Cinacalcet: new drug. Secondary hyperparathyroidism: where are the clinical data?

(1) Patients who require dialysis for chronic renal failure develop phosphocalcium metabolic disorders that often lead to secondary hyperparathyroidism. Standard treatment consists of a phosphate chelator and vitamin D, along with the use of an appropriate calcium concentration in the dialysis bath, but is difficult to manage. (2) Parathyroid cancer is a rare malignancy frequently associated with hypercalcaemia. (3) Cinacalcet is a calcimimetic agent that reduces the parathormone level. Clinical evaluation includes more than a dozen dose-finding studies and clinical trials. The optimal dose seems to range from 30 to 180 mg/day and varies widely from one patient to another. (4) 3 double-blind placebo-controlled trials, lasting for a maximum of one year and involving a total of 1136 dialysis patients with chronic renal failure, showed no improvement in quality of life with cinacalcet. The target parathormone level was reached by 40% of patients on cinacalcet versus 5% of patients on placebo, while the effects of cinacalcet on calcium levels (-7%) and phosphate levels (-8%) were modest. No impact on bone complications is mentioned in available reports. (5) The assessment of treatment of parathyroid cancer is limited to one ongoing non comparative trial involving 21 patients. (6) During clinical trials, 11% of dialysis patients had low parathormone levels, creating a risk of adynamic bone disease and fractures, but available data are sparse. (7) Two-thirds of patients receiving cinacalcet have episodes of hypocalcaemia, which may in part account for reports of seizures (1.4% of patients), nausea (31%) and vomiting (27%). Many adverse effects seen in animal studies have not been adequately investigated in the clinical setting, such as an increase in the QT interval, thyroid disorders, and sexual dysfunction. Cinacalcet is a powerful CYP 2D6 inhibitor and is also metabolised by isoenzymes CYP 3A4 and CYP 1A2, creating an increased risk of drug interactions. (8) In practice, treatment with cinacalcet seems difficult to manage and to provide only limited benefits. Available assessment reports leave many questions unanswered, and this is a further reason not to use this product outside of clinical trials, either after failure of phosphate chelator and vitamin D therapy (especially as an alternative to surgery) or in parathyroid cancer.