Altered metabolism and decreased efficacy of prednisolone and prednisone in patients with hyperthyroidism

To evaluate the effect of hyperthyroidism on the protein binding and metabolism of prednisolone, eight subjects with hyperthyroidism were investigated before and after thyroid status returned to normal. Hyperthyroidism was associated with a reduced volume of distribution of prednisolone, a decreased systemic availability of prednisolone after oral prednisone, a displacement of the prednisolone ⇄ prednisone equilibrium toward prednisone, and an increased nonrenal clearance of unbound prednisolone in the presence of an impaired 6β‐hydroxyprednisolone formation. After oral prednisone or intravenous prednisolone, patients with hyperthyroidism had lower albumin‐bound, transcortin‐bound, and unbound concentrations of prednisolone but normal affinities of albumin and transcortin for prednisolone binding. These differences in prednisolone plasma concentrations were biologically relevant, because the capacity of these plasma samples to inhibit allogeneically stimulated lymphocytes was lower by 70% in the hyperthyroid than in the euthyroid state. Thus hyperthyroidism reduces the biologic effect of prednisolone and exhibits a differential effect on various enzymes involved in the catabolism of prednisolone. Clinical Pharmacology and Therapeutics (1988) 44, 510–521; doi: 10.1038/clpt.1988.188