To evaluate the efficacy of etelcalcetide in reducing the iPTH level in children ages equal to or greater than 2 to less than 18 years with SHPT receiving maintenance hemodialysis.

Achievement of at least a 30% reduction from baseline in mean iPTH during the EAP (defined as weeks 20 through 27).

Percent Change from Baseline in Mean iPTH During EAP (defined as weeks 20 through 27).

Predialysis intact parathyroid hormone (iPTH) levels were measured by a central laboratory.

A serious adverse event is an AE that met at least 1 of the following criteria: * fatal * life threatening * required in-patient hospitalization or prolongation of existing hospitalization * resulted in persistent or significant disability/incapacity * congenital anomaly/birth defect * other medically important serious event. The relationship of each AE to study treatment was assessed by the investigator. The following AE grading scale was used: Mild: Transient or mild discomfort; no limitation in activity; no medical intervention/therapy required Moderate: Mild to moderate limitation in activity-some assistance may be needed; no or minimal medical intervention/therapy required Severe: Marked limitation in activity, some assistance usually required; medical intervention/therapy required, hospitalization possible Life-threatening: Extreme limitation in activity, significant assistance required, significant medical intervention/therapy required, hospitalization probable.

Treatment-related adverse events are those the investigator indicated as having a reasonable possibility of having been caused by etelcalcetide. A serious adverse event is defined as an adverse event that meets at least 1 of the following serious criteria: • fatal • life threatening • requires in-patient hospitalization or prolongation of existing hospitalization • results in persistent or significant disability/incapacity • congenital anomaly/birth defect • other medically important serious event.

Laboratory toxicity grading was based on Common Terminology Criteria for Adverse Events (CTCAE) version 4.0, where Grade 0 represents values in the normal range and grade 4 represents values with life-threatening consequences and urgent intervention indicated.

A validated dual flow-cell biosensor immunoassay was used to detect antibodies capable of binding etelcalcetide. The number of participants with a negative or no result at baseline and positive binding antibodies at any time post-baseline is reported.

Blood pressure (BP) values were taken post-hemodialysis assessments.

Participants who did not have any scheduled assessments during the EAP were considered non-responders.

Participants who did not have any scheduled assessments during the EAP were considered non-responders.

The changes in T50 values between the different study phases will be evaluated as the primary outcome.

Tmax is the time to maximum drug concentration of plasma etelcalcetide after dosing on Days 1 and 27.

Cmax was defined as the maximum observed plasma drug concentration measured between the time of drug administration to the beginning of the next dialysis session.

AUClast was specifically defined in this study as the area under the concentration time curve measured from the time of drug administration to the beginning of the next dialysis session, following the first and last dose.

Accumulation ratio, calculated as AUClast day 27/AUClast day 1.

A treatment-emergent adverse event is any adverse event (AE) that begins or worsens after the initial dose of study drug (etelcalcetide) and up to 30 days after the last dose. Common adverse events were defined as adverse events occurring in at least 2 participants. The Medical Dictionary for Regulatory Activities (MedDRA) version 21.0 was used for coding all adverse events.

When albumin was less than 4.0 mg/dL, the calcium concentration was corrected according to the formula: cCa (mmol/L) = measured total serum calcium (mmol/L) + 0.02 (40 - serum albumin \[g/L\]).

The total radioactivity in excreta (urine and feces) or dialysate and dialysis membrane is expressed as a percentage of the total radioactive \[¹⁴C\] administered (dose). Total radioactive counts in dialysate, dialyzer, feces, and urine were determined by accelerator mass spectrometry (AMS). Radioactivity excreted during non-sampled days was estimated by interpolation and extrapolation of the measured data.

Total radioactive counts in plasma was determined by accelerator mass spectrometry (AMS).

Etelcalcetide plasma concentrations were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Etelcalcetide plasma concentrations were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS).