- Design
- Analysis of a randomised trial of three oral bisphosphonates
- Population
- 108 postmenopausal women under 85
- Primary outcome
- Performance of BMD and bone turnover markers as response monitors
- Effect
- Response detected in 96% (CTX) and 94% (PINP) vs 47% (spine BMD)
This analysis used data from 108 postmenopausal women randomised to two years of alendronate, ibandronate or risedronate with calcium and vitamin D, to compare ways of monitoring response.
Bone turnover markers had a much stronger signal than bone density. Using the conventional least significant change, 96% (CTX) and 94% (PINP) of women showed a response within three months, against 47% at the spine and 24% at the hip on two-year DXA. The authors propose an 'expected change' threshold, met by 90% of adherent patients, which worked for CTX and PINP but not for bone density.
Non-adherence to oral bisphosphonates is common, and waiting two years for a repeat DXA to find out is slow and insensitive. A fasting CTX or PINP at baseline and three months offers an early check that the drug is being taken and absorbed.
- Measure fasting morning CTX or PINP before starting an oral bisphosphonate
- Repeat the same marker at about three months
- Review adherence and dosing technique if the fall is smaller than expected
- Do not rely on a two-year DXA alone to judge whether treatment is working
- Use the same laboratory for both samples
Why it matters
Many patients on oral bisphosphonates are not taking them properly, and bone density takes years to show it.
Don't overread it
Based on 108 women in trial conditions; the expected-change thresholds need testing in routine practice.
The statistics, in plain English
A higher signal-to-noise ratio means a real change is easier to tell from measurement noise. CTX and PINP were two to five times better than bone density on this measure.
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