Ceftin is a type of semi-synthetic antibiotic medicine which is chemically very similar to penicillin. It acts principally by slowing down or stopping the growth of bacteria. This is achieved by preventing them from forming the cell walls. Without this cell wall, the bacteria are unable to survive. This kind of antibiotic is able to act effectively against a wide variety of bacteria. It is however not effective against viruses. Doctors caution against overuse of any antibiotic as this tends to make it less effective.