HOW a prescribed drug being taken by a 58-year-old woman, formerly a patient at Green Lane Hospital in Devizes, reached a fatal level was a mystery, an inquest heard.

Wiltshire coroner David Masters has called on National Health Service chiefs to launch a countrywide inquiry, he said at the hearing in Salisbury on Friday.

Mr Masters said Christine Keen's death may have been caused by the drug, an anti psychotic medication called Closopine, being taken in combination with other drugs.

The inquest, held on November 4 in Salisbury, heard Mrs Keen had been living at the Dunraven residential home for people with mental health problems in Salisbury and died after being rushed to hospital when she collapsed in July last year.

Mrs Keen had been at the home for five months after being transferred from Green Lane Hospital in Devizes.

Tests showed Mrs Keen had more than four times the top of the therapeutic range of the drug.

Eileen O'Connor-Marsh, proprietor of the Dunraven home, told the inquest medication was carefully monitored and administered to residents by well trained staff.

The coroner heard Mrs Keen showed no evidence of suicidal thoughts and the likelihood of her being able to secrete tablets was put at a "mild possibility."

Mr Masters said: "It seems to me there is a puzzle. Everyone is very surprised at the level but no-one has an explanation, unless there is some connection with the combination of drugs she was taking."

He asked the NHS's chief pharmacist to hold an investigation to discover whether there have been any similar cases.

He said he wanted to ascertain if there "was something akin to what has happened here."

He recorded a verdict of misadventure.