The 1% neomycin (mixed with the hydrocortisone ointment) is found in Neosporin.
What this article suggests is our lips might not be able to absorb what is applied topically if the problem is deeper inside lip, which requires injections to reach it. Or this ingredient makes the solution more absorbable in the tissue. I also know there is less blood flow to lips than other parts of the body.
The article does not state how long the doctors kept in contact with the patients after their lips healed.
Today, lidocaine is used instead of procaine to numb pain of injections.