So sorry to hear about troubles... I completely understand as I've an 18# ex-gypsy now neutered male Main Coon. He now reacts better than four years ago when he sauntered into my apt quite ill and full-male. Wandered around for approx. 3 years. vet opines. Prob. lost or dumped. Very agressive or should say fearful.
If all normal has been tried, IF you can either afford it or cry at the vet.s. he/she could, might give logng-lasting shot and have you return every 3 or so days for another. Solves many probems. You could also learn to give shots yourself! Yes, you can. Learnwith orange. Get needles smallest TB needle size 1ml. But _not_ in loose hair on neck. New info from vets is that area for usual shots can casue those cancerous "bumps" on neck which we've all seen and felt.
You'll give shot in flank. Loose skin on back of rear leg. Hard I know, but less easy for him/her to bite you. Need strong animal-owner friend who is not afraid to help out. Wrap largish towel around said feline but keep one rear leg available.
Before everything, you have alcohol, needle, kleenex and paper towel to put this all on. Probably use kitchen table or area by sink. Can put non-skid Contac rubber mat liner under cat so it won't slide away from under you.
You first open antibiotic shot bottle lid (usually metal which flips off. kinda) and wiped top of that bottle with alcohol on say a piece of toilet paper, sterile cotton ball etc.. then take top off needle - tine usually fall into 2 pieces, top w/cap and needle and bottom part which hold medicine. - lay bottom on paper towel. fight with clean fingernails to carefully remove tight (very) needle cap from needle. Put cap aside. Place needle on bottom part. Push it on hard - very. Keep hands needle and Rx bottle top all extremely clean with the alcohol as you go. Can wash hands first or wipe them off with Purell-type alcohol hand cleaner.
Take needle and insert need top into medicine bottle's rubber top already clean ed with alcohol, remember? Pull bottom part's pluger very slowly to fill proper amount of Rx into needle. Slowly, as you'll see tiny bubbles in base of needle Fill needle base to a bit more than you will need for shot. The when needle still in bottle, push plunger at bottom slowly upwards after clicking finger on base of needle so all bubbles go to top. Then push the air bubbles out back into Rx bottle.
Hold needle to eye-level and remove needle from bottle then hold said needle over sink, and push out more air and some med into sink - keep careful eye on this as you want to get medicine at correct level in base of needle - say .5 ml. or whatever the Dr. said or wrote out on bottle.
Now stroke hind leg of kitty with hqnd and then alcohol fill cotton puff or piece of t.p. of some small piece of kellenx all of which you had already prepared by filing with the alcohol from that big alcohol bottle. You will rub skin where you wnat to give shot. Cat will kick - alcohol is cold. Be firm! Be sure needle with meds. is also firmly in otherh and. Be sure be tight and you will do it quickly. Got it?
Friend has cuddled kitty more firmly in towel wrap as you go and rubbed said feline's head and ears and talked it into a lull. EVERYONE IS CALM! Even soft music helpful. Small loving noises from "Mom/Dad Cat" is good, too.
Now pay attention.
Rememjbewr, the longer you take to give the shot, the more the cat will squirm and your friend will panic, etc. Bad scene. That's why I've given so many details. You will get ALL the medicine into the skin and probably even part in the muscle. Good! You get flu shots don't you? Well fast and clean is best.
Do the best for you cat.
Practice on oranges, apples, over and over with one or 2 needles until it is _automatic_. Do not let kitty think for even one moment this is your first try. You are head cat in the family and you are caring for your kit. Take that feeling deeply into your head and heart and hands. Firm loving care.
It will work and shots are a lot better than pink sugary kids' medicine all over the cat's fur, you, everywhere.
Practice, practice. Love your cat up. Walk away. All of this days before you begin. When you leave you cat wanting more rubs or yums... he/she will follow you for more. Just be casual. You are in control. Practice that, too.
Let this be a reminder to me, also. 18# and a good friend and an excellent vet all taught me this.
Best of luck and head catness to you all.
-Karen (& 3 Cat Crew)
P.S. Forgive misspellings and all. Poor eyes. etc. these days.