Ask the vet without whose advice you should not be dosing you kitty.
Some 1 in 2 to 3 thousand cats can develope what is called Shot Knot, especially when administered in the back of the neck, shoulder area. Many vets these days recomment shots in the loose fold of skin at the back of the rear legs, where shot knot, if occurring, could be surgically dealt with, unlike at the neck or shoulder, an inoperable region.
Shot knot often leads to cancer developement, according to articles i have read, and vet opinions i have experienced.
see it in wikipedia, and elsewhere on line
In the shoulder area, pull up the loose skin, then inject it there. I have had to give cats shots before and my veterinarian friend instructed me how to the first time.
Yep, it was penicillin. he was an outdoor cat and had been in a fight. he had a real nasty place above one eye that became infected. I asked the vet about the hindquarter shots. He said that he preferred penicillin to be between the shoulders. That was good enough for me.
usally in the bathroom