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Bisphosphonates (BPs) are the medications most commonly prescribed to treat osteoporosis. They prevent bone loss and reduce the risk of fractures.

How they work

These drugs are similar to a natural bone material called pyrophosphate. BPs are similar enough to bind strongly to existing bone and become embedded in the skeleton. They prevent further bone loss and create a "protective layer" that slows down osteoclast activity from dissolving tissue on the bone's surface.

Bisphosphonates available in Canada
The bisphosphonates available in Canada include:

  • Etidronate (available as Didronel® or, when supplemented with calcium carbonate, Didrocal®) – approved for the prevention and treatment of post-menopausal osteoporosis. Etidronate is taken on a cyclical basis, ie. for two weeks out of every three-month period.
  • Alendronate (Fosamax®) – approved for the prevention and treatment of post-menopausal osteoporosis.
  • Risedronate (available as Actonel®) – approved for the prevention and treatment of post-menopausal osteoporosis. Risedronate is also available with calcium.
  • Zoledronic acid (Aclasta®, known as Reclast® in the U.S.) – approved by Health Canada in 2007 for the treatment of osteoporosis in post-menopausal women. This prescription medication is purchased by the patient and then administered by a health professional intravenously, for 15 minutes once a year.

How effective are bisphosphonates?
All four BPs have the potential to slow down bone loss and increase bone density. These medications have the potential to reduce the risk of fractures for both men and women who have osteoporosis.

Alendronate (Fosamax), risedronate (Actonel) and zolendric acid have all been shown to significantly reduce a woman’s risk of fracture in the spine, hip and other bones. Etidronate is the least effective of the four drugs.

Place in osteoporosis therapy
With the emerging data about the effectiveness of the newer BPs, alendronate and risedronate are now considered "first-line" agents for the treatment of post-menopausal osteoporosis.

How to take BPs

Some bisphosphonates (BPs) are taken orally – once a day, twice a week, once a week, or once a month. Zoledronic acid is given intravenously (by IV) once a year.

The stomach does not absorb etidronate, alendronate or risedronate well. These drugs can interact with minerals, such as calcium, magnesium, aluminum and iron, as well as many substances in food and drink, and in other medications, which can prevent the BPs from getting absorbed.

For this reason, all oral BPs must be taken alone, on an empty stomach first thing in the morning, with a full glass of water. It is important to stay in an upright position (standing or sitting, not bending over or lying down) and refrain from eating or drinking anything but water for at least 30 minutes after taking one of these medications.

Your doctor and pharmacist will tell you exactly how to take your particular BP – the instructions will include information about food, beverages, vitamin and mineral supplements, and other medications.  

The side-effects of oral BPs vary from medication to medication, but may include:

  • headache
  • difficulty swallowing
  • heartburn
  • upset stomach
  • nausea
  • abdominal pain
  • inflamed esophagus
  • gastric ulcers
  • gas and bloating
  • diarrhea

These can occur when you start taking the medication, but usually go away as your stomach gets used to them.

Rare side-effects include:

  • changes in taste (for example, a metallic taste)
  • pain in the muscles, joints and/or bone
  • rash
  • dizziness
  • dry eyes
  • ringing in the ears
  • swollen feet or lower legs
  • feeling of weakness

The side-effects of intravenous BPs can include:

  • fever and other flu-like symptoms
  • pain in the muscles and/or joints
  • headache

Rare side-effects of some oral BPs (such as alendronate) and intravenous BPs include:

  • vision disturbances and blurred vision
  • osteonecrosis of the jaw (rotting of the jawbone) – affects 1/10,000-1/100,000 patients taking oral BPs for osteoporosis

If you are taking a BP, inform both your doctor and your dentist if you are going to have an invasive dental procedure or if you have a wound with exposed bone in your mouth.


BPs are expensive medications. Before having a prescription filled, check to find out whether your insurance company and/or provincial health plan covers the cost. Coverage varies from province to province.

To find out which osteoporosis drugs are covered in your province, click here to visit the Osteoporosis Canada website.


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  • A publication of:
  • Women's College Hospital