
I can tell you that one of mine once opened mail from hyperdrug and ate 6 x the wormer tablets (cestem the cheap drontal) he would normally have, he also ate a pack of zylkene. I phoned the vets in a panic and the vet said he might have an upset tummy but with all that zylkene on board he wouldn't care

He didn't even have an upset tummy and he's still fit and well years later, so I think yours will be fine

Talking of cheap wormers, I managed to get another years supply of milbemax from the NL, no prescription required at less than £2 a tab

They no longer deliver to the UK but I just got them delivered to a dutch friend who posted them on.