Clinical trial of fluoride in osteoporotic women: Extended observation and additional analyses

[New osteoformative agents for osteoporosis]

PURPOSE

Antiresorptive therapy are usual treatment of osteoporosis, but they prevent no more than 40 or 60% of osteoporotic fracture. Thus, there is a need for osteoformative agents that can further augment bone mass and reduce risk fracture more substantially. CURRENT KNOWLEDGER AND KEYPOINTS: Daily injections of 1-34 aminoterminal fragment of PTH increase bone formation and bone mass. A randomized study recently demonstrated that PTH 1-34 decrease the risk of vertebral and non vertebral fracture, and the place of this treatment in the strategy of osteoporosis treatment is to demonstrate. Oral administration of strontium salt at low dosage level stimulate bone formation and decrease bone resorption. Preliminary data needs to be confirmed by a multicenter antifracture study. Retrospective results with statins in three international studies have not be confirmed by the only randomized clinical trial. Use of low dose intermittent fluoride therapy are still recommended by some authors. FUTURES PROSPECTS AND PROJECTS: Effects of insuline like growth factor I and other growing factor on bone turnover have to be confirmed in human, and pharmacological and tolerance problems have to be solved.

In corticosteroid-treated respiratory diseases, monofluorophosphate increases lumbar bone density: a double-masked randomized study

The efficacy of a monofluorophosphate-calcium combination (MFP-Ca) in increasing lumbar bone mineral density (BMD) was assessed in a prospective double-masked study. Patients (n = 35), who had been treated for 1 year or more with prednisone-equivalent doses > or = 7 mg/day for asthma or other respiratory diseases, were randomly assigned to receive twice a day, for 2 years, either one MFP-Ca tablet [100 mg sodium monofluorophosphate (13.2 mg F-) + 500.5 mg Ca2+] or one Ca tablet (500.5 mg Ca2+). BMD was measured from L2 to L4 using a dual photon absorptiometer. The eligible patients (7 premenopausal women, 21 men), who had no previous vertebral fractures and were aged 46.5 (21-65) years, had received 18 (7.5-60) mg prednisone-equivalent/day and had a mean lumbar BMD of 0.917 +/- 0.141 g/cm2 at baseline (MO); in these 28 patients, the mean increase in lumbar BMD at final assessment was significantly greater in the MFP-Ca group (p = 0.05; Mann-Whitney). There was also a significant difference after 2 years between the two groups (p = 0.05, ANOVA) in favour of MFP-Ca, with an increase in lumbar BMD of 11% (MFP-Ca) compared with 1% (Ca); thus, with MFP-Ca, lumbar BMD increased by an average of approximately 5.5%/year. There was no statistically significant difference between the two groups in doses of corticosteroids used during the 2 study years, rate of vertebral fractures, or frequency of side-effects (which were all minor). No bone fissure was observed. Thus, the daily dose of 200 mg monofluorophosphate (26.4 mg F-) combined with 1 g Ca2+ in patients with long-term corticosteroid-treated respiratory diseases appears to be a safe and efficient way of increasing lumbar BMD, suggesting that its use should be further studied in corticosteroid-induced osteoporosis.

Fluoride and the skeleton

Fluoride has the potential to increase skeletal mass to a greater extent than any other pharmacologic agent, yet it has proven difficult to translate this into therapeutic benefit for patients with low bone mass in diseases such as osteoporosis. This apparent paradox can be explained in part by toxic actions of the ion on skeletal mineralization, impairment of the normal processes of bone resorption, and fluoride-induced decreases in strength per unit of bone (mass or volume). In part, the paradox can be explained by the late stage of osteoporosis in most patients enrolled in controlled clinical trials of fluoride, with alterations in skeletal microarchitecture beyond which restoration of mechanical integrity is not likely. Exposure of calcified tissues to environmental fluoride (water supply, dentifrices) also offers paradoxes. The anticaries effects are well documented as are the deleterious skeletal effects of endemic fluorosis when environmental exposure is too high. More controversial is the effect of seemingly nontoxic levels of exposure on the prevalence of osteoporotic fractures of the hip. This review attempts to provide a balanced overview of the conflicting literature concerning therapeutic and environmental effects of fluoride on the skeleton.

