The causes of penicillin failure in eradicating Group A beta-hemolytic streptococcal pharyngo-tonsillitis (GABHS PT) are described. These include the presence of beta-lactamase producing bacteria that "protect" Group A beta-hemolytic streptococci (GABHS) from penicillins; the absence of bacteria that interfere with the growth of GABHS; co-aggregation between GABHS and Moraxella catarrhalis; and the poor penetration of penicillin into the tonsillar tissues and the tonsillo-pharyngeal cells. The use of antimicrobials that can overcome and modulate these phenomena and achieve better cure of the infection is described.