I didn't smack her because she needed antibiotics! I smacked her as it was the only way I found I could get her to take them at all. It shocked her for a second, which was enough, what with all the other more usual medicine administering techniques, to get her to swallow.
That time we were in hosp (asthma attack fwiw, she needed inhalers, oral steroids, paracetamol), when it was time for her to have her meds, all the available nursing staff were rounded up for lessons in how to administer meds to a resistant child. They tried their damnedest to get them into her (we had 5 nurses at one point, trying restraint, blowing in her face, stern talking etc), none of it worked.
Incidentally she used to put up the same level of resistance for tooth brushing. She has a couple if cavities, because I didn't think it was worth the whole brute force/smack routine for that.
She's grown out of this behaviour, now takes medicine, brushes teeth, etc. as required.
FWIW, I repeat, I've never smacked my youngest, he's never needed it.