how long does cat cystitis last for with taking antibiotics?

Only a vet would know that.

My cat improved in 24 hours. she had antibiotics and pain Meds.

Make sure you give her the whole dosage.

What fun trying to put something down a cats throat !! it took 2 of us fighting 3 times a day.

most likely it will move up to the cat's kidney's..and cause a kidney infection which will then lead to kidney failure.

cats, unlike humans, will not increase their water intake to flush out bacteria...they will be in chronic pain, and because they can't take painkillers that will cause them to start peeing outside the litter box, hoping that it won't hurt anymore...and it can also be more than a simple infection--they could be having stones which cause pain and blood in urine....

Cystitis has the same symptoms of urinary tract infections. Without a urinalysis you cannot tell what your cat has. Cystitis needs treatment too - often anti inflammatory drugs, and pain meds to prevent the constant "need to go". And real infections do not go away without antibiotics, they just get more serious the longer they are left go.