A nurse from Blackpool Teaching Hospitals Foundation Trust has been arrested on suspicion of administering poison to stroke patients.
Lancashire police said they were contacted by the trust after concerns were raised about the care of patients on the stroke unit at Blackpool Victoria Hospital.
They said a female healthcare professional – understood to be a nurse – was arrested in relation to allegations of mistreatment and neglect.
The Nursing and Midwifery Council has confirmed it has received a referral and is now “urgently” considering the case.
Lancashire Constabulary said they were contacted by the trust on 8 November after concerns were raised about the care provided to some patients on the stroke unit this month.
The female healthcare worker in question – who has been suspended by the trust - was arrested on suspicion of “administering any poison or noxious thing with the intent to injure and ill treatment or wilful neglect”.
She has been bailed until December 6.
Officers said they were at the very early stages of their investigation and enquiries were ongoing.
“This arrest is part of an on-going investigation into allegations of mistreatment of patients by a healthcare professional at Blackpool Victoria Hospital,” said detective chief inspector Jill Johnston.
“The inquiry is complicated and we have a team of specialist detectives working on this case who are also offering support to those families who have had loved ones identified as potentially being involved.”
She said the priority of both the police and trust was to ensure the safety of patients.
Trust chief executive Wendy Swift said the organisation was working closely with police.
“We can confirm a healthcare professional has been suspended in line with trust policy following allegations of mistreatment against patients on the stroke unit,” she said in a statement.
“We take all allegations of this type extremely seriously and when the concerns were raised we immediately contacted the police.
“The trust is working with the police and co-operating fully with their investigation.
“We would like to reassure all our patients that all necessary actions are being taken. The hospital remains a safe and caring environment for patients and the provision of services will continue as usual.”
The NMC confirmed to Nursing Times that it had received a referral in relation to the case.
“We can confirm that we have received a referral and we are urgently considering whether we need to take any sort of interim action,” said a spokesman.