First thought is why would you need to do so. I had a cracked filling and an abcess and needed them before it could be fixed.
But then whilst Anti biotics are a pretty standard medication these days but the complaint return whilst you were away then they could reject any claim you put in, If worried then give them a call.

fwh

Usually you can find out what things you dont need to tell them about so it will probably depend on what the antibiotics are for, check through any paperwork or online.
A couple of years ago i was waiting for my gall bladder removed and luckily i had told my insurers as i had a problem with it on holiday, wouldve cost me a lot more than what it did if i hadnt let them know