If your farm is experianci g inordinate number of deaths that require constant but disperate intervention then the adage desparate situation require desparate messures may apply to you. It also may be likely you have made certain mistakes that cannot be easily reversed.
mistake number 1. Adding chicken from different sources to your flock (without quarantaine)
Mistake number two treating without disinfecting.
Mistake number three: probably too much antibiotic is messing liver and kidneys.
My prescription concentrate on prevention mire than cure. Bite the bullet and cull. Then start on a clean slate. Alternatively, relax and let natural culling happen. Down side of this the survivors maybe carriers even without showing symptoms.