Didronel PMO a combination of the drug etidronate and calcium is licensed specifically for the treatment of established vertebral osteoporosis, or serious bone thinning of the spine.
Last year, however, then manufacturer Norwich Eaton were so enthusiastic that they ran a campaign which appeared to urge doctors to prescribe it for wrist and hip fractures and also as a preventive for osteoporosis in women after the menopause despite the fact that the drug was not licensed for such use. The Consumers' Association responded angrily to such apparent poetic licence being taken, saying that the product was being "illegally promoted". (EA of their own accord, they say, withdrew the promotion.)
When taken continuously, studies show that etidronate can cause osteomalacia an adult form of rickets caused by lack of vitamin D. In 1976, researchers found that etidronate at a dose of 20mg per kilogram of body weight per day for six to 12 months did, indeed, reduce thinning of the bones. But it also caused a reduction in bone mineralization (RP Heaney and PD Saville, Clin Pharmacol Ther, 20;593-604). Didronel PMO is designed to be taken intermittently in conjunction with calcium carbonate supposedly to prevent osteomalacia. However, at least one study suggests that taken in this way, etidronate fails to prevent the loss of vertebral bone (R Pacifici et al, Miner Electrolyte Metab, 1988; 66;747-53).
Even if the drug does work, you may just be substituting one bone problem for another. An editorial in The Lancet warns that the length of time the drug stays in the body "could theoretically lead to increased amounts of 'old bone' in the very long term because of reduced remodelling." (5 May 1990) Etidronate's established side effects include angiooedema (water retension around the heart), nausea, diarrhoea, abdominal pain, constipation and vomiting. There have also been reports of patients developing aberrations in their white blood cells.