An 89-year-old man died after being wrongly injected with undiluted potassium chloride at Sha Tin Hospital in June - the second blunder involving the same chemical to come to light in a week.
A week ago, a baby boy at Princess Margaret Hospital was injected with 0.3 milligrams of concentrated potassium chloride which had been prepared for another patient in the same ward.
He survived after emergency resuscitation.
Patients' rights activists were outraged yesterday and demanded a regular reporting system on all medical blunders.
Yung Wai-mui from the Patients' Rights Association said: 'It's ridiculous to see two such similar blunders in a week.
'The Hospital Authority should set up a reporting mechanism to report all the blunders quarterly - with the nature of the mistakes and measures taken for improvement clearly stated.' The latest blunders came despite new rules to prevent accidental overdoses handed down by the Hospital Authority last month.
But Ms Yung said the man's family stood little chance of substantial compensation because of his age.