A quick and convenient once-yearly treatment for osteoporosis is an exciting prospect for doctors and patients alike

Professor David Reid

In fact, the effect was similar to that produced by daily use of other drugs.

Like zoledronic acid these drugs belong to a class called the bisphosphonates - but they are taken in pill, rather than drip form.

Professor David Reid, an expert in rheumatology from Aberdeen University, said: "A quick and convenient once-yearly treatment for osteoporosis is an exciting prospect for doctors and patients alike.

"Oral bisphosphonates are effective in treating osteoporosis, but must be taken daily or weekly, are known to cause gastrointestinal side effects and are often associated with compliance problems."

Weakened bones

Osteoporosis is a condition in which the normal honeycomb structure of the bone is progressively weakened, leaving it fragile and vulnerable to fractures, most commonly of the wrist, spine and hip.

In the UK, one of three women over 50 suffer from this condition, which costs the NHS and government over �1.7bn each year.

Researchers tested zolendronic acid on 351 women at 25 centres in 19 countries.

They found that the treatment was effective, safe and well-tolerated.

Trevor Reid, of the National Osteoporosis Society, said: "Over three million people in the UK suffer from osteoporosis, and this figure is set to rise as more people live longer.

"Treating osteoporosis with a once-yearly infusion is an interesting concept which needs further investigation."

Zoledronic acid is manufactured by the pharmaceutical firm Novartis.

The research is published in the New England Journal of Medicine.