Bisphosphonates are first-line drugs used to treat a wide range of bone disorders, including:

  • Osteoporotic fragility fractures
  • Paget’s disease of bone
  • Certain cancers – where they are used to prevent pathological fractures

Bisphosphonates are easily identifiable drugs, too. They all contain either of the following two suffixes – –dronate or –dronic acid.

Mechanism of Action

Bisphosphonates act on bone – where they inhibit cells called osteoclasts.

The function of osteoclasts is to break down bone, an essential function for the bone maintenance and repair. However, in diseases such as osteoporosis, osteoclasts can play a pathological role and so, by intervening in how osteoclasts work, it can reduce bone loss and improve bone mass.

Bisphosphonates have a similar structure to naturally occurring pyrophosphate and so are readily absorbed into bone. There, bisphosphonates accumulate in osteoclast cells – triggering cell death. Fewer osteoclast cells lead to reduced bone turnover and an increase in bone mass and reduction in bone loss.

Side Effects

One of the most common side effects of orally administered bisphosphonates is esophagitis – or inflammation of the esophagus. To reduce the risk of esophagitis, patients are counseled to take bisphosphonates in a more cautionary manner compared to other drug classes.

Patients are counselled to take these drugs whilst remaining upright, first thing in the morning and 30 minutes before food/medicines and taken with a full glass of water. Patients should remain upright for 30-minutes post-administration. By taking these steps, the risk of esophagitis or irritation to the esophagus, is substantially reduced.

Other side effects of bisphosphonates include:

  • Hypophosphatemia – low blood phosphorus levels
  • Osteonecrosis of the jaw – a rare effect associated with high-dose IV therapy
  • Atypical femoral fracture
  • Headache
  • Constipation
  • Nausea

Bisphosphonates may also be associated with other side effects not listed in this guide.

Source – PTCB guide to pharmacology

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