Bisphosphonates

Bisphosphonates are stable analogues of pyrophosphate which bind to, and stabilise, bone by inhibiting osteoclastic activity. Bisphosphonates may also directly stimulate formation of bone by osteoblasts (1).

The main indications for bisphosphonates are:

• Paget's disease of bone
• hypercalcaemia of malignancy
• osteoporosis

Bisphosphonates are poorly absorbed after oral ingestion. Further impairment to absorption is caused by food, drinks and drugs containing magnesium, calcium, iron or aluminium salts.

A proportion of bisphosphonate that are absorbed is taken up by, and incorporated into, bone while the remaining fraction is excreted unchanged by the kidneys. Bisphosphonates that have been taken up and incorporated into the skeleton are then only released when the bone is resorbed during turnover.

The oral bisphosphonate medicines prescribed in the UK are:

• alendronate
• sodium clodronate
• disodium etidronate
• ibandronate
• risedronate sodium
• disodium tiludronate

The intravenous/injected bisphosphonates prescribed in the UK are:

• sodium clodronate
• ibandronate
• disodium pamidronate
• zoledronic acid (2)

Reference:

• (1) Drugs and Therapeutics Bulletin (2001), 39 (9), 68-72.
• (2) Medicines and Healthcare products Regulatory Agency (MHRA) 2011. Bisphosphonates