It turns out that (instead of dear Siegfried) the KAOS agent is a health club manager named Hercules, played by John Fiedler. Fiedler does have the only bottle of the antidote, and Smart is determined to get it. But he is determined to even the score with Hercules as well. He manages to pour some of the same poison into Hercules' heath juice before he drinks it. When Hercules learns that he too has drunk the poison (and more of it than Smart did) he and Smart both reach for the bottle of the antidote to drink the contents first. As you can guess, Max wins the odd final arm wrestling battle.
I take it that the writers named Fiedler's character "Mr. Hercules" not only because they planned to have a small man like Fiedler play the part, but as a joke at the then noted body builder and health club entrepreneur Charles Atlas. If so, I wonder how many people today would catch the connection there.