In vivo activity of amoxicillin and ampicillin against gram-positive bacteria: results of prophylactic studies.

In prophylactic treatment of intraperitoneal infections with Streptococcus pneumoniae (types 1 and 2) and Streptococcus pyogenes in mice, amoxicillin had a definite advantage over ampicillin in terms of protective effect. When the infecting agent was given to mice so as to produce an infection in the brain or lung (for example, S. pneumoniae given intracranially or intranasally), amoxicillin was also more effective prophylactically than ampicillin.