If tonsillitis is caused by a bacterial infection, your doctor will prescribe a course of antibiotics. Penicillin taken by mouth for 10 days is the most common antibiotic treatment prescribed for tonsillitis caused by group A streptococcus. If your child is allergic to penicillin, your doctor will prescribe an alternative antibiotic.
https://www.mayoclinic.org/diseases-conditions/tonsillitis/diagnosis-treatment/drc-20378483

