The NHS could save £84m a year by using a cheaper drug to treat a leading cause of blindness, research suggests.
NHS-funded research says both Lucentis and Avastin have a similar effect in preventing loss of sight when used for wet age-related macular degeneration.
Lucentis costs about £700 an injection, and Avastin £60 - but Avastin is not officially approved for eye conditions.
Novartis, which markets Lucentis in the UK, is taking legal action against four NHS trusts for using the cheaper drug.
The company says the use of Avastin - developed to treat cancer - is undermining patient safety.
Wet age-related macular degeneration, usually called wet AMD, is a common cause of loss of vision in elderly people - each year, at least 23,000 older people are diagnosed with the condition.
Lucentis is officially approved for use in eyes, and is the treatment recommended in England and Wales by the watchdog NICE.
Roche, which owns the rights to the similar, but cheaper, Avastin, has never sought to have it approved for use in eyes, which would involve further clinical trials.
But many doctors have been using Avastin at their clinical discretion.
Patients are usually treated with a monthly injection for the rest of their lives, whichever drug is used.
Both drugs restrict the growth of blood vessels, and were originally developed by the same company. Avastin was for use in cancer, Lucentis in treating wet AMD.
There has been no industry-funded clinical trial to compare the effectiveness and safety of Lucentis directly with the cheaper Avastin.
But publicly funded research is under way in both the UK and the United States to provide this head-to-head comparison.
The NHS-funded trial, called the IVAN trial, has involved 610 patients in 23 hospitals. It is one of the largest research projects studying eye disease in the UK.
The one-year results are being presented at an international conference on Sunday and have been accepted for publication in the peer-reviewed journal Ophthalmology.
Prof Usha Chakravarthy, of Queen's University in Belfast, led the clinical trial.
She told the BBC these initial results showed both drugs were effective in stopping the deterioration of sight, as measured by asking patients to read a standard eye chart.
"Regardless of which drug they received, the average person improved by approximately one line," she said.
"And when it comes to comparing the two drugs, the difference was extremely small - less than two letters on the eye chart."
'Serious safety concerns'
The greatest debate over the differences between the two drugs is likely to be over safety when used to treat wet AMD. Academics say overall, both drugs are extremely safe.
As they both target blood vessels, the IVAN researchers particularly looked at whether there was an increased risk of heart attack or stroke.
Professor Chakravarthy said the IVAN team was surprised to see a very slight increase in risk from Lucentis, but when the data was combined with the US research it became insignificant.
"Both drugs were equally safe, and the small differences that were found in terms of heart attack and strokes were cancelled out when we looked both at our study and the American study.
"In terms of other adverse events which put patients in hospital - these differences were consistent in both studies and we did observe a slight increase with Avastin."
Novartis argues that Lucentis has a safety profile proven in clinical trials and approved by the regulators.
It says the US research, which has just published data from the second year, highlights what it describes as "serious safety concerns" about the use of Avastin in this unlicensed treatment of eyes.
It points, for example, to a higher rate of stomach and gut disorders in patients given Avastin.
Tim Wright, the global head of development for Novartis pharma, said: "This underscores the importance of drug design and development with the patient and disease process in mind."
Financial stakes high
Cost pressures on the NHS have led to an increased use of Avastin.
The IVAN researchers estimate that if the NHS across the UK were to use the cheaper drug, it would save £84.5m every single year. That is based on an estimated 17,295 eyes being treated.
The Macular Disease Society welcomed the findings of the trials as "welcome contributions to our knowledge of the relative effectiveness" of the two drugs, saying: "It is interesting to see that they come to similar conclusions; both drugs work".
However, it added: "The trials cannot provide definitive safety information and the overall question of the safety of Avastin is, unfortunately, not answered to everyone's satisfaction by these trials.
"The use of Avastin will remain a matter of judgement for clinicians, with some satisfied with the evidence and others not."
It reiterated its call for the government for an independent appraisal of Avastin for use in ophthalmology.
Novartis is seeking a judicial review of the policy by four primary care trusts in England to pay for both Avastin and Lucentis.
The detailed grounds of the legal challenge have not yet been lodged with the court. The financial stakes are high both for the NHS and the pharmaceutical company.
Source: BBC News