Enhanced effects of amoxycillin/clavulanic acid compared with amoxycillin and clavulanic acid alone on the susceptibility to immunodefenses of a penicillin-resistant strain of Streptococcus pneumoniae

The recent increase in the incidence of infections due to Streptococcus pne umoniae resistant to penicillin and other antibiotics, often associated wit h considerable morbidity and mortality has been recognized as an alarming p roblem. From the recent medical literature data it emerges that among beta- lactam antibiotics used as an empiric treatment for infections caused by S. pneumoniae, amoxycillin and amoxycillin/clavulanic acid are the most activ e oral antibiotics and may be considered as a first-line therapeutic agent for the treatment of these infections. Since the therapeutic result of the treatment of an infection is determined by the combined effect of the antim icrobials and host defenses, we investigated the effect of amoxycillin, wit h and without clavulanic acid, upon the in vitro interaction between human polymorphonuclear leukocytes (PMNs) and a penicillin-resistant strain of S, pneumoniae. Amoxycillin significantly inhibited the streptococcal uptake b y PMNs referred to the control system. Clavulanic acid did not have any sig nificant effect upon the interaction PMNs-S. pneumoniae. The addition of am oxycillin/clavulanic acid to phagocytes and streptococci resulted in a syne rgystic potentiation of the activity of both drugs upon the PMN functions t owards S. pneumoniae in such a manner that the bacteria became more suscept ible to either the phagocytosis or the microbicidal activities of phagocyte s. These effects came in addition to the intrinsic, excellent antimicrobial properties of this drug combination. Although the clinical significance of the observed enhanced effects of amoxycillin/clavulanate are far from eluc idated, the possibility exists that they may play a contributory role, espe cially in patients with impaired host defense.