Parathyroid hormone (rhPTH 1-84)

How it works

It replaces endogenous parathyroid hormone, raising serum calcium by increasing renal tubular calcium reabsorption, promoting renal activation of vitamin D and enhancing calcium release from bone.

Prescribing in practice

• Because of a theoretical osteosarcoma risk seen with parathyroid hormone analogues in animal studies, use is generally avoided in patients at increased risk of osteosarcoma, such as those with prior skeletal radiotherapy or unexplained raised alkaline phosphatase.
• It is an adjunct to, not a replacement for, calcium and active vitamin D, and these should be titrated together to avoid hyper- or hypocalcaemia.
• Abrupt discontinuation can precipitate severe hypocalcaemia, so stopping requires reinstatement or up-titration of conventional therapy.

Monitoring

Monitor serum and urinary calcium, renal function and vitamin D status, particularly during initiation and any dose adjustment of background therapy.

Counselling the patient

• Report symptoms of low calcium such as tingling around the mouth, muscle cramps or spasms.
• Do not stop the injection suddenly without medical advice, as calcium levels can fall dangerously.
• Keep all scheduled blood test appointments so calcium can be tracked.

Evidence & guidelines

Its use in chronic hypoparathyroidism is supported by the SPC and regulatory approval as adjunctive therapy when conventional treatment is insufficient.