Metoprolol succinate. Molecular model of the drug Metoprolol succinate (C15.H25.N.O3)?2?C4.H6.O4). This selective beta1 receptor blocker is sold under the brand name Toprol XL. It is used to treat high blood pressure, chest pain due to poor blood flow to the heart, and a number of conditions involving an abnormally fast heart rate. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue) and oxygen (red).