The reason that I don't know - is because the oral route works so quickly and thoroughly.
Lets suppose you are dealing with a patient with a very low bowel tolerance for ascorbate. In that case, you could administer the vitamin C safely IM/Intravenous, but provide the other "ingredients" orally.
B12 always makes sense.
All other safe IV except for possibly lysine and proline, unknowns, which aren't generally given IV to my knowledge.
Owen R. Fonorow, Orthopath (Orthomolecular Naturopath)
Love thru suffering