A widely used antibiotic long considered safe dramatically increases the risk of cardiac arrest, particularly when taken with some popular drugs for infections and high blood pressure, a huge study found.The drug is erythromycin, which has been on the market for 50 years and is prescribed for everything from strep throat to syphilis. The new study shows the need for continuing research on the safety of older medicines, including how they interact with newer drugs, said researcher Wayne A. Ray, a professor of preventive medicine at Vanderbilt University School of Medicine in Nashville.In patients taking erythromycin along with other drugs...