The boy lost consciousness immediately, recovering only after 20 minutes of emergency treatment. He was in stable condition last night.

But last month, authority chief pharmacist Lee Pak-wai handed down a review pointing out the risks of such accidental overdoses and proposing ways to prevent them.

New red warning labels that read 'Must be Diluted' were on supplies of potassium chloride at Princess Margaret last week, the spokesman said.

'The nurse did not follow the three-step procedure,' she said.

'We do all this to enhance their awareness. We dare not say we will eradicate all mistakes, but we hope through higher education and training our staff can improve their vigilance.' The review urges increased staff supervision and training, the addition of special coloured syringes for medicines requiring dilution, and storage of dangerous concentrated drugs in an emergency cupboard.

'We're planning to remove all undiluted potassium chloride from wards if we can buy pre-diluted solution from the manufacturer,' the spokesman said.

The risk assessment review was handed down one year after a Queen Mary Hospital houseman accidentally injected a patient with concentrated potassium chloride.

Patients' Rights Association spokesman Yung Wai-mui said the repetition of the mistake was 'unacceptable'.

'The suggestions made last year have not been followed by Princess Margaret. Why have they not learned from their mistakes?' Ms Yung asked.

'The question is whether the whole system has problems or whether frontline workers don't refer to guidelines. An independent report or investigation is needed.' The nurse involved in the Princess Margaret incident was 'very stressed' and on leave, the authority spokesman said. The hospital is preparing a report on the incident.