According to VetInfo, there are two main types of animal antibiotics that are safe for cats: bacteriostatic antibiotics and fungistatic antibiotics. There are also three human antibiotics that are safe for cats: amoxicillin, ampicillin and tetracycline.
The two antibiotics mostly prescribed for cats are the bacteriostatic antibiotics, which are used to fight bacterial infections, and the fungistatic antibiotics, which are used to fight fungal infections, explains VetInfo. A few human antibiotics can be used on cats, but vets don't often use them because it's difficult to gauge the proper amount and far too easy to overdose. Amoxicillin, ampicillin and tetracycline are all used to fight bacterial infections, although the milligrams per pound of body weight and the frequency vary for each one.
WebMD points out that using antibiotics on cats can produce problems. For instance, if used too often, a cat might develop an allergy to a certain antibiotics. Another issue is that antibiotics kill both good and bad bacteria, which can negatively impact the digestion of the cat and cause diarrhea. It is especially unsafe to give antibiotics to kittens or pregnant cats as the antibiotics can harm the kittens even before birth. Also, antibiotics are not always effective when fighting an infection, especially if the wrong antibiotic is administered or a strain of bacteria is particularly resistant.