Supportive therapy is often necessary initially, including fluid therapy and pain relief. Once a diagnosis has been established,
initiate systemic antifungal therapy either empirically or guided by the results of fungal culture. Traditional antifungal
treatments include amphotericin B and itraconazole (Table 1).1
Amphotericin B is a macrolide polyene drug with a broad spectrum of antifungal activity. It appears to be primarily fungistatic
but may be fungicidal against some organisms depending on the drug concentration.25 Marked nephrotoxicosis has been reported in veterinary patients after administration of this agent, although the more expensive
lipid-based formulations appear to be less toxic and have improved tissue penetration. Some controversy exists in the human
literature about the concurrent administration of amphotericin B and azole drugs, since amphotericin B binds to ergosterol
within the fungal cell membrane causing cellular contents to leak, while azole drugs inhibit the synthesis of ergosterol.
Theoretically, therefore, the efficacy of amphotericin may be blunted in patients receiving azole therapy.
Prolonged clinical remission has been reported in dogs given oral itraconazole, and it is probably the most commonly administered
azole drug in dogs with disseminated aspergillosis.23,26 Although fluconazole would be a less expensive option, we are not aware of any reports of successful management of canine
disseminated aspergillosis using this agent. In addition, several studies in the human field suggest poor efficacy of fluconazole
for this condition.27,28
Many new azoles have been developed in recent years, including voriconazole (Vfend—Pfizer). Voriconazole appears to be more
effective against invasive Aspergillus species in people and is associated with fewer adverse events than amphotericin B.29 Other new azoles, including posaconazole and ravuconazole, have been shown to be efficacious against aspergillosis in vitro
but their use in companion animals has not been explored.30
Additional antifungal options include terbinafine and caspofungin. Terbinafine is a squalene epoxidase inhibitor and may work
synergistically with azole drugs.25 It is generally well-tolerated by dogs, and positive results have been reported in dogs with Malassezia species dermatitis.31 Caspofungin is the first member of a new class of antifungal drugs called the echinocandins. It prevents fungal cell wall synthesis by inhibiting a glucan synthase and has been used successfully in people with invasive
aspergillosis who fail to respond to conventional antifungal medications.25 However, we are unaware of any reports of a positive response after the administration of either agent to dogs with disseminated
Survival times for dogs with disseminated aspergillosis are variable, but owners should generally be given a guarded prognosis.
Dogs with mild disease can have prolonged survival after antifungal drug therapy, although many months of treatment are necessary
and relapse may occur if medications are prematurely discontinued. Sadly, more severely compromised dogs often succumb to
complications of their infection or are euthanized because of quality of life concerns.
Whitney Nelson, DVM
Audrey K. Cook, BVM&S, MRCVS, DACVIM, DECVIMCA
Department of Small Animal Clinical Sciences
College of Veterinary Medicine & Biomedical Sciences
Texas A&M University