterinary information only)

The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you use drugs on your pet without your veterinarian's advice. 

It is our policy not to give dosing information over the internet.

Brand Name: Fulvicin

Available in 125 mg and 250 mg ultramicrosize formula tablets


This medication is used to treat ringworm, a fungal infection of the skin involving fungi called dermatophytes. While it is possible for a ringworm lesion to be localized and require only topical therapy, this is not the usual situation; oral medication is generally necessary to control the skin disease. This medication should be continued until the patient has been cultured negative. If it is discontinued prematurely (if the skin disease simply appears to have resolved but has not been re-cultured and confirmed resolved), the skin disease may recur.

Griseofulvin is produced by Penicillium bacteria. It is extracted and made into small particles that are either microsized (approximately 4 microns in diameter) or ultramicrosized (less than 1 micron in diameter). Dosing is different depending on which form of griseofulvin you are using. Ultramicrosized griseofulvin has much better absorption into the body from the intestinal tract compared to microsized griseofulvin.

Griseofulvin has no other uses beyond treating ringworm and, in this day and age, griseofulvin is rapidly being supplanted by terbinafine and and itraconazole, which have less side effects potential. Still, griseofulvin has been the classical treatment of ringworm for decades and is still effective and is still being prescribed.

See more detailed information on ringworm and its management.

How this Medication Works

Griseofulvin acts by interfering with the microtubular structure of cell division so that fungal cells cannot reproduce. This enables the host's immune system to gain the upper hand and eliminate the infection. Griseofulvin is effective only against ringworm fungi; other fungi are not affected.

Side Effects

The most common side effect associated with this medication is nausea. Vomiting or diarrhea would indicate that the medication is upsetting the patient's stomach and alternative treatment should be considered. If this is not possible, anti-nausea medications may help. Kittens are more prone to side effects than adult cats.

Griseofulvin may not be given to cats infected with the feline immunodefiency virus as these individuals commonly develop blood dyscrasias (imbalances). More specifically, their white blood cell counts drop so low that their immune system is compromised. This side effect can occur in non-FIV+ cats as well, but is quite rare. Some specialists recommend monitoring white blood counts every two weeks while a feline patient is on griseofulvin just to make sure this serious side effect is not occurring. Persian cats seem more prone to this side effect than other breeds but not as prone as FIV+ cats.

Interactions with Other Drugs

Concurrent use of phenobarbital (medication for seizures) will reduce absorption of griseofulvin from the patient's GI tract.

The following drugs have decreased blood levels and may not work as well when combined with griseofulvin: theophylline (an oral airway dilator), cyclosporine (an immunomodulator), and aspirin (a blood thinner/anti-inflammatory).

Concerns and Cautions

Griseofulvin works best if given with a fatty meal (the oil from oil-packed tuna cans or butter should work well).

Griseofulvin can be harmful to the liver and should be avoided in patients who have known liver disease.

Griseofulvin causes birth defects if given to pregnant animals.

If you miss a dose, do not double up on the next dose. Simply give the medication when it is remembered or pick up with the next dose, allowing at least the proper interval between doses according to the given instructions.

Never give this medication to a pregnant pet.

Pregnant women should wear gloves when handling this medication.

Recurrence of ringworm infection is not uncommon if an incomplete course of medication is given. Griseofulvin should be given until a fungal culture is negative.

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