A coroner is calling for action after a woman died when prescribed two medications which together "caused exceptional thinning of her blood".

Susan Gladstone, from Letchworth, had been prescribed warfarin for a number of years.

The 62-year-old was prescribed tramadol for low back pain, but three weeks later suffered a brain haemorrhage and died.

Mrs Gladstone's inquest concluded that "she died as a result of a generally unknown interaction between warfarin and tramadol which caused exceptional thinning of her blood."

Now, the assistant coroner for Hertfordshire, Graham Danbury, has written to NHS England advising that "during the course of the inquest, the evidence revealed matters giving rise to concern," and warning that "there is a risk that future deaths will occur unless action is taken."

In a Prevention of Future Deaths Report sent to NHS England, Mr Danbury writes: "There was nothing to warn the prescribing doctor of any possible interaction.

"In my opinion, action should be taken to prevent future deaths and I believe you, NHS England, have the power to take such action."

NHS England must respond to the report by February 6, with details of action taken or proposed to be taken, setting out the timetable for action. Otherwise, it must explain why no action is proposed.

Two days before she died, Mrs Gladstone was admitted into Lister Hospital in Stevenage "with a history of feeling increasingly unwell over the preceding few days," Mr Danbury explained.

He said her "level of blood thinning was detected," and  "immediate action to reverse this was taken."

However, Mrs Gladstone’s condition deteriorated and she died.

Theresa Murphy, chief nurse at the East and North Hertfordshire NHS Trust, which runs Lister Hospital, said: "We would like to offer our sincere condolences to Susan’s family following her sad death.

"We remained in contact with Susan’s family through the trust’s complaints process, and assisted the coroner with the inquest into the circumstances of her death.  

"Whilst the investigation identified some peripheral learning for the trust, it did not raise any concerns relating to the care Susan received.

"On being notified of the new medication that Susan had been given, a review was arranged with the anti-coagulant clinic. Sadly, before this review took place Susan became unwell, came into our care and sadly died.

"In his report, the coroner noted the interactions of the medications prescribed is not widely recognised and therefore issued the Prevention of Future Deaths notice to NHS England in order to raise awareness, and ensure that all organisations are aware of the potential interactions."