A physician performing a procedure ordered heparin, 2,000 units, for the patient. The nurse went to the automated dispensing cabinet and retrieved two vials from a drawer that was supposed to contain heparin, 1,000 units/ml. However, look-alike vials of heparin, 10,000 units/ml, had mistakenly been placed there, and the patient received heparin, 20,000 units. When the nurse noticed the error, the patient received the heparin antagonist protamine and wasn't harmed.

A pharmacist should double-check all medications before they're placed in unit stock. And regardless of how many times you've removed a medication from its familiar location, always stop to read the label before you administer it.