An annual intravenous osteoporosis treatment may stave off the bone-thinning disease that affects 10 million Americans, mostly women. In the late stages of osteoporosis, patients bones can break with normal movement, making it one of the more difficult nursing challenges in long-term care facilities. Researchers at the University of Auckland in New Zealand found that women who received intravenous infusions of a drug called zoledronic acid showed improved bone density for a year following the cessation of treatment. The study was reported in the Feb. 28, 2002, issue of the New England Journal of Medicine. Researchers concede that it will be about five years before doctors know whether the drug can prevent fractures. The drugs manufacturer has launched the needed longitudinal studies. The Food and Drug Administration has already approved zoledronic acid to treat cancer patients who develop a condition where calcium leaches out of the bones.