Four cases of incorrect administering of drugs occurred at Nihon University Itabashi Hospital in 2015 and 2016, including a case in which a patient's heart briefly stopped after being given the sedative Precedex at a rapid pace, sources said.

The hospital, based in Tokyo's Itabashi Ward, admitted the dosage errors Wednesday and issued a statement of apology, saying it was taking preventive measures. The hospital said it has stopped using the drug.

Instructions attached to Precedex packages warn of serious problems if it is not properly administered.