Repeated abcess in the same foot?

My sister's tb came in out the field very lame, initially the vet thought it was something in his hip or stifle but thankfully it's turned out to be an abscess instead of something nasty. This is the second abscess he's had in the same foot within a couple of months. We' know what we're doing with treating it and our farrier came and opened up the abscess on the sole but because it took a couple of days to accurately diagnose the abscess it's also burst out at the coronet band. It's right at the front of his back hoof. He's getting it poulticed a couple of times a day and is on painkillers but I was wondering if there could be some residual infection from the first abscess (it was round to the side) and if antibiotics would be indicated? We are speaking the vet on monday about this as well as our farrier. He's barefoot and has never had shoes on (he's 5) and we have no intention of shoeing at all if possible.