Fluoride therapy of type I osteoporosis

Sodium Fluoride (NaF) is the only medication so far clinically available with a bone formation stimulating property, through its peculiar mitogenic dose-dependent action on the osteoblast cell line. Bone strength is commensurate to bone mass, and in a condition with fragility fractures, like osteoporosis, it seems logical to restore bone mass without weakening bone strength. However, as with any active drug. NaF therapy requires adhesion to elementary rules if drawbacks are to be prevented. A first mandatory rule is not to prescribe NaF without calcium supplementation, if bone loss at the appendicular skeleton is to be avoided; to prevent this, the availability of monofluorophosphate (MFP), containing the fluoride and calcium salts in the same preparation has enhanced the compliance to calcium supplementation. A second rule is not to give supraphysiological doses of vitamin D, for the same reason. Third, if one wants to avoid a calcium shift from cortical to trabecular bone and osteomalacia, one should use small doses of NaF, of the order of 50 mg/day. With this in mind, the bioavailability of the drug has to be taken into account, particularly its gastrointestinal absorption which is dramatically enhanced if a plain non entericoated (EC) capsule is used, as compared to that of an EC tablet with the same face value. Too much NaF is deleterious to bone, a fact known for years. Already in 1972, it was noted that in all patients receiving 60 mg or more of NEC NaF, daily, morphologically abnormal bone developed and which appeared irregular and contained areas of incompletely mineralized bone. The bone was histologically and microradiographically normal in patients receiving 45 mg or less of NEC NaF/day. Fourth, NaF therapy is contraindicated in renal insufficiency owing to an enhanced retention in the skeleton. NaF is, however, by no means the ideal medication, because its therapeutic window is narrow. It has many bothersome drawbacks, and notably it is irritating for the gastric mucosa, a hazard which may be partly circumvented by the use of an Ec or slow release tablet. Furthermore, peripheral stress fractures may occur, and, in our experience, they were seen in 17% of patients, almost exclusively in females with a low lumbar BMD. Their occurrence should be curtailed by not allowing an increase in alkaline phosphatase activity of more than 50%. This is a relatively benign complication, because no stress fracture degenerated into a complete fracture. In all cases, the stress fractures healed after a transitory drug discontinuation. If there is some concern about cortical bone, NaF therapy may be associated with an antiresorber like estrogens which will prevent any further bone loss, and does not impair the response to NaF. NaF therapy should be reserved for patients suffering chiefly from trabecular osteoporosis and should be avoided in senile osteoporosis, because of a frequently impaired renal function. Currently, we would recommend in clinical practice a daily dose of 50 mg EC-NaF or 150 mg Ca-MFP as the therapy of involutional osteoporosis in women, reserving the dose of 75 mg EC-NAF or 200 mg MFP for males or female patients resistant to lower dose. The therapy should be maintained for 2 to 3 years, or more, according to the bone response, taking into account that patients with the vertebral crush fracture syndrome have lost on average 30%, as compard to the young adult mean.

Monofluorophosphate increases lumbar bone density in osteopenic patients: a double-masked randomized study

