IMMUNE-MODIFYING DRUGS
Treatment of immune-mediated skin diseases generally requires immunosuppressive drugs, such as corticosteroids. However, some
medications are now available to lessen that need or to replace corticosteroids for long-term management of these conditions.
While generic products for some of these medications are available, their bioavailability is not always equivalent to that
of the parent product. The cost of the branded product is the most common reason why clients wish to use a generic form. It
is recommended to initiate therapy with a branded product and, once full effect has been achieved, then a generic product
may be used if requested by the client. The client must be informed that these generic drugs may not work as well and dosing
may need to be adjusted.
Cyclosporine
Cyclosporine (Atopica—Novartis Animal Health) has both anti-inflammatory and immunosuppressive properties. It targets cell-mediated
immunity, and with its other properties, it results in fewer side effects than corticosteroids. It is used to treat perianal
fistulas and canine atopic dermatitis and can also be an effective maintenance drug for patients with autoimmune diseases
such as pemphigus foliaceus. A double-blinded, randomized study of 29 cats comparing the efficacy of once-daily dosing of
cyclosporine (1 mg/kg) to prednisolone (5 mg/kg) in cats with atopic dermatitis concluded that there was no significant difference
in response.7 Atopica has just been FDA-approved as an oral solution for cats.
Given that this drug is metabolized in the liver, take caution when using it in patients with liver disease. Many other drugs
use the same enzyme system in the liver, and their use can reduce the metabolism of cyclosporine. For example, giving 5 mg/kg/day
ketoconazole orally can help to reduce the cyclosporine dose by up to 50%. By reducing the dose, the risk of side effects
is also reduced. The most common side effects associated with cyclosporine include vomiting, diarrhea, and anorexia.
Cyclosporine is generally given without food, resulting in rapid absorption and the risk of gastrointestinal side effects.
Giving with food, freezing the capsules, splitting the dose (twice daily), or giving with metoclopramide or ketoconazole,
which allows a further reduction in dose, may be effective in reducing the risk of adverse effects. Long-term management requires
finding the lowest effective dose, and patients should have blood work evaluated every three months during the treatment of
active disease and, once stable, at least once a year.
Pentoxifylline
The human product pentoxifylline (Trental—Sanofi-Aventis) is a vasoactive agent with anti-inflammatory properties. It has
been used to treat vasculitis, atopy, and dermatomyositis in dogs. It can take several weeks of treatment with pentoxifylline
to be effective. One study in dogs with familial canine dermatomyositis showed a median response time to treatment of six
weeks.8
This medication should be given with food, and the side effects, while rare, include vomiting, diarrhea, and central nervous
system excitement.
Trilostane
Trilostane (Vetoryl—Dechra Veterinary Products) is indicated for treating Cushing's disease. This synthetic steroid analogue
reduces the synthesis of cortisol, aldosterone, and adrenal androgens. This inhibition is reversible and dose-dependent. Trilostane
significantly reduces the production of progesterone, so it should not be used in breeding animals.
In addition to treating Cushing's disease, trilostane has been used effectively in the treatment of alopecia X. While this
is not considered a severe disease but more of a cosmetic problem, owners may elect to treat it. In one study involving 18
Pomeranians with alopecia X given a high dose of trilostane (11 mg/kg/day), 85% demonstrated improvement of clinical signs
within four to eight weeks, and no adverse effects were reported.9
The clinical dose for the treatment of alopecia X ranges from 2 to 6.7 mg/kg given orally once daily with food. The recommended
initial dose is 2 mg/kg given once or twice daily. Response may take several months, at which time the dose should be tapered
to the lowest effective dose. Side effects are rare and can include diarrhea, vomiting, and lethargy. Patients receiving trilostane
should be monitored with regular ACTH simulation tests.
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