A review of selected systemic antifungal drugs for use in dogs and cats - Veterinary Medicine
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A review of selected systemic antifungal drugs for use in dogs and cats
This pharmacologist reviews a few of your antifungal choices, specifically the azoles andterbinafine. These drugs have a broad spectrum of activity—with some important differences.


VETERINARY MEDICINE


Pharmacokinetics

Similar to itraconazole, the oral absorption of posaconazole is increased when it is administered with food and decreased when it is administered with gastric acid suppression therapy. In dogs that received 10 mg/kg, the half-life was seven hours, the oral bioavailability was 27% in fed dogs, the CMAX was 3.5 μg/ml, and the TMAX was three hours.34,35 Posaconazole is primarily metabolized and inactivated by glucuronide conjugate formation in most species. No pharmacokinetic or metabolism studies are available in cats.

Drug interactions and adverse effects

Posaconazole should be used cautiously in cats; dose extrapolation may not be appropriate because of decreased formation of glucuronide conjugates in cats. However, a single case report of posaconazole (5 mg/kg orally once a day for 16 weeks) administered to a cat with an itraconazole-resistant Aspergillus species infection demonstrated efficacy with minimal adverse effects, which included erythema and pruritus of the pinna and superficial excoriations of the temporal region.36

Posaconazole's adverse effect profile and drug-drug interactions are expected to be similar to those of itraconazole.34 Gastrointestinal adverse effects such as nausea, vomiting, and diarrhea are commonly reported in people. Complete blood counts and serum chemistry profiles should be evaluated routinely during long-term therapy as with the other antifungals. In dogs, posaconazole at doses as low as 3 mg/kg/day caused neuronal phospholipidosis in the peripheral nervous system.34 Higher doses also affected the CNS, although no neurologic deficiencies were observed with either dose. In people receiving posaconazole, cardiovascular effects including hypertension and hypotension have also been reported.34

TERBINAFINE

Terbinafine is not an azole antifungal but is classified as an allylamine. It is available as 250-mg tablets. Clinical reports of terbinafine use in dogs and cats are sparse and limited primarily to Malassezia species and dermatophyte infections.37,38 The typical cost of terbinafine to treat a 44-lb dog (30 mg/kg orally once a day) is about $1/day.

Potential indications

Terbinafine has a broad spectrum of activity against yeast and fungi, including dermatophytes.39 Terbinafine is typically active against Aspergillus species, Blastomyces dermatitidis, Cryptococcus neoformans, Histoplasma capsulatum, Microsporum canis, Malassezia pachydermatis, and Sporothrix schenckii; however, in vivo efficacy studies are lacking.40 Candida species may be less sensitive to terbinafine, so other antifungals may be a better choice.40

Pharmacokinetics

Minimal pharmacokinetic data are available for terbinafine use in dogs or cats. The oral bioavailability in dogs is approximately 46%.41 In dogs, terbinafine is primarily eliminated by hepatic metabolism with the metabolites eliminated in the urine. In people, terbinafine exhibits high plasma protein binding (> 99%).41

Terbinafine administered in cats at 10 to 20 mg/kg orally once a day resulted in median plasma concentrations of 1.38 μg/ml after nine days, increasing to 2.19 and 4.13 μg/ml 60 and 120 days after administration, respectively.37 Cats given terbinafine at 30 to 40 mg/kg once a day had median plasma concentrations of 1.69, 1.89, and 5.48 μg/ml at days 9, 60, and 90, respectively.37 Clinical trials in cats infected experimentally with Microsporum canis have indicated 30 to 40 mg/kg orally once daily was effective in clearing the infections.37

Adverse effects

Terbinafine is typically well-tolerated, but adverse effects can occur. Nausea and vomiting have been reported in cats treated with terbinafine, but these effects decreased when the drug was administered with food.38 Rare but serious adverse effects such as hepatotoxicosis, neutropenia, and toxic epidermal necrolysis have been reported in people.16


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Source: VETERINARY MEDICINE,
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