This page contains additional information about the article Strontium ranelate (Protos) for postmenopausal osteoporosis, published in NPS RADAR, November 2007.
Women enrolled in TROPOS probably had a higher risk of fracture than those in FIT-2 because of the mixture of primary and secondary prevention populations, and the fact that they were older and had lower average BMD (see Table 1). In TROPOS, 55% had a previous fracture, however, only 71% of the whole population were X-rayed for vertebral fracture, hence the exact proportion is unknown. These factors may explain why the absolute risk of fracture differs between TROPOS and FIT-2, as seen by comparing the placebo fracture event rates* (6.4% strontium; 2.2% alendronate). Though not identical, women in SOTI and FIT-1 showed more similarity in baseline fracture risk (see Table 2).14,16
* The validity of an indirect comparison depends on the included trials being similar (assuming each trial is internally valid) because the drug's absolute treatment effects (defined by the absolute risk reduction or number needed to treat) are influenced by baseline risk.
Table 1 Key characteristics of the TROPOS13 and FIT-215 trials (used for primary prevention comparison)
TROPOS | FIT-2 (primary prevention) | |
---|---|---|
Baseline risk |
|
|
Vertebral X-ray before randomising | No |
Yes |
Number of women | 4932 | 4432 |
Completed follow-up | 3320 (67%) | 4134 (93%) |
Mean age | 77 years | 68 years |
Study centres | 11 European countries and Australia | 11 metropolitan areas of the United States |
Intervention | Strontium (either 2 g once daily or 1 g twice daily) versus placebo for 3 years | Alendronate 5 mg daily for 2 years then 10 mg daily versus placebo for 4 years |
Primary outcome | New non-vertebral fracture (excluding skull, face, finger, toe and coccyx) as diagnosed by a physician | One or more clinical fractures — pre-specified as vertebral, non-vertebral, hip, wrist and 'other' (excluding face or skull) as diagnosed by a physician |
Secondary outcomes | Study not powered for these outcomes | Study not powered for this outcome |
TROPOS = Treatment of Peripheral Osteoporosis study13 FIT-2 = Fracture Intervention Trial15 |
Table 2 Key characteristics of the SOTI14 and FIT-116 trials (used for secondary prevention comparison)
SOTI | FIT-1 (secondary prevention) | |
---|---|---|
Baseline risk |
In addition to one baseline vertebral fracture:
|
In addition to one baseline vertebral fracture:
|
Number of women | 1442 | 2027 |
Completed follow-up | 1260 (87%) | 1946 (96%) |
Mean age | 70 years | 71 years |
Study centres | 11 European countries and Australia | 11 metropolitan areas of the United States |
Intervention | Strontium (either 2 g once daily or 1 g twice daily) versus placebo for 3 years | Alendronate 5 mg daily for 2 years then 10 mg daily versus placebo for 3 years |
Primary outcome | New radiographic or clinical vertebral fracture | New radiographic vertebral fractures |
Secondary outcomes | Study not powered for this outcome | Study powered for this outcome |
SOTI = Spinal Osteoporosis Therapeutic Intervention study14 FIT-1 = Fracture Intervention Trial16 |