Mechanism of Action

Secondary HPT in patients with CKD is a progressive disease, associated with increases in 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 HPT are to lower the levels of PTH, calcium, and phosphorus in the blood in order to prevent progressive bone disease and the systemic consequences of disordered mineral metabolism. Reductions in PTH are associated with a decrease in bone turnover and bone fibrosis in patients with CKD on dialysis and uncontrolled secondary HPT.

The calcium-sensing receptor on the surface of the chief cell of the parathyroid gland is the principal regulator of PTH synthesis and secretion. Sensipar (cinacalcet) directly lowers PTH levels by increasing the sensitivity of the calcium-sensing receptor to extracellular calcium. The reduction in PTH is associated with a concomitant decrease in serum calcium levels. Measurements of PTH during the Sensipar (cinacalcet) studies were obtained using the Nichols iPTH immunoradiometric assay.

Pharmacodynamics

Reduction in iPTH levels correlated with the plasma cinacalcet concentrations in patients with CKD. The nadir in iPTH level occurs approximately 2 to 6 hours postdose, corresponding with the maximum plasma concentration (Cmax) of cinacalcet. After steady-state cinacalcet concentrations are reached (which occurs within 7 days of dose change), serum calcium concentrations remain constant over the dosing interval in patients with CKD.

Pharmacokinetics

Absorption and Distribution

After oral administration of cinacalcet, Cmax is achieved in approximately 2 to 6 hours. Cinacalcet Cmax and AUC(0-inf) were increased by 82% and 68%, respectively, following administration with a high-fat meal compared with fasting in healthy volunteers. The Cmax and AUC(0-inf) of cinacalcet were increased by 65% and 50%, respectively, when cinacalcet was administered with a low-fat meal compared with fasting.

After absorption, cinacalcet concentrations decline in a biphasic fashion with a terminal half-life of 30 to 40 hours. Steady-state drug levels are achieved within 7 days, and the mean accumulation ratio is approximately 2 with once-daily oral administration. The median accumulation ratio is approximately 2 to 5 with twice-daily oral administration. The AUC and Cmax of cinacalcet increase proportionally over the dose range of 30 to 180 mg once daily. The pharmacokinetic profile of cinacalcet does not change over time with once-daily dosing of 30 to 180 mg. The volume of distribution is approximately 1000 L, indicating extensive distribution. Cinacalcet is approximately 93% to 97% bound to plasma protein(s). The ratio of blood cinacalcet concentration to plasma cinacalcet concentration is 0.80 at a blood cinacalcet concentration of 10 ng/mL.

Metabolism and Excretion

Cinacalcet is metabolized by multiple enzymes, primarily CYP3A4, CYP2D6, and CYP1A2. After administration of a 75 mg radiolabeled dose to healthy volunteers, cinacalcet was metabolized via: 1) oxidative N-dealkylation to hydrocinnamic acid and hydroxy-hydrocinnamic acid, which are further metabolized via βoxidation 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 forming dihydrodiols, which are further conjugated with glucuronic acid. The plasma concentrations of the major circulating metabolites, including the cinnamic acid derivatives and glucuronidated dihydrodiols, markedly exceed the parent drug concentrations. The hydrocinnamic acid metabolite and glucuronide conjugates have minimal or no calcimimetic activity. Renal excretion of metabolites was the primary route of elimination of radioactivity. Approximately 80% of the dose was recovered in the urine and 15% in the feces.

Drug Interactions

In vitro studies indicate that cinacalcet is a strong inhibitor of CYP2D6, but not an inhibitor of CYP1A2, CYP2C9, CYP2C19, and CYP3A4. In vitro induction studies indicate that cinacalcet is not an inducer of CYP450 enzymes. Tables 3 and 4 list the findings from in vivo drug-drug interaction studies.

