indication

For the treatment of secondary hyperparathyroidism in patients with Chronic Kidney Disease who are on hemodialysis or peritoneal dialysis. Also for the treatment of hypercalcemia in patients with parathyroid carcinoma.

pharmacology

Cinacalcet is a drug that acts as a calcimimetic (i.e. it mimics the action of calcium on tissues). Secondary hyperparathyroidism (HPT) in patients with chronic kidney disease (CKD) is a progressive disease, associated with increases in parathyroid hormone (PTH) levels and derangements in calcium and phosphorus metabolism. Increased PTH stimulates osteoclastic activity resulting in cortical bone resorption and marrow fibrosis. The goals of treatment of secondary hyperparathyroidism are to lower levels of PTH, calcium, and phosphorus in the blood, in order to prevent progressive bone disease and the systemic consequences of disordered mineral metabolism. In CKD patients on dialysis with uncontrolled secondary HPT, reductions in PTH are associated with a favorable impact on bone-specific alkaline phosphatase (BALP), bone turnover and bone fibrosis. Cinacalcet reduces calcium levels by increasing the sensitivity of the calcium sensing receptor to extracellular calcium.

mechanism of action

The calcium-sensing receptors on the surface of the chief cell of the parathyroid gland is the principal regulator of parathyroid hormone secretion (PTH). Cinacalcet directly lowers parathyroid hormone levels by increasing the sensitivity of the calcium sensing receptors to activation by extracellular calcium, resulting in the inhibition of PTH secretion. The reduction in PTH is associated with a concomitant decrease in serum calcium levels.

toxicity

Doses titrated up to 300 mg once daily have been safely administered to patients on dialysis. Overdosage of cinacalcet may lead to hypocalcemia.

biotransformation

Metabolism is hepatic by multiple enzymes, primarily CYP3A4, CYP2D6, and CYP1A2. After administration of a 75 mg radiolabeled dose to healthy volunteers, cinacalcet was rapidly and extensively metabolized via: 1) oxidative N-dealkylation to hydrocinnamic acid and hydroxy-hydrocinnamic acid, which are further metabolized via ß-oxidation and glycine conjugation; the oxidative N-dealkylation process also generates metabolites that contain the naphthalene ring; and 2) oxidation of the naphthalene ring on the parent drug to form dihydrodiols, which are further conjugated with glucuronic acid.

absorption

Rapidly absorbed following oral administration.

half life

Terminal half-life is 30 to 40 hours. The mean half-life of cinacalcet is prolonged by 33% and 70% in patients with moderate and severe hepatic impairment, respectively.

route of elimination

Cinacalcet is metabolized by multiple enzymes, primarily CYP3A4, CYP2D6 and CYP1A2. Renal excretion of metabolites was the primary route of elimination of radioactivity.

drug interactions

Erythromycin: The macrolide, erythromycin, may increase the serum concentration and toxicity of cinacalcet.

Itraconazole: Itraconazole may increase the effect and toxicity of cinacalcet.

Ketoconazole: Ketoconazole may increase the effect and toxicity of cinacalcet.

Tamoxifen: Cinacalcet may decrease the therapeutic effect of Tamoxifen by decreasing the production of active metabolites. Concomitant therapy should be avoided.

Tamsulosin: Cinacalcet, a CYP2D6 inhibitor, may decrease the metabolism and clearance of Tamsulosin, a CYP2D6 substrate. Monitor for changes in therapeutic/adverse effects of Tamsulosin if Cinacalcet is initiated, discontinued, or dose changed.

Telithromycin: Telithromycin may reduce clearance of Cinacalcet. Consider alternate therapy or monitor for changes in the therapeutic/adverse effects of Cinacalcet if Telithromycin is initiated, discontinued or dose changed.

Tolterodine: Cinacalcet may decrease the metabolism and clearance of Tolterodine. Monitor for adverse/toxic effects of Tolterodine.

Tramadol: Cinacalcet may decrease the effect of Tramadol by decreasing active metabolite production.

Trimipramine: The strong CYP2D6 inhibitor, Cinacalcet, may decrease the metabolism and clearance of Trimipramine, a CYP2D6 substrate. Consider alternate therapy or monitor for changes in therapeutic and adverse effects of Trimipramine if Cinacalcet is initiated, discontinued or dose changed.

Venlafaxine: Cinacalcet, a CYP2D6 inhibitor, may decrease the metabolism and clearance of Venlafaxine, a CYP2D6 substrate. Monitor for changes in therapeutic/adverse effects of Venlafaxine if Cinacalcet is initiated, discontinued, or dose changed.

Voriconazole: Voriconazole, a strong CYP3A4 inhibitor, may increase the serum concentration of cinacalcet by decreasing its metabolism. Monitor for changes in the therapeutic and adverse effects of cinacalcet if voriconazole is initiated, discontinued or dose changed.

Zuclopenthixol: Cinacalcet, a strong CYP2D6 inhibitor, may increase the serum concentration of zuclopenthixol by decreasing its metabolism. Consider alternate therapy or monitor for changes in the therapeutic and adverse effects of zuclopenthixol if cinacalcet is initiated, discontinued or dose changed.