Evaluating Alternative Medical Therapies in Primary Hyperparathyroidism

To conduct a double-blinded, placebo-controlled, randomized intervention study to investigate whether mineralocorticoid receptor (MR) antagonism, alone or in combination with cinacalcet, is an effective therapy for primary hyperparathyroidism (P-HPTH).

Hypothesis: MR antagonism, as a monotherapy or in combination with a calcimimetic, is a mechanism to lower parathyroid hormone (PTH) in primary hyperparathyroidism (P-HPTH).

Study Design: Sixty subjects with P-HPTH will be enrolled to randomly receive eplerenone (a potassium-sparing diuretic that directly blocks the MR), amiloride (a potassium-sparing diuretic that does not directly block the MR), or placebo for 4 weeks. Thereafter, all subjects will receive cinacalcet therapy (a calcimimetic that lowers PTH) in addition to their randomized intervention for an additional 2 weeks.

Anticipated Results: In this proof-of-concept study, eplerenone therapy will lower PTH, serum calcium, and markers of bone resorption in P-HPTH, when compared to placebo. The PTH response to amiloride will resemble that of placebo, suggesting that the eplerenone mediated reductions in PTH are specific to interactions with the MR. Combination therapy with eplerenone + cinacalcet will result in additive or synergistic reductions in PTH, when compared to placebo + cinacalcet or placebo + amiloride.

Implications: MR antagonism (alone or in combination with cinacalcet) may be a mechanism to lower PTH and calcium in P-HPTH, thereby identifying a new potential option in the limited medical therapies for P-HPTH.