Table 3: Effect of co-administered drugs on cinacalcet

Table 4: Effect of cinacalcet co-administration on other drugs

Hepatic Impairment

The disposition of a 50 mg Sensipar (cinacalcet) single dose was compared between patients with hepatic impairment and patients with normal hepatic function. Cinacalcet exposure(AUC(0-inf)) was comparable between healthy volunteers and patients with mild hepatic impairment. However, in patients with moderate and severe hepatic impairment (as indicated by the Child-Pugh method), cinacalcet exposures (AUC(0-inf)) were 2.4 and 4.2 fold higher, respectively, than that in healthy volunteers. The mean half-life of cinacalcet increased from 49 hours in healthy volunteers to 65 hours and 84 hours in patients with moderate and severe hepatic impairment, respectively. Protein binding of cinacalcet is not affected by impaired hepatic function [see WARNINGS AND PRECAUTIONS and Use in Specific Populations].

Renal Impairment

The pharmacokinetic profile of a 75 mg Sensipar (cinacalcet) single dose in patients with mild, moderate, and severe renal impairment, and those on hemodialysis or peritoneal dialysis is comparable with that in healthy volunteers [see Use in Specific Populations].

Geriatric Patients

The pharmacokinetic profile of cinacalcet in geriatric patients (age ≥ 65 years, n = 12) is similar to that for patients who are < 65 years of age (n = 268) [see Use In Specific Populations].

Pediatric Patients

The pharmacokinetics of cinacalcet has not been studied in patients < 18 years of age [see Use In Specific Populations].

Clinical Studies

Secondary Hyperparathyroidism in Patients with Chronic Kidney Disease on Dialysis

Three 6-month, multicenter, randomized, double-blind, placebo-controlled clinical studies of similar design were conducted in patients with CKD on dialysis. A total of 665 patients were randomized to Sensipar (cinacalcet) and 471 patients to placebo. The mean age of the patients was 54 years, 62% were male, and 52% were Caucasian. The average baseline iPTH level by the Nichols intact immunoradiometric assay (IRMA) was 712 pg/mL, with 26% of the patients having a baseline iPTH level > 800 pg/mL. The mean baseline Ca x P ion product was 61 mg2/dL2. The average duration of dialysis prior to study enrollment was 67 months. Ninety-six percent of patients were on hemodialysis and 4% on peritoneal dialysis. At study entry, 66% of the patients were receiving vitamin D sterols and 93% were receiving phosphate binders. Sensipar (cinacalcet) (or placebo) was initiated at a dose of 30 mg once daily and titrated every 3 or 4 weeks to a maximum dose of 180 mg once daily to achieve an iPTH of ≤ 250 pg/mL. The dose was not increased if a patient had any of the following: iPTH ≤ 200 pg/mL, serum calcium < 7.8 mg/dL, or any symptoms of hypocalcemia. If a patient experienced symptoms of hypocalcemia or had a serum calcium < 8.4 mg/dL, calcium supplements and/or calcium-based phosphate binders could be increased. If these measures were insufficient, the vitamin D dose could be increased. Approximately 70% of patients in the Sensipar (cinacalcet) arm and 80% of the patients in the placebo arm completed the 6month studies. In the primary efficacy analysis, 40% of the patients on Sensipar (cinacalcet) and 5% of placebo-treated patients achieved an iPTH ≤ 250 pg/mL (p < 0.001) (Table 5, Figure 1). These studies showed that Sensipar (cinacalcet) reduced iPTH while lowering Ca x P, calcium, and phosphorus levels (Table 5, Figure 2). The median dose of Sensipar (cinacalcet) at the completion of the studies was 90 mg. Patients with milder disease typically required lower doses.

Similar results were observed when either the iPTH or biointact PTH (biPTH) assay was used to measure PTH levels in CKD patients on dialysis; treatment with cinacalcet did not alter the relationship between iPTH and biPTH.

Table 5. Effects of Sensipar (cinacalcet) on iPTH, Ca x P, Serum Calcium, and Serum Phosphorus in 6-month Phase 3 Studies (Patients on Dialysis)

Figure 1: Mean (SE) iPTH Values (Pooled Phase 3 Studies)

Data are presented for patients who completed the studies; Placebo (n = 342), Sensipar (cinacalcet) (n = 439).

