document: The British Medical Journal claims it has revealed a campaign to derail research into the cancer drug Avastin.
  The claim has been denied by Novartis, the firm which markets the officially licensed drug, Lucentis, in the UK.
  Many doctors use Avastin as a cheaper but unlicensed alternative to treat wet age-related macular degeneration (AMD).
  AMD affects around 26,000 people each year in the UK and if left untreated can cause blindness.
  There is a licensed drug - Lucentis - which costs the NHS around £740 per dose.
  Trials have shown that another drug used to treat cancer - Avastin - is also an effective treatment, and is much cheaper, at between £50 and £65 per dose.
  Some doctors have been prescribing it, but it isn't licensed for this purpose.
  There is the added confusion of uncertainty over whether doctors could be personally liable if they prescribe an unlicensed drug.
  Both drugs are owned by the same company, Roche, but Lucentis is marketed by Novartis in the UK.
  The BMJ now claims it has evidence that clinicians with ties to Novartis urged some primary care trusts to pull out of one trial, and alleges the company tried to derail a second UK trial.
  BMJ editor-in-chief Dr Fiona Godlee said pharmaceutical companies should not be able to block access to alternative drugs.
  "Doctors' leaders also need to sort out the web of misinformation about drug prescribing that has been generated behind closed doors. and is costing the NHS hundreds of millions of pounds a year by scaring doctors from using cheap and effective medicines."
  A spokesman for Novartis denied the allegations.
  "We take any allegations seriously and are closely reviewing the content of the article.
  "Novartis is committed to improving health outcomes for patients with serious eye disease as demonstrated by our substantial engagement in ophthalmology, including significant research and development efforts in the UK.
  "Novartis continuously conducts clinical trials in the UK and other countries.
  "Discussions with UK study sites and healthcare professionals occur during all stages of these clinical trials.
  "During the feasibility stage these discussions often focus on the capacity and capability to conduct studies in accordance with the highest clinical and ethical standards."
  In November 2014, the Royal College of Ophthalmologists called for Avastin to be made available for treating the condition on the NHS, arguing that switching to the drug could save the NHS £100m.
  And in February clinical leaders from 120 clinical commissioning groups called on ministers and NHS England to clarify regulations that make it hard for physicians to prescribe Avastin for wet AMD.
  Do you have wet age-related macular degeneration (AMD)?You can share your experiences by emailing haveyoursay@bbc.co.uk.
  If you would be happy to speak further to a BBC journalist, please include a contact telephone number.
summary: A drugs firm has been accused of trying to block access to what some doctors believe is a cheap, safe and effective drug to treat a common eye condition.