Effects of Oral Cimetidine on Parathyroid Hormone and Calcitonin Plasma Levels in Uremic Patients

Reports concerning the effects of Cimetidine on parathyroid hormone levels in primary hyperparathyroidism (1–4) and in secondary hyperparathyroidism of renal failure (5–8) are increasing in number, but lead to disagreeing conclusions. These discrepancies are unclear and could be possibly explained by: 1) a variable compliance to treatment, since no measurement of plasma levels of Cimetidine has been made in these reports, 2) differences in specificity of parathyroid hormone immunoassays, since, in a studied group of hemodialysed patients, the lowering effect of Cimetidine on parathyroid hormone levels previously observed using a carboxyterminal antiserum (5), was not confirmed when the same samples were assayed a second time using an aminoterminal antiserum (9). It has also been suggested (8) that Cimetidine could act on the metabolic fate of circulating parathyroid hormone rather than on its secretion, thus explaining differences between results derived from either carboxy or aminoterminal immunoassays.