A 33-year-old man presents to the physician for a follow-up visit. Past medical history includes gastroesophageal reflux, peptic ulcer disease, and renal calculi. He says he has been doing well apart from some back and joint pain. Physical examination is notable for mild midline vertebral tenderness, but no joint swelling, redness, or significant pain is appreciated. Laboratory studies reveal an elevated serum calcium level. Further evaluation reveals primary hyperparathyroidism. He is referred for parathyroidectomy but declines surgery and is subsequently started on cinacalcet.
E) Sensitizes calcium-sensing receptors
This patient's clinical features and past medical history are concerning for hyperparathyroidism, which is confirmed in the vignette. The elevated parathyroid hormone (PTH) levels cause hypercalcemia via multiple pathways. Cinacalcet sensitizes calcium-sensing receptors in the parathyroid gland and reduces PTH secretion.
Answer choice A: Inhibits calcitriol production, is incorrect. Steroids inhibit the production of calcitriol (found in activated macrophages), the active form of vitamin D that allows calcium absorption in the gastrointestinal tract.
Answer choice B: Inhibits osteoclast activation, is incorrect. Osteoclast activation is inhibited by denosumab which binds to and inhibits RANKL, a type II transmembrane protein.
Answer choice C: Inhibits osteoclast function, is incorrect. Bisphosphonates are pyrophosphate analogs that are uptaken by already-activated osteoclasts. Bisphosphonates disrupt proper degradation of osseous tissue by osteoclasts.
Answer choice D: Promotes calcium loss in the urine, is incorrect. Loop diuretics inhibit the Na-K-Cl cotransporter (NKCC) in the thick ascending limb of the Loop of Henle. This ultimately reduces the net positive charge in the tubular lumen preventing calcium ions from being reabsorbed.
Key Learning Point
Cinacalcet sensitizes calcium-sensing receptors on parathyroid gland cells. This prevents excessive parathyroid hormone (PTH) secretion by the parathyroid glands. This helps reduce the hypercalcemia seen in hyperparathyroidism.
