One of the once yearly infusions for osteoporosis (decreased bone density -- brittle bones) is zolendronic acid - called Aclasta in some countries. Aclasta is not considered the first line therapy for osteoporosis since there are tablets that can be taken weekly from the same drug class (bisphosphonates) that are cheaper and safer to use. Of course anyone with osteoporosis should be taking calcium and vitamin D as well as getting plenty of weight-bearing exercise like walking. Before being treated with a drug like Aclasta, you need to be taking calcium and vitamin D and you need to do a blood test to check kidney function and to check levels of calcium and other salts in the blood. This is because one of the most common side effects of this drug is low blood calcium and this can give you bone and muscle pain and weakness. Less commonly it causes fever or leg swelling and very rarely can have the sever side effect of jaw bone necrosis (death).