Alendronate (Fosamax®) and Risedronate (Actonel®)

Alendronate and risedronate are closely related medications that are Food and Drug Administration (FDA)-approved to reduce risk of fracture in those with osteoporosis, or other states associated with a high risk of fracture. Both agents are also used to treat Paget’s disease of the bone. These agents work in nearly identical ways.

After being absorbed into the blood stream, they both bind very tightly to bone, where they inhibit the action of bone cells called osteoclasts. Osteoclasts are bone cells responsible for removing mineral and bone protein from bones so they become thinner and structurally weaker, and meaning they break more easily with minor trauma such as a fall on a loose rug or ice. By reducing the activity of osteoclasts, alendronate and risedronate allow cells that build bone to "catch up" and replace some of the bone osteoclasts have removed.

For osteoporosis, the standard full dose of alendronate proven to reduce risk of fractures is 70 mg once a week. The standard full dose of risedronate proven to reduce risk of fractures is 35 mg once weekly.

A half-dose tablet of alendronate is available (35 mg once weekly), if the primary purpose is to prevent further bone loss rather than optimally reduce fracture risk.

For Paget’s disease of bone, the usual doses are alendronate at 40 mg once a day for up to six months, or risedronate at 30 mg once a day up to six months.

The most common side effect with alendronate and risedronate is stomach upset, which occurs in one out of five to one out of 10 people.

Irritation or rarely an ulcer of the esophagus may occur. The risk of injury to the esophagus is increased if the person taking the medicine has uncontrolled heartburn or a narrowing of the esophagus (called a stricture) that interferes with passage of food or pills into the stomach.

There may be a very slight increased risk of stomach ulcers from these medicines if they are taken with anti-inflammatory medications, such as aspirin or ibuprofen.

Some people infrequently or rarely experience pain in their limbs (from bone or muscle) while on these medications.

Low blood calcium (hypocalcemia) can, but rarely occurs, especially if calcium or vitamin D intake is low.

Alendronate and risedronate improve bone density gradually, about 5 percent to 10 percent in the spine over three to five years, and 3 to 5 percent in the hip over that same time frame. After three years of use, both drugs tend to maintain bone density rather than increase it further.

The risk of fractures is not reduced immediately with use of these drugs, but spine fracture risk is reduced within six months of starting these medicines. Reducing hip, wrist or other nonspine fracture risk takes longer.

Both drugs fairly tightly to bone – especially alendronate. Therefore, some protection against fractures may persist after stopping the drug, especially if it has been used for several years.

In Paget’s disease, markers of disease activity, such as the blood level of alkaline phosphatase gradually lessen over a few months. Bone pain associated with Paget’s disease subsides in three to six months.

No laboratory tests to monitor for side effects are needed. Typically, a repeat bone mineral density test is done two years after commencement of alendronate or risedronate to reveal the degree to which bone density has improved.

Both alendronate and risedronate are poorly absorbed from the intestine into the blood stream, and other medicines, food and supplements can prevent absorption of alendronate and risedronate altogether. Therefore, each dose of alendronate or risedronate should be taken with a full glass of water on an empty stomach. We advise waiting a full hour after each dose before having anything else to eat or drink except water, and before taking other medications or supplements.

It is important not to lie down for at least an hour after taking alendronate or risedronate, to reduce the risk of esophageal upset or injury as much as possible.

It is very important that those on alendronate or risedronate be getting adequate amounts of calcium and vitamin D through their diet or supplements. Inadequate amounts of daily calcium or vitamin D may blunt the benefit from these medicines.