Etelcalcetide for Secondary Hyperparathyroidism in Children

Inclusion Criteria: * Participant's legally acceptable representative has provided informed consent when the participant is legally too young to provide informed consent and the participant has provided written assent based on local regulations and/or guidelines prior to any trial-specific activities/procedures being initiated. * Male or female participants greater than or equal to 2 to less than 18 years of age at the time of enrollment. * Targeted dry weight greater than or equal to 7 kg at the time of screening Week -1. * Diagnosed with CKD and SHPT undergoing hemodialysis/hemodiafiltration TIW or four times a week (QIW) at the time of screening greater than or equal to 1 month. * Diagnosis of SHPT with the mean of the 2 consecutive central laboratory iPTH values greater than 300 pg/mL during screening, on separate days and within 2 weeks of enrollment obtained from the central laboratory during screening. * Serum corrected Ca value greater than or equal to 9.0 mg/dL obtained from the central laboratory during screening. * Dialysate Ca level greater than or equal to 2.5 mEq/L for at least 1 month prior to screening and throughout the duration of the trial. * participant receiving active vitamin D sterols must have had no more than a maximum dose change of 50% within the 2 weeks prior to screening laboratory assessments, remain stable through enrollment, and be expected to maintain stable doses for the duration of the trial, except for adjustments allowed per protocol. * participant receiving phosphate binders must have had no more than a maximum dose change of 50% within the 2 weeks prior to screening laboratory assessments, remain stable through enrollment, and be expected to maintain stable dose for the duration of the trial, except for adjustments allowed per protocol. * Subject receiving Ca supplements must have had no more than a maximum dose change of 50% within the 2 weeks prior to screening laboratory assessments, remain stable through enrollment, and be expected to maintain stable dose for the duration of the trial, except for adjustments allowed per protocol. * SHPT not due to vitamin D deficiency, per investigator assessment. Exclusion Criteria: * Disease Related: * History of congenital long QT syndrome, second or third degree heart block, ventricular tachyarrhythmia's, history of symptomatic ventricular dysrhythmias Torsades de Pointes or other conditions associated with prolonged QT interval. * Anticipated or scheduled parathyroidectomy during the trial period. * Anticipated or scheduled kidney transplant during the trial period. * Participant has received a parathyroidectomy within 6 months prior to enrollment. * Other Medical Conditions: * Current malignancy or history of other malignancy, except non-melanoma skin cancers within the last 5 years. * Prior/Concomitant Therapy: * Use of concomitant medications that may prolong the QTc (eg, ondansetron, albuterol, sotalol, amiodarone, erythromycin, or clarithromycin). Refer to CredibleMeds.org for guidance. Certain medications may be allowed based on review by the Medical Monitor and require additional electrocardiogram (ECG) monitoring and potential electrolyte monitoring. * Receipt of cinacalcet therapy within 30 days prior to screening and through enrollment. * Any previous use of etelcalcetide prior to screening and through enrollment (Original protocol, Amendment 1, and Amendment 2 only). * Receipt of etelcalcetide therapy within 6 months prior to screening assessments and through enrollment (Amendment 3 and later only). * All herbal medicines (eg, St. John's wort), vitamins, and supplements consumed by the participant within the 30 days prior to enrollment, and continuing use if applicable, will be reviewed by the Principal Investigator and the Amgen Medical Monitor. Written documentation of the review and Amgen acknowledgment is required for participant participation. * Use of any over-the-counter or prescription medications within the 14 days or 5 half-lives (whichever is longer) prior to enrollment that are not established therapies for participants with renal disease or other conditions secondary to renal disease will be reviewed by the Principal Investigator and the Amgen Medical Monitor. Written documentation of the review and Amgen acknowledgment is required for participant participation. Paracetamol for analgesia will be allowed. * Prior/Concurrent Clinical Trial Experience: * Currently receiving treatment in another investigational device or drug trial, or less than 30 days since ending treatment on another investigational device or drug trial(s). Other investigational procedures while participating in this trial are excluded. * Diagnostic Assessments During Screening: * Participant has significant abnormalities on the most recent central laboratory test during the screening period prior to enrollment per the Investigator including but not limited to the following: a. Serum transaminase (alanine aminotransferase \[ALT\] or serum glutamic pyruvic transaminase \[SGPT\], aspartate aminotransferase \[AST\], or serum glutamic oxaloacetic transaminase \[SGOT\]) greater than 1.5 times the upper limit of normal (ULN). * Corrected QT interval greater than 500 ms, using Bazett's formula. * Corrected QT interval greater than or equal to 450 to less than or equal to 500 ms, using Bazett's formula, unless written permission to enroll is provided by the investigator after consultation with a pediatric cardiologist. * Participant has a clinically significant ECG abnormality (eg, unstable arrhythmia) during screening that, in the opinion of the investigator, could pose a risk to participant safety or interfere with the trial evaluation. * Within the 3 Months Prior to Screening: * New onset or worsening of a pre-existing seizure disorder. * Participants on anti-convulsant medication must be on a stable and therapeutic dose for 3 months prior to screening (if blood level monitoring is clinically available, then the participant must have a therapeutic blood level within 1 week of enrollment). Other Exclusions: * Female participant is pregnant or breastfeeding or planning to become pregnant or breastfeed during treatment and for an additional 3 months after the last dose of etelcalcetide. (Females of childbearing potential should only be included in the trial after a confirmed menstrual period and a negative highly sensitive serum pregnancy test within 7 days prior to the first dose of investigational product). * Female participants of childbearing potential unwilling to use 1 highly effective or acceptable method of effective contraception during treatment and for an additional 3 months after the last dose of investigational product. * Female participants of childbearing potential with a positive pregnancy test assessed at screening by a serum pregnancy test. * Participant has known sensitivity to etelcalcetide or excipients to be administered during dosing. * Participant likely to not be available to complete all protocol-required trial visits or procedures, and/or to comply with all required trial procedures to the best of the participant and investigator's knowledge. * History or evidence of any other clinically significant disorder, condition or disease (with the exception of those outlined above) or unacceptable physical findings, that, in the opinion of the investigator or Amgen physician, if consulted, would pose a risk to participant safety or interfere with the trial evaluation procedures or completion. * Participant has previously entered this trial or previously received treatment with etelcalcetide (Original protocol, Amendment 1 and Amendment 2 only). * Participant previously has entered this trial (Amendment 3 and later only). * Anemia, which in the opinion of the investigator makes it not advisable to undergo sequential blood draws. * History of unstable chronic heart failure within the last 1 year prior to screening.