Adrenaline is the drug of choice in acute hypersensitivity reactions (type1) -acute anaphylactic shock. This is because it relieves bronchospasm, angioneurotic oedema of larynx, prevents release of histamine from mast cells and maintains BP in anaphylactic shock.
Given intramuscularly(I.M): 0.3-0.5ml in 1:1000 solution.
In anaphylactic shock, the absorption of adrenaline through subcutaneous route is very poor. Hence, preferred route is I.M