Thousands of patients of Kaiser Permanente Health Plan in US may have received the wrong medications because of a glitch in the company's computer system.
The company said its computer systems had suffered a power outage that could have caused labelling errors on prescriptions dispensed to 4,700 patients on the 13 March.
Patients could have received incorrect prescription numbers, incorrect instructions about how to take the drug or even the wrong drugs.
Kaiser Permanente spokeswoman Kathleen Barco said the company is doing diagnostic testing on the system to determine exactly what happened and should have more information by the end of the week.
"This was a fluke occurrence," she said. "There was a power dip while we were testing our backup systems, and everything was shut down. When we came back online, an alert technician discovered that something had happened to the labelling system."
Barco said Kaiser Permanente has contacted at least 97% of the 4,700 affected patients via automated telephone calls, courier-delivered letters and, in some cases, home visits.
The company said there have been no adverse patient reactions to date.