Analgesic used for pain associated with STEMI

Morphine is a very effective analgesic for the pain associated with STEMI.However, it may reduce sympathetically mediated aeriolar and venous constriction, and the resulting venous pooling may reduce cardiac output and aerial pressure. These hemodynamic disturbances usually respond promptly to elevation of the legs, but in some patients, volume expansion with intravenous saline is required. These side effects usually respond to atropine (0.5 mg intravenously). Morphine is routinely administered by repetitive (every 5 min) intravenous injection of small doses (2-4 mg), rather than by the subcutaneous administration of a larger quantity, because absorption may be unpredictable by the latter route.Ref: Harrison 19e pg: 1603