Feline interferon response to 2-amino-5-bromo-6-methyl-4-pyrimidinol (U-25,166).

U-25,166 induced high serum interferon levels in cats at concentrations at least 40 times less than the maximum tolerated dose. Although certain cats responded to U-25,166 by consistently producing higher interferon levels than did other cats, this relationship was not observed if the same animals were injected with Newcastle disease virus or polyriboinosinic:polyribocytidylic acid (poly I:C). Using a biweekly treatment regimen, cats remained responsive to interferon induction by U-25,166 over an 18-week period in which 9 doses of the compound were given. Cats given the compound daily, however, soon became hyporesponsive to interferon induction. Interferon was induced in cats given U-25,166 orally as a suspension or in capsules, but circulating interferon levels were low in cats given the drug by subcutaneous injection.