Terbinafine for Fungal Infections in Dogs

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Terbinafine (Lamisil) is an antifungal medication. Vets may prescribe it as an oral tablet or a topical ointment. Here's how both forms are used in dogs, with concerns to watch for.

Terbinafine for dogs at a glance

What is terbinafine, and how does it work?

Terbinafine is a medication veterinarians may use to treat fungal infections in dogs. These infections occur most often on the skin. Terbinafine works by preventing the creation of ergosterol, a main component of affected fungal cell membranes.

Terbinafine can kill the fungal organisms causing ringworm or dermatophytosis (Microsporum, Trichophyton). This is also called fungicidal activity. For most other fungal organisms, terbinafine blocks fungal growth.

What is terbinafine used for in dogs?

Terbinafine works best against the fungal organisms that cause ringworm (dermatophytosis). This includes Microsporum and Trichophyton.

Terbinafine may also be used for other fungal infections, including:

• Candida

• Aspergillus

• Blastomyces

• Coccidioidomycosis

• Histoplasma

• Sporothrix

• Cryptococcus

• Malassezia

Terbinafine is not FDA approved for use in dogs. Use by a veterinarian is considered "off-label." Off-label use of medications is common in veterinary medicine.

There are other antifungals in the azole class (itraconazole, fluconazole, and ketoconazole) that may be preferred over terbinafine for treating some infections. But terbinafine interacts with far fewer medications and carries a lower risk of side effects. This may make it a preferred treatment option in some dogs.

How is terbinafine given to dogs?

Terbinafine is available as a tablet or a topical ointment you apply directly on your dog's skin. The dose can vary depending on the type of fungal organism being treated and where the infection is located. It is important to consult with your veterinarian for the most appropriate dose for your dog.

Oral tablets

Oral terbinafine tablets come in a 250 mg dose. The most common brand name is Lamisil, but there are many generic forms.

You may give your dog terbinafine pills with or without food. It has less pronounced side effects compared with the azole antifungals. If you notice vomiting after your dog receives a dose, giving the medication with food may help.

Topical cream

Terbinafine also comes over the counter as a 1% cream or ointment. Veterinarians may recommend this option if the disease is not widespread. This is especially true for single Malassezia or ringworm lesions.

The topical 1% terbinafine ointment can usually be applied to a single lesion once a day. Some evidence suggests that every-other-day frequency may be appropriate for ringworm. Treatment for ringworm may take weeks or even months. It is important to follow up with your veterinarian before discontinuing ringworm treatment.

The length of time for treating fungal infections can vary. Some Malassezia skin infections need only 2 to 4 weeks of treatment. But many fungal infections may take weeks or months. In rare cases, a dog may need to take an antifungal medication for a year or longer.

What are the common side effects of terbinafine in dogs?

The most common side effects dogs may have while taking terbinafine are gastrointestinal upset:

• Vomiting

• Reduced appetite

• Diarrhea

The terbinafine tablet has an unpleasant taste to dogs. This may lead to signs of nausea or avoidance when trying to give the medication.

Signs of excessive panting have also been reported in dogs taking terbinafine, though the cause is unclear.

What are the most serious risks of terbinafine for dogs?

Be careful using terbinafine in dogs with impaired kidney function or liver function. Serious worsening of disease can occur.

In humans, loss of taste and smell has been reported with terbinafine. But this effect cannot be well-assessed in animals. Be cautious using terbinafine in dogs that need a sense of smell for high function, including working or hunting dogs.

Use caution if giving terbinafine to pregnant, lactating, or breeding dogs. There is little information available on use. But studies in rats have not shown the same toxic effects as azole antifungals have. In humans, health professionals discourage use for nursing mothers. This is because terbinafine can enter milk.

Does terbinafine interact with any other dog medications?

Terbinafine interacts with far fewer medications compared with azole antifungals. But there are still a few interactions to know about. This does not mean you cannot give your dog these medications together. But discuss with your veterinarian the benefits and risks of giving your dog terbinafine along with the following medications:

• Cimetidine

• Cyclosporine

• Fluconazole

• Rifampin

Terbinafine does inhibit the CYP2D6 gene in people. Because of this, terbinafine may interact with the following medications in dogs:

• Antiarrhythmics (lidocaine, mexiletine, procainamide)

• Beta blockers (propranolol, atenolol)

• Codeine

• Dextromethorphan

• Doxorubicin

• Monoamine oxidase inhibitors (selegiline)

• Methadone

• Metoclopramide

• Ondansetron

• Selective serotonin receptor inhibitors (fluoxetine)

• Tamsulosin

• Tramadol

• Trazodone

• Tricyclic antidepressants (amitriptyline, clomipramine)

What should you do if your dog misses a dose of terbinafine?

Terbinafine may be given to your dog once or twice a day. Follow your veterinarian's instructions. Try to give your dog any missed dose as close as possible to when it was due or when the next dose is due.

Then consider these guidelines, depending on your dog's situation:

• If your dog takes the medication once every 24 hours, and less than 12 hours have passed since the missed dose, consider giving a dose as soon as possible. Then start giving future doses 24 hours apart from the new dose time.

• If your dog takes terbinafine once every 24 hours, and it's been more than 12 hours since you gave your dog their dose, skip the missed dose, and wait until the next dose of the medication is due.

• If your dog takes the medication every 12 hours and more than 6 to 8 hours have passed since the missed dose, skip the missed dose. Then give your dog their next dose when it's due.

If you have specific questions about doses or missed doses, contact your veterinarian.

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