Answer:
You should take him to the vet for that one. Found this off another question:
If they are not allergic (some are) yes but only some kinds will be effective in cats, for example amoxicillin (amoxi-tabs). The dosage depends on the illness and the weight. Usually is 5-10mg/lb once a day for 5-7 days
Don't ever give medication to an animal without consulting a veterinarian. For particular diseases, particular antibiotics should or should not be given. The wrong antibiotic in the wrong dosage can be very harmful to an animal and may contribute to antibiotic resistance in bacteria, which then can become more dangerous.