Differential immunosuppressive action of carbimazole and propylthiouracil.

Carbimazole and Propylthiouracil (PTU) are widely used in the treatment of Graves' disease, although controversy still exists as to whether or not they have any direct effect on the immune system. While many previous studies have investigated the possible effects of one or other of these drugs on the immune system only a few have directly compared the effects of equivalent doses of each drug. This study aimed to examine the effects of both drugs, during the initial 8 weeks of treatment, on various biochemical and immunological parameters. The results obtained showed that while thyroid hormone levels fell at similar rates in both treatment groups, TRAb levels and T cell subset abnormalities returned towards normal more rapidly in patients receiving Carbimazole compared to PTU. These results indicate that the effects of Carbimazole on TRAb levels and T cell subset abnormalities are not due solely to its action in controlling the biochemical features of Graves' disease and provide indirect evidence of an action on the immune system in vivo.