Sorry to hear Biscuits is having bladder issues. No fun for anyone! Can I get a little more information? When is the last time he was seen by your vet for this problem? What, exactly, is Biscuits doing right now--straining, urinating outside the box, having bloody urine? The last time he was in, what did your vet see in the urinalysis?
Is Biscuits on a special diet at all?
The short answer to your question is that unless Biscuits had a cystitis episode not too long ago that your vet treated, it is unlikely that your vet will just prescribe antibiotics now, without seeing him. There are many things that can be going on, even if it looks like what happened in the past. Biscuits is at the age where bladder stones and crystals in the urine can be seen and that isn't necessarily just treated with antibiotics. Sometimes a prescription diet food can make a HUGE difference in the cat's clinical signs and, when fed long term, can almost eliminate bladder problems in the future. Sometimes cystitis is due to stress and isn't an infection at all. In that case, the cat's symptoms can come and go, so it can look like the antibiotics are helping, but they really aren't doing anything.
I guess that was the long answer, too! If this is a recurring problem for Biscuits, then it would be in his best interest to get to the root cause of his problems, try the diet change, and make sure he doesn't have any bladder stones or behavior "quirks" that need to be addressed.