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Terbinafine (Lamisil)
Revised: February 21, 2023
Published: May 09, 2005

(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: Lamisil

Available in 250 mg tablets; 1% gel for topical use; film-coated oral granules    


Treating infection centers on exploiting a biological difference between the infectious agent and its host so that the infectious agent can be killed and the host will be unaffected. In the case of a fungal infection, the cell wall of the fungus is the usual focus of anti-fungal medication. Happily, fungal cells (as well as bacterial and plant cells) employ a fibrous cell wall to encase their inner structures while animal cells use a cell membrane, which is a completely different structure. The fungal cell wall forms a thick armor and contains a specific form of vitamin D known as ergosterol, without which many fungi cannot live. Terbinafine inhibits the production of ergosterol in such a way as to lead to the build-up of the ergosterol precursor known as squalene. Having the wrong structural components disrupts the function of the cell wall as a barrier. Without the protection of its outer armor (the cell wall), the fungal cell will die. None of this affects the animal cell because animal cells, as mentioned, do not even have cell walls.

How This Medication is Used

After terbinafine is taken orally, it concentrates in the skin and fat tissues of the body. The high levels in the skin make terbinafine an ideal treatment for fungal infection of the skin. For veterinary patients, this typically would relate to ringworm infection (dermatophytosis). Terbinafine has activity against other types of fungi (in particular, Aspergillus species) but at this time it is mostly used against ringworm. Terbinafine is dosed 1-3 times daily depending on what fungus is being treated.

Terbinafine is best given with food. If a dose is accidentally skipped, do not double up on the next dose. Simply give the dose when it is remembered and time the next dose accordingly.

Keep away from light and store at room temperature.

Side Effects

The most common side effect is an upset stomach.

Serious side effects have not been reported in companion animals, but in humans, there have been cases of liver failure, skin reactions, and bone marrow suppression. The manufacturer of terbinafine recommends that it not be used in patients with active liver disease or with poor kidney function.

Because terbinafine uses a different mechanism of ergosterol inhibition, it does not have the hormonal side effects that the "azole" group of antifungals (ketaconazole, itraconazole) has.

Interactions with Other Drugs

Many other drugs are removed from the body via the same inactivation pathway as terbinafine: selegiline (an MAO inhibitor), amitraz (a common tick-killing product), beta-blockers (heart medicines), tricyclic antidepressants (like clomipramine and amitriptyline), narcotic pain relievers, and selective serotonin reuptake inhibitors (like fluoxetine). This means that these medications may last longer or act with more strength than expected.

Terbinafine may facilitate the removal of cyclosporine (an immune modulator used in the treatment of immune-mediated diseases as well as allergies) from the body. This means that cyclosporine will not be as effective when taken with terbinafine.

Concurrent use of the antacid cimetidine will slow the removal of terbinafine from the body (thus increasing its levels). 

Concerns and Cautions

  • Terbinafine should be stored at room temperature and protected from light exposure.
  • Terbinafine should not be used in patients with kidney or liver disease.
  • Terbinafine should not be used in pregnancy or lactation.
  • If you accidentally skip a dose, do not double up on the next dose. Simply pick up normally with the next dose.

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

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