IMMUNOSUPPRESSIVE DRUG THERAPY
Immunosuppressive drugs can be used effectively in cats with chronic diarrhea due to IBD, especially when dietary therapy
has not improved or completely resolved clinical signs. Immunosuppressive drug therapy is also indicated in the treatment
of intestinal lymphoma along with adjunctive therapy.
IBD, the persistent inflammation of the GI tract without any identifiable pathogen or trigger, is one of the most common causes
of chronic diarrhea in cats. Corticosteroids remain the cornerstone of treatment in cats with histologic evidence of otherwise
unexplained intestinal inflammation (usually lymphoplasmacytic or eosinophilic). Prednisolone is preferred to prednisone because
of increased bioavailability in cats.
The starting dose for mild to moderate cases is 1 to 2 mg/kg/day; in more severe cases, this dose may be increased to 4 mg/kg/day
(Table 3). It is generally preferable to divide the daily dose into two equal portions. Once the clinical signs are controlled, the
dosage can be tapered by 25% every three to four weeks.17 Cats with mild disease can often be controlled with a modest dose (0.5 mg/kg) given every other day. If the corticosteroid
dose is reduced too rapidly, clinical signs may recur. The goal is to maintain the patient on the lowest effective dose. Some
cats may eventually no longer need the prednisolone, but others may require long-term therapy.
If prednisolone is poorly tolerated, budesonide can be used as an alternative. This locally acting corticosteroid undergoes
extensive first-pass metabolism in the liver, so systemic exposure is theoretically minimized. Budesonide has not been thoroughly
evaluated in cats, but it produces fewer unwanted side effects in dogs when compared with prednisone.18 However, long-term use is still associated with suppression of the pituitary-adrenal axis, indicating some generalized effects.
The recommended dose is 1 mg/cat orally every 24 hours (Table 3). Budesonide is expensive and must be compounded before it can be used in cats.
In some patients with refractory IBD or intestinal small cell lymphoma, chlorambucil should be considered.19 This alkylating, antineoplastic, and immunosuppressive agent may be used in conjunction with prednisolone in these cases.
Various dose schedules have been described; we usually recommend 2 mg/cat orally every 48 hours (Table 3). It may cause vomiting or a decrease in appetite in some individuals, and the dose or frequency of administration may need
to be modified if these adverse effects occur. The most serious side effect of chlorambucil is myelosuppression, so it is
important to perform a complete blood count every month or two.