To be fair to doctors, they don't have to prescribe you something just because you ask for it, and unfortunately there is probably no way to check if a letter from an IM is legitimate or not. Also some might not be familiar with the dosing of syntocin and vit K and while yes these can be looked up, the dosing and route of administration comes back to them and personally, I would feel uncomfortable prescribing a drug I was unfamiliar with just because someone I might not have met before came in with a letter from someone I do not know asking for it. If you need the prescription take the IM with you to explain the need. Just about all doctors I have worked with and dealt with personally can be reasonable if presented with a good rationale for why something is needed. I wouldn't be happy with a doctor who gave me antibiotics just cause I went in and asked for them I would expect to be examined and asked questions as to why I thought I needed them, and in a way this is no different.