Bisphosphonates for prevention of postmenopausal osteoporosis

Our studies showed that 5 mg alendronate per day was the lowest, most effective dose that persistently prevented bone loss in recently postmenopausal women with normal bone mass. The effect on bone mass and biochemical markers was found comparable to that of commonly recommended regimens of postmenopausal HRT, and 5 mg alendronate per day is suggested as a new option for prevention of postmenopausal osteoporosis. HRT must, however, still be considered the first choice for this indication because of additional beneficial effects on other organ systems. The effect of alendronate was unaffected by bone or fat mass status, but increased with increasing postmenopausal age. The implications were that alendronate stabilized bone mass to a comparable extent in women at particular risk of osteoporosis because of thin body habitus or low bone mass and in healthy postmenopausal women with normal bone mass. Calcium supplementation was insufficient to prevent bone loss and did not add an effect on bone metabolism when combined with alendronate treatment in recently postmenopausal women. The gastrointestinal risk and adverse event profile of 5 mg alendronate per day was comparable to that of placebo, and this dose of alendronate appeared safe for long-term use. Bone loss resumed at a normal postmenopausal rate promptly after withdrawal of alendronate in early postmenopausal women consistent with a substantial underlying natural bone loss during early menopause. Oral ibandronate increased bone mass at all skeletal regions in elderly postmenopausal women with low bone mass, and 2.5 mg ibandronate per day was the lowest dose with this effect. The results are indicative of ibandronate as an option for secondary prevention of postmenopausal osteoporosis, but longer-term phase III trials should be performed before ibandronate can be recommended for this indication. The study showed that 2.5 mg ibandronate per day was efficient for prevention of bone loss and increment in bone mass in a population of women at particular risk of osteoporosis because of low bone mass. There were no differences between 2.5 mg ibandronate per day and placebo in terms of side effects, including complaints from the gastrointestinal tract, and ibandronate appeared safe for longer-term use in this dosing. Bone loss resumed at a normal postmenopausal rate when treatment was withdrawn. The response in bone mass and biochemical markers indicated that 2.5 mg ibandronate per day is equivalent to 10 mg alendronate per day in postmenopausal women. Our studies of two recently developed biochemical markers, urine CTX and serum total OC, showed that bone turnover was lowest in the premenopausal period, where these biochemical markers furthermore revealed a negative association with bone mass. It indicated that increased bone turnover contributes to a small premenopausal bone loss and resulting lowered bone mass. In consistence, a small premenopausal bone loss was observed in some regions of the hip. The biochemical markers increased at the time of menopause, consistent with initiation of the postmenopausal bone loss, and became gradually more negatively associated with bone mass as time past the menopause increased. The biochemical markers were furthermore higher in postmenopausal women with low bone mass, consistent with the characterization of postmenopausal osteoporosis as a condition with increased bone turnover. Our results consistently indicated a central role of increased bone turnover for development of low bone mass and osteoporosis. It is, however, also important to stress that the associations between biochemical markers and bone mass were too weak to allow for a valid individual estimation of bone mass based on biochemical markers. In contrast, the biochemical markers were shown as valid tools for monitoring and prediction of treatment effect of bisphosphonates. CTX, NTX, and total OC revealed the best performance characteristics in this respect. Six months after start of treatment, the level of suppression of these biochemical markers of bone resorption and formation accurately reflected the size of the 1-2 year response in bone mass in groups of women treated with bisphosphonate. This was a clear advance over bone densitometry, which has a precision error in the area of the anticipated yearly bone mass response during bisphosphonate therapy. The relationship was consistent during treatment with alendronate or ibandronate and in younger or elderly postmenopausal women. In individual patients, cut-off values of an about 40% decrease in urine CTX or NTX and an about 20% decrease in total OC validly predicted long-term prevention of bone loss. The sensitivity of prediction was high, but the specificity low. This implicated that the biochemical markers could be used as an exact method to detect "responders" to therapy, whereas "non-responders" to bisphosphonate treatment should be detected with bone densitometry in patients who do not reveal a decrease below the cut-off value in the biochemical marker during treatment. However, before such approach can be generally recommended the cut-off values of the biochemical markers should be validated in future clinical trials of bisphosphonate. Postmenopausal osteoporosis develops slowly over many years and mainly becomes a significant individual and socio-economic health problem 1-3 decades after the menopause. Prevention of postmenopausal osteoporosis by bisphosphonates is therefore likely to imply a treatment regimen of at least a decade, as presently recommended for HRT (Consensus Development Statement 1997). However, future cost-effectiveness studies should reveal when bisphosphonate treatment should ideally be initiated. Our studies showed that the bisphosphonates were effective over the range from general recommendation (recently postmenopausal women with normal bone mass) to a reservation for women at particular risk of osteoporosis (elderly women, thin women, or women with osteopenia). Presently available biochemical markers could be used for groupwise and individual monitoring and prediction of treatment response. Most presently available biochemical markers, however, have the drawback of a low specificity. Recent studies of CTX measured in serum are promising, and indicate that this new biochemical marker might have overcome these drawbacks due to a pronounced response to treatment and a low long-term biological variation (Christgau et al. 1998b, Rosen et al. 1998, and 2000).