To assess the efficacy of combined sodium monofluorophosphate and calcium therapy (FC) in increasing lumbar bone mineral density (BMD) in patients with low bone mass, we conducted a prospective double-masked randomized study in 94 patients aged 50-70 years. Patients were selected on the basis of a lumbar BMD at least 2 standard deviations (SD) below the young adult mean (T-score) but without evidence of previous vertebral fracture (severe osteopenia). They were randomly assigned to receive for 2 years, twice a day, either FC (13.2 mg F-, i.e. 100 mg sodium monofluorophosphate, and 500 mg Ca2+) or C (500 mg Ca2+). Vertebral BMD was measured by dual photon absorptiometry from L2 to L4. Comparison at final assessment in the 76 eligible patients (Student's t-test) showed a statistically significant difference between the two groups in the mean BMD increase in favour of FC. Furthermore, Student's t-test showed a significantly greater increase in lumbar BMD in FC-treated patients at 1 year, at 18 months and after 2 years (mean increase of 7.1%/year). These results were confirmed by ANOVA at 1 year, at 18 months and after 2 years of treatment. Of the FC-treated patients, 71.4% were considered to have responded (i.e. they showed an increase in lumbar BMD of more than 0.034 g/cm2). The dosage of 26.4 mg fluoride ion/day (i.e. 200 mg monofluorophosphate/day) therefore appears to be safe and to increase the BMD effectively in patients with low bone mass prior to vertebral fracture.

Abnormal bone mineralization after fluoride treatment in osteoporosis: a small-angle x-ray-scattering study

Sodium fluoride treatment of osteoporosis is known to stimulate bone formation and to increase bone mass, but recent clinical trials failed to prove its antifracture effectiveness. The formation of bone with abnormal structure and, therefore, increased fragility is discussed as a possible explanation. Until now, however, exact information on the mineral structure of osteoporotic bone after fluoride treatment has been lacking. Bone biopsies were taken from three patients with postmenopausal osteoporosis before and after fluoride treatment (60 mg NaF/day for 1-2 years), from one patient with iatrogenic fluorosis, as well as from three normal controls. The mineral in these samples was investigated by a combination of backscattered electron imaging and small-angle x-ray scattering. Depending on the total dose of fluoride, an increasing amount of new bone is laid down on the surface of preexisting trabeculae. Its mineral structure is identical to that of heavy fluorosis and is characterized by the presence of additional large crystals, presumably located outside the collagen fibrils. These large crystals, which are not present in the controls or in osteoporotic bone before fluoride treatment, contribute to increase the mineral density without significantly improving the biomechanical properties of the bone. The possible success of fluoride treatment depends not only on the amount of newly formed bone but also on the rate of bone turnover. Indeed, as soon as significant amounts of fluoride are present, bone turnover leads to the replacement of old (normal) bone by new (pathologically mineralized) bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-dental tissue effects of fluoride

The anti-caries effects of water fluoridation are well-established. The non-dental tissue effects of fluoride in drinking water, either naturally occurring or as an additive, have been too poorly studied to permit definitive conclusions to be drawn. Claims have been made that fluoride results in an increased occurrence of malignancies, particularly osteogenic sarcoma. Experimental rat data have not resolved this issue, and epidemiologic studies are equally unclear. Initial claims that fluoride offers protection against atherosclerosis remain viable, but here too, much more directed research is needed. Early studies suggested that a water fluoride content greater than 1 ppm resulted in a lower prevalence of osteoporotic fractures. Recent epidemiologic data seriously question this conclusion and raise the possibility that even this relatively low level may increase the prevalence of osteoporotic hip fractures. Other elements, including calcium and magnesium, also vary in amount as water fluoride content varies, and it has proved difficult to distinguish the independent effects of the various nutrients in water from each other. Therapeutic use of fluoride has been largely restricted to studies of its effect on the osteoporotic study, this important issue remains unresolved. This review provides an overview of these issues, focusing on the uncertainties alluded to, and attempting to develop strategies for future research.

Treatment of symptomatic osteoporosis with fluoride

Fluoride has been used for > 30 years in the management of osteoporosis. It is one of the few agents that has marked anabolic effects on the skeleton. Indeed, treatment results in continued increments in cancellous bone volume so that cancellous bone volume can be restored to normal in patients with advanced osteoporosis. Despite its long history, both the efficacy and risks of fluoride regimens continue to be the subject of controversy. One of its problems is its age, and much of the early work undertaken utilized methodology and proofs that are today unacceptable. A further problem is that sodium fluoride as a treatment is cheap and not patented (although some formulations are), so that it has been difficult for investigators or industry to make the investments required to provide a modern program of evaluation.