A nurse killed two patients by deliberately administering fatal overdoses of drugs so he could feel the "thrill" of trying to revive them, a court heard yesterday.

Two people died and 16 were nearly killed by drug-induced respiratory problems while Benjamin Geen was a staff nurse at the accident and emergency unit of Horton general hospital in Banbury, Oxfordshire, the prosecution said.

Suspicions were aroused when nearly every patient who came near the 25-year-old nurse developed sudden breathing problems and deteriorated quickly and unexpectedly, prosecutor Michael Austin-Smith QC told jurors.

Mr Geen appeared before Oxford crown court yesterday charged with the murder of David Onley, 77, of Deddington, between January 20 and 23 2004, and Anthony Bateman, 67, of Banbury, on January 6 2004. He is also accused of causing grievous bodily harm with intent to harm 16 other patients, and 18 counts of administering a noxious thing so as to endanger life. He denies the charges.

Doctors at the hospital were initially bewildered by the rare and unexplained respiratory failures that took place between December 2003 and February 2004. But it then emerged that Mr Geen had been on duty in the A&E on each occasion, the court heard.

In the course of a nine-week period, he deliberately administered drugs or other substances to patients in order to make them collapse so he could enjoy the excitement of trying to revive them," Mr Austin-Smith told the jury.

"It's the prosecution's submission that this defendant loved these moments of drama. As he was later to tell police in interview, he hated the dullness of the minor side ... He preferred to be where the action is."

There had been "locker room chatter about the increased level of respiratory arrests", Mr Austin-Smith said, and suspicions came to a head when the 18th patient, Timothy Stubbs, went into unexpected respiratory arrest.

Mr Austin-Smith said Stephen Smith, who worked at Horton general, came to the "unpalatable conclusion" with his colleagues that a member of the A&E department had to be responsible.

An internal investigation was launched which found Mr Geen had been on duty on all 18 occasions when a patient suffered an arrest. Once the connection was made, Mr Geen was confronted at work and immediately suspended. He was arrested the same day and police found an empty syringe in his pocket. The pocket in which it was found was wet, and tests later established the liquid contained traces of drugs capable of causing respiratory failure.

Normal procedure was to throw out syringes after use, Mr Austin-Smith said. "You may wish to consider why the defendant was carrying around a syringe which had been used on a number of occasions," he told the jury. "When he realised he was going to be arrested he had plainly emptied that syringe."

The court heard that one of the men alleged to have been killed by Mr Geen was already very unwell when admitted in January 2004.

Anthony Bateman was asthmatic, arthritic, had a heart condition and was thought to have an underlying cancer. But this was not, experts later said, the reason for his respiratory arrest. Had doctors known that a muscle relaxant might have been the cause of the arrest, they would have resuscitated him. "This man was seriously ill and he may have died in any event but that is not the question for you," Mr Austin-Smith told the jury.

The second fatal case was also ill when he was admitted. But doctors said there was "no medical reason" why David Onley should have stopped breathing and lost consciousness - unless he had been given an unauthorised muscle relaxant. They said the respiratory arrest would have made Mr Onley more vulnerable to the heart attack he later had.

The trial continues.