Palopegteriparatide is a long-acting parathyroid hormone analog and prodrug of PTH(1-34) developed as a hormone-replacement therapy for adults with hypoparathyroidism. It is the active substance in YORVIPATH, a once-daily subcutaneous injectable product. The U.S. FDA approved YORVIPATH in 2024, while the European Medicines Agency approved it for chronic hypoparathyroidism in adults in 2023.
Palopegteriparatide is structurally different from conventional low-molecular-weight pharmaceutical ingredients. It consists of the biologically active N-terminal PTH(1-34) peptide transiently conjugated to a branched methoxypolyethylene glycol (mPEG) carrier through a proprietary cleavable TransCon Linker. The FDA describes the carrier as a branched 40 kDa, or 2 × 20 kDa, mPEG moiety. The average molecular weight of the complete drug substance is approximately 47.4 kDa.
The internationally recognized substance is:
FDA's Substance Registration System identifies CAS 2222514-07-8 and UNII G2N64C3385 for palopegteriparatide.
Palopegteriparatide is a PEGylated peptide prodrug rather than a discrete conventional molecular structure. FDA gives the theoretical molecular formula as:
C209H340N60O59S3 + 2 × (C2H4O)n
where n is approximately 450–500. Because the PEG component has a polymeric distribution, a single fixed molecular formula and exact molecular weight are not appropriate in the same manner as for a conventional small molecule. The FDA therefore describes the drug substance using an average molecular weight of approximately 47.4 kDa.
The FDA GSRS record also reports an estimated average molecular weight of approximately 4,120 Da for a different substance representation, illustrating why the complete conjugated drug substance should be characterized using its defined polymer/peptide architecture rather than relying on a simple small-molecule molecular-weight entry.
Palopegteriparatide contains PTH(1-34), the first 34 amino acids of human parathyroid hormone. This N-terminal region contains the biologically active portion responsible for PTH receptor activity.
Teriparatide/PTH(1-34) has the sequence:
SVSEIQLMHNLGKHLNSMERVEWLRKKLQDVHNF
The peptide contains 34 amino acids and has a molecular weight of approximately 4.12 kDa. PubChem identifies teriparatide/PTH(1-34) with CAS 52232-67-4.
Palopegteriparatide modifies this peptide through N-terminal conjugation to the TransCon PEG-linker system. The conjugate is designed to provide controlled release of active PTH(1-34) following administration.
Palopegteriparatide functions as a prodrug of PTH(1-34). Under physiological conditions, the PTH peptide is gradually cleaved from the PEG-containing prodrug, producing sustained systemic exposure to active PTH.
Released PTH(1-34) activates the parathyroid hormone 1 receptor (PTH1R). PTH1R signaling regulates calcium and phosphate homeostasis through effects on bone and kidney.
The pharmacological actions include:
The EMA describes palopegteriparatide as a PTH replacement therapy and states that the released PTH(1-34) and its principal metabolite PTH(1-33) have similar affinity for and activation of PTH1R compared with endogenous PTH.
The primary approved therapeutic application of palopegteriparatide is chronic hypoparathyroidism in adults.
Hypoparathyroidism is characterized by inadequate secretion or activity of parathyroid hormone, resulting in disturbances of calcium and phosphate metabolism. Conventional management can require calcium supplementation and active vitamin D.
YORVIPATH provides a replacement approach by delivering a long-acting PTH analog designed to provide sustained exposure to active PTH. The current FDA indication is treatment of hypoparathyroidism in adults.
The EMA similarly identifies Yorvipath as a PTH replacement therapy for adults with chronic hypoparathyroidism.
The current U.S. FDA label specifies individualized once-daily subcutaneous dosing. The maximum recommended dose is 30 mcg once daily. Available prefilled-pen presentations include:
The dosage is individualized according to serum calcium.
Palopegteriparatide is particularly relevant to pharmaceutical and biotechnology development involving:
The compound is classified as a peptide and is recognized as an approved drug by both EMA and FDA.
Palopegteriparatide uses the TransCon approach, in which the active peptide is temporarily conjugated to a large PEG carrier through a cleavable linker.
This design provides a distinction between:
Prodrug form: Palopegteriparatide
Released active hormone: PTH(1-34)
The objective is controlled liberation of active PTH over time rather than immediate exposure following administration. This supports once-daily dosing while maintaining sustained systemic PTH exposure.
Because palopegteriparatide is a complex peptide-polymer conjugate, its characterization requires analytical techniques appropriate for biologics and polymer-conjugated peptides.
Potential characterization approaches include:
A conventional single-number HPLC assay percentage should not be assumed to represent the complete quality characterization of this drug substance.
For a complex peptide-polymer drug substance, quality control should consider multiple critical quality attributes rather than only assay and impurities.
Important quality characteristics include:
The FDA's original review specifically discusses chemistry, manufacturing and controls for palopegteriparatide and identifies delivered dose as an important product quality attribute.
The marketed product is supplied as a sterile, clear and colorless solution in a glass cartridge incorporated into a single-patient-use prefilled pen for subcutaneous administration.
The FDA labeling specifies that the product should not be frozen and should be protected from light. After first use, the pen is refrigerated at 2–8°C.
These conditions apply to the finished medicinal product and should not automatically be transferred to an isolated API/drug-substance specification.
Palopegteriparatide is an approved pharmaceutical substance.
The EMA lists Yorvipath as an orphan medicine and under additional monitoring.
Palopegteriparatide is a specialized peptide-polymer drug substance requiring advanced pharmaceutical manufacturing and analytical capabilities. Manufacturing programs should incorporate appropriate controls for peptide synthesis, conjugation, PEG characterization, purification, sterile product processing where applicable, analytical characterization and stability.
For pharmaceutical qualification, supporting documentation can include:
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.2% |
| Individual Impurity | ≤ 0.5% |
| Total Impurities | ≤ 1.5% |
| Water Content | NMT 1.0% |
| Melting Point | Approximately 184–185°C |