Antibiotics are only prescribed for tonsilitis if the infection is bacterial rather than viral since they are ineffective at fighting viral infections. When tonsilitis is bacterial, it is most commonly caused by the bacterium known as Streptococcus pyogenes, also known as group A streptococcus. For group A streptococcus, the typical prescription is oral penicillin for ten days, unless your child is allergic to penicillin and requires a different antibiotic. When you bring your child to KidsHealth Pediatrics for tonsillitis treatment, their pediatrician will provide you with all of the necessary information and instructions regarding antibiotic treatment if a bacterial infection is what is causing the illness.