Effect of immunosuppressive drug therapy on blood urea nitrogen concentration in dogs with azotemia.

Azotemic dogs receiving prednisone and azathioprine to enhance renal allograft survival had higher blood urea nitrogen (BUN):serum creatinine (SC) ratios, when compared with nontreated dogs with induced azotemia. The difference in ratios probably was attributable to increased BUN content secondary to the catabolic effects of the drugs used. However, dogs with naturally occurring renal failure had BUN:SC ratios that were similar to those for dogs receiving the catabolic drugs. It was concluded that even though catabolic drugs may influence BUN:SC ratios, the multiplicity of other factors affecting BUN and SC may interact to cause a wide range of BUN:SC ratios under conditions of naturally occurring primary renal failure in the dog.