Propylthiouracil-induced immune-mediated disease in the cat

An immune-mediated disease was produced in 9 of 17 (53%) normal healthy cats by daily p.o. administration of 150 mg of 6-propylthiouracil (PTU). This disease syndrome is characterized by lethargy, weight loss, lymphadenopathy, hemolytic anemia, a positive direct antiglobulin test (DAT) and antinuclear antibodies (ANA). The duration of drug administration before the development of a positive DAT and/or ANA ranged from 3 to 8 weeks (Mean +/- S.E.M. = 4.5 +/- 0.6), whereas the duration before the onset of clinical signs ranged from 4 to 8 weeks (6.1 +/- 0.6 weeks). On cessation of PTU administration, clinical signs resolved in all cats within 2 weeks, and the DAT and test for ANA were negative within 1 to 4 weeks (1.9 +/- 0.4 weeks). During nine PTU-rechallenge periods in four cats, both the mean time to develop a positive DAT and ANA (2.5 +/- 0.8 weeks) and the mean time to develop overt clinical signs (2.6 +/- 0.7 weeks) were shorter than similar mean times in the initial PTU treatment period (P less than .01). During nine episodes of PTU-induced disease in seven cats, PTU administration was discontinued and replaced with 150 mg of 6-propyluracil (PU), a nonsulfur analog of PTU. Resolution of both clinical and serologic signs of disease occurred in seven of the nine disease episodes within 1 to 3 weeks (2.1 +/- 0.4 weeks). In the two cats whose disease did not resolve on PU, one was sacrificed after 1 week of PU administration, without clinical or serologic resolution, because of the severity of the PTU-induced disease.(ABSTRACT TRUNCATED AT 250 WORDS)