Safety information on QT-interval prolongation: comparison of European Union and United States drug labeling. 
Prolongation of the QT interval can predispose to fatal ventricular arrhythmias.  Differences in QT-labeling language can result in miscommunication and suboptimal risk mitigation.  We systematically compared the phraseology used to communicate on QT-prolonging properties of 144 drugs newly approved (1st January 2006 to 1st June 2012) in the European Union (EU) and the United States (US), of which 66 mentioned the term 'QT' (two EU only, 28 US only, 36 both).  The agreement between authorities about the message on QT prolongation (does not prolong, unclear, possibly prolongs, prolongs) was moderate (kappa 0.434).  However, the agreement in expected clinical decisions based on the product labels was much higher (kappa 0.673).  The US drug label tends to be more explicit, especially when it considers absence of QT effects.