"It takes about 1 hour for medicine to reach the small intestine where it is absorbed so if there is less than 1 hour between giving medication and the second vomit, then IM or IV hydrocortisone should be given."

Now sadly one hour may not be fast enough in some circumstances.  IM injection is an instant thing.  I know because I once took Ash to the Doctors and he was blue in the face, and when he had the shot within minutes his face turned back to pink.  Seriously.  He had a vomiting illness and I always follow the above protocol.  Point is that was a vomiting illness and the decline is much slower.  In shock after an ijury, this can be so fast you really need to be able to give that shot yourself.  No delays.  The shot is there for such times.  Even if you don’t want to give it for illnesses, please get a kit for the "What if’s."