Figure 2: Mean (SE) Ca x P Values (Pooled Phase 3 Studies)

Data are presented for patients who completed the studies; Placebo (n = 342), Sensipar (cinacalcet) (n = 439).

Reductions in iPTH and Ca x P were maintained for up to 12 months of treatment.

Sensipar (cinacalcet) decreased iPTH and Ca x P levels regardless of disease severity (i.e., baseline iPTH value), duration of dialysis, and whether or not vitamin D sterols were administered. Approximately 60% of patients with mild (iPTH ≥ 300 to ≤ 500 pg/mL), 41% with moderate (iPTH > 500 to 800 pg/mL), and 11% with severe (iPTH > 800 pg/mL) secondary HPT achieved a mean iPTH value of ≤ 250 pg/mL. Plasma iPTH levels were measured using the Nichols IRMA.

Parathyroid Carcinoma

Twenty-nine patients with parathyroid carcinoma were enrolled in a single-arm, open-label study. The study consisted of two phases, a dose-titration phase and a maintenance phase. Patients initially received 30 mg cinacalcet twice daily and then were titrated every 2 weeks to a maximum dose of 90 mg 4 times a day. Dosage escalation during the variable-length (2 to 16 weeks) titration phase continued until the serum calcium concentration was ≤ 10 mg/dL (2.5 mmol/L), the patient reached the highest possible dosage, or adverse events precluded further dosage increases.

Twenty-nine patients entered the study. The median exposure to cinacalcet was 229 days (range: 1 to 1,051). At baseline the mean (SE) serum calcium was 14.1 (0.4) mg/dL. At the end of the titration phase the mean (SE) serum calcium was 12.4 (0.5) mg/dL, which is a mean reduction of 1.7 (0.6) mg/dL from baseline. Figure 3 illustrates mean serum calcium (mg/dL) over time for all patients still on study at each time point from the beginning of titration to study visit week 80. Daily dose during the study ranged from 30 mg twice a day to 90 mg four times a day.

Figure 3: Serum Calcium Values in Patients With Parathyroid Carcinoma Receiving Sensipar (cinacalcet) at Baseline, Titration, and Maintenance Phase

n = Number of patients with non-missing values at the timepoint.

End of Titration (EOT) phase could occur at any visit from week 2 to 18. Patients at EOT are those who completed titration.

Patients with Severe Hypercalcemia Due to Primary Hyperparathyroidism

Seventeen patients with severe hypercalcemia due to primary HPT, who had failed or had contraindications to parathyroidectomy, participated in an open-label study. The study consisted of two phases, a dose-titration phase and a maintenance phase. In this trial severe hypercalcemia was defined as a screening serum calcium level of > 12.5 mg/dL. Patients initially received 30 mg cinacalcet twice daily and then were titrated every 2 weeks to a maximum dose of 90 mg 4 times a day. Dosage escalation during the variable-length (2 to 16 weeks) titration phase continued until the serum calcium concentration was ≤ 10 mg/dL (2.5 mmol/L), the patient reached the highest possible dosage, or adverse events precluded further dosage increases.

Seventeen patients entered the study. The median exposure to cinacalcet was 270 days (range: 32 to 1,105). At baseline the mean (SE) serum calcium was 12.7 (0.2) mg/dL. At the end of the titration phase the mean (SE) serum calcium was 10.4 (0.3) mg/dL, which is a mean reduction of 2.3 (0.3) mg/dL from baseline. Figure 4 illustrates mean serum calcium (mg/dL) over time for all patients still on study at each time point from the beginning of titration to study visit week 80. Daily dose during the study ranged from 30 mg twice a day to 90 mg four times a day.

Figure 4: Mean Serum Calcium (SE) at Baseline, End of Titration, and Scheduled Maintenance Visits (Patients with Severe intractable primary HPT)

n = Number of patients with non-missing values at the timepoint. End of Titration (EOT) phase could occur at any visit from week 2 to 18. Patients at EOT are those who completed titration.

Last reviewed on RxList: 4/19/2011
This monograph has been modified to include the generic and brand name in many instances.