Doxomax 800 mg Tablet SR is used to treat and prevent asthma and chronic obstructive pulmonary disease symptoms (a lung disorder in which flow of air to the lung is blocked). It works by relaxing the muscles in the air passageways, expanding them and making breathing easier. Doxomax 800 mg Tablet SR can be taken with or without food. Follow your doctor's instructions for dosage and duration. What you should take it for and how often you should take it depends on what you're taking it for. Take it for as long as your doctor recommends. If you forget to take a dose, take it as soon as you remember. It does not function instantly or prevent previously existing breathing problems, so keep your medical inhaler on hand in case of an emergency.