antibiotics and alcohol

Hey. So I got prescribed antibiotics flucloxacillin on Friday ( two days ago) for mastitis from my nipple piercing. I haven't started the antibiotics yet as it was my mothers birthday yesterday and I wanted a drink with everyone. I didn't get drunk yesterday but knew not to have the antibiotics whilst drinking. Would I beable to start the antibiotics today or will the alcohol in my system cancel them out still? Or how long will I have to wait to start them ? Please don't comment how I'm stupid for not taking them straight away.