Thanks Sam, further reading I found this:
In addition, as regards renal excretion of the active
substance, animals with severe renal dysfunction should not be treated, in order to avoid potential
adverse effects that may be associated with accumulation of the substance.
What adverse effects? could that be why Suzie was howling from that Friday throughout the weekend, was there an accumulation of the stuff making her feel worse. I don't know why my vet gave her antibiotic anyway - I wasnt thinking straight - all I wanted was something to make her feel better and I've always trusted my vet, I didnt question what she was giving her and I can hardly bear this now, because I'm thinking that injection was just too much of an assault on her failing kidneys, and I my vet let it happen and I let it happen, I'm gutted and in tears, its brought it all back.