Prescription drug makers will be required within two years to put bar codes on packaging in an effort to reduce potentially dangerous dispensing errors in hospitals, U.S. health officials said. The bar codes are meant to enable nurses and other healthcare workers to electronically verify that they are giving the right drug at the right dose at the right time. The Bush administration published a final regulation on the bar-coding requirement in February. Under the requirement, each bar code must contain a drug's unique identification number. Companies also may include information on the product's lot number and expiration date. A nurse using the system would scan a patient's identification bracelet and then the drug label, and then a computer would compare the information. An error message would appear if the drug, dose, or time of dose were incorrect.