This was discussed by Anthony Fauci on The Rachel Maddow Show last night. He said they're only effective if they are administered very early. The problem is that they require an IV setup and the research now is to render these drugs into more easily administered forms. The best and easiest would be a pill to take by mouth as soon as possible, but he said it looks like the companies are aiming at intramuscular or sub-cutaneous administration as a shot. But he kept going back to the early testing being needed to administer these treatments. They only have snippets of the program on the Maddow Blog, but you may find the bit I'm talking about. (Her regular program is available over cable or online services.)