Running some numbers in the latest rules, and it seems that unless you have Medic-2 or better, you can't heal someone whose END has dropped to zero. Which is going to be the usual case, given how damage works. (Unless you get lucky with first aid, of course.)
They're better off natural healing until they can get at least 1 point back.
Might I suggest instead that either Medical Care becomes "3 + END DM + Medical Skill"?
Rationale: The natural "1D + END" healing rate allows you "crash" (as it should) if you're unlucky. Medical Care should be more predictable than that. '3' is an average D6 roll, and raising the constant from '2' to '3' means that not only can a Medic-0 keep a patient stable until a better doctor can be found, but an experienced Medic (Skill 1+) can actually help you recover.
Likewise, if Slow Drug is meant to be 30 days of Medical Care all at once, then a Medic-0 would be ill-advised to use it on an END-0 character, and an unskilled character would certainly kill the patient. (Again, as it should be.)
I suppose the question comes down to this: Is Medic-1 the entry level to being a proper medic, or is it Medic-2? I think we can all agree that Medic-0 shouldn't be good enough for much beyond first aid and emergency measures - useful to a party in trouble, but not really a proper healthcare professional.
And I presume (based off of the healing rate and maximum damage you can sustain on 2 characteristics) Slow Drug is meant to be a "heal up completely in one day" drug when administered by a competent medic, right?