Alendronate. A review of its pharmacological properties and therapeutic efficacy in postmenopausal osteoporosis.

Alendronate is an aminobisphosphonate which appears to attenuate, rather than completely inhibiting bone turnover, by suppressing the activity of osteoclasts. Clinical trials have established that 10 mg/day orally administered alendronate is the optimum dosage. Despite its poor bioavailability after oral administration, alendronate is highly effective at preventing bone loss associated with the absence of endogenous estrogen. A sustained increase in bone mass was observed during alendronate therapy without accelerated loss after withdrawal of the drug. Increased bone mass was associated with a reduction in the risk and rate of occurrence of vertebral fractures. A recent study demonstrated a 47% reduction in the risk of developing new radiographic vertebral fractures over 3 years in women with low bone mass and pre-existing vertebral fractures. There have been few direct comparisons in clinical trials. However, when compared with calcium or low dosages of salmon calcitonin (salcatonin) therapy in women with postmenopausal osteoporosis, alendronate induced a sustained increase in bone mass during therapy that was not seen with the comparator. In clinical trials alendronate was generally well tolerated when taken as recommended. Adverse events tended to be transient and usually associated with the upper gastrointestinal tract; the most common events included abdominal pain, nausea, dyspepsia, constipation and diarrhoea, which are also common with other bisphosphonates. Of potential concern are the small number of reports of patients developing oesophageal ulceration; however, this adverse event was attributed to noncompliance with the manufacturer's recommendations for administration of the drug. In addition, alendronate has not been associated with osteomalacia. Studies are still required to establish the long term efficacy of alendronate, particularly with regard to other available therapies. Although estrogen replacement therapy is generally considered the treatment of choice for the management of postmenopausal osteoporosis, many women are unable or unwilling to receive estrogens on a long term basis. Thus, alendronate, with its demonstrated beneficial effects and its good tolerability profile (when taken as recommended), is a promising alternative treatment option for the management of postmenopausal osteoporosis.