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Monitoring Therapy and Summary
Since BMD changes correlate
well with fracture reduction in clinical trials of most antiresorptive agents,
BMD is used to monitor responses to therapy. Given the measurement precision
error of 1% for the spine and 1.5% for the hip, BMD changes must exceed 3% in
the spine or 4.5% in the hip to be considered significant. Since the maximum
rate of change even during periods of rapid gain, such as the first year of
bis-phosphonate therapy is 3% to 4% per year, it is necessary to wait at least
12 to 18 months between measurements to detect a meaningful BMD change in an
individual. Measuring biochemical markers of bone turnover is controversial
because of high variability, with a precision error of more than 20 %. However,
following markers is sometimes helpful because they change as much as 40% to
60% after only 3 months of treatment and predict changes in BMD at 1 to 2 years.50
In summary, we concur with a recent review 50 that the greatest reduction in fracture rates has been shown with bisphosphonates; they may be the best choice for women with the most severe disease (T scores < -2.5 and/or preexisting fractures). Alendronate, of the available bisphosphonates in the US also carries the most number of US-FDA approved indications, including treatment of osteoporosis in men. Estrogen’s effect on fracture rates may be of similar magnitude, although this has not yet been established in large randomized trials. Raloxifene might be especially useful in women who are interested in breast cancer risk reduction. Calcitonin is probably the least potent of the available agents, but may be useful in patients who do not tolerate other agents and in patients with acute vertebral compression fracture because of its analgesic effect. It may also be of some benefit in women who need to avoid bisphosphonates because of risk of esophageal injury, or avoid estrogen and/or raloxifene because of the risk of venous thromboembolism.
Evidence for combination therapies (such as alendronate and HRT) is mounting and most recently (April 2001) Canada approved this combination for treatment of osteoporosis in postmenopausal women. (See the section on Combination therapy under Ongoing Research.)
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