Hi XXXXXXXXXX,
It certainly is ok to give a cat penicillin, as long as they haven't had any adverse reactions to it in the past, and whatever you are trying to treat is susceptible to penicillin. We actually use it quite a bit in veterinary medicine.
Hope this helps. Any further questions, just reply and I will get back to you as soon as possible.
Sincerely,
Dr. CW
Veterinarian
9.5 years small animal clinical experience (7 in general practice, currently in shelter medicine)