Bisphosphonates

Bisphosphonates are pyrophosphate analogs that bind tightly to hydroxyapatite and gather where osteoclasts are resorbing bone. Osteoclasts take them up as they work; alendronic and zoledronic acid then block farnesyl pyrophosphate synthase, so small GTPase signaling proteins go unprenylated and the cells stop resorbing or die. Bone turnover falls and bone density slowly rises.

• Alendronic acidUsually taken once a week. Because it stays in bone for years, the need to continue is reviewed after 3 to 5 years, and people at low fracture risk may stop or take a break.
• Zoledronic acidFor osteoporosis one infusion covers a whole year; in cancer care it is given far more often, and osteonecrosis of the jaw is then more common.

• Osteoporosis, to lower the risk of fractures
• Paget's disease of bone
• High calcium caused by cancer
• Bone metastases from solid tumors
• Bone disease in multiple myeloma

• Esophagitis and esophageal ulcers (tablets)Known forSerious
• Osteonecrosis of the jawKnown forSerious
• Atypical thigh-bone (femur) fracturesKnown forSerious
• Low calcium (hypocalcemia)Serious
• Flu-like reaction with fever after an infusion
• Kidney injury, mainly with intravenous infusionsSerious
• Bone, joint or muscle pain, sometimes severe
• Eye inflammation: uveitis or scleritisSerious
• Indigestion, acid reflux and abdominal pain
• Worse asthma, mainly in aspirin-sensitive peopleSerious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Tablets are taken on waking with a full glass of plain water, followed by 30 minutes upright with nothing else by mouth.
• Correct low calcium and vitamin D deficiency first, and keep calcium and vitamin D intake adequate.
• Avoid when creatinine clearance is below 35 mL/min; infusions need good hydration and a creatinine check each time.
• Check the teeth before starting and avoid invasive dental work where possible; review the need to continue after 3 to 5 years.

Written for biofideX in plain words, after checking these references:

• Bisphosphonate (NCI Thesaurus)
• Alendronate sodium tablets: label (DailyMed)
• Zoledronic acid injection for osteoporosis and Paget's disease: label (DailyMed)
• Zoledronic acid injection for cancer-related bone disease: label (DailyMed)
• Alendronic acid (NCI Thesaurus)
• Side effects of alendronic acid (NHS)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.