Metoprolol tartrate is an immediate-release tablet that must be taken a few times a day. Metoprolol succinate, however, is a timed-release tablet that can be taken once a day. Metoprolol tartrate can be administered in the early stages of a heart attack to improve your outcome, but metoprolol succinate cannot be used in these situations.Metoprolol tartrate is also available as an injection for emergency situations. The two versions of the drug are not interchangeable as they have their own dosages and use cases.