In the past years, osteoporosis was recognized as one of the complications of limb immobilization. It is the result of an imbalance between bone resorption and bone formation. This study assessments the effect of tamoxifen citrate on experimental osteoporosis in dog by histopathologic and radiographic methods. It has recently been suggested that antiestrogenic drugs could possibly be used as therapeutic agents in human. Tamoxifen has been used to treat patients with advanced breast cancer. Women who take tamoxifen may derive many of the beneficial of this drug such as a lowering of blood cholesterol and a slowing of bone loss.

The effect of tamoxifen citrate on bone mass in immobilization osteoporosis was studied in 14 adult dogs. Immobilization osteoporosis was induced by casting of the right hind limb for 45 days, while the left hind limb served as a non immobilization control. 7 dogs received tamoxifen citrate (1.5 mg/total body weight), once daily for 45 days. 7 dogs received no treatment. All dogs were euthanized on day 45 and bone samples were collected for histopathologic evaluation, the proximal ends of tibia were selected and fixed in 10% buffered formalin. Then the specimens transferred to 5% nitric acid solution. After decalcification, bone embedded in paraffin and sectioned at 5 micron and stained with hematoxilin and eosin Routine lateral and anteroposterior radiographs were taken of all tibia sampled for the morphometric comparison.

The results of this study indicated significant changes between controls and treatment groups. Histopathologic examination revealed that casting resulted in central and peripheral bone resorption which was characteristic of osteoporotic bone. Radiographic results showed that generalized bone lysis was occurred in immobilized tibia, but no sign of bone abnormality was seen in experiment group. Cortical thickness, medullary density and bone trabecular pattern were the same in both unrestricted limbs and immobilized cases which received tamoxifen citrate.

Histopathologic and radiographic results showed that tamoxifen citrate can prevent osteoporosis. Tamoxifen as a selective estrogen receptor modulator can increase bone density and may, therefore, reduce the incidence of osteoporosis. It acts like estrogen in some tissues (bone, liver, and uterus) and like an antiestrogen in other tissues (the breast). It seems that tamoxifen citrate inhibits PTH - induced bone resorption.