IN-VITRO ACTIVITIES OF ORAL ANTIMICROBIAL AGENTS AGAINST PENICILLIN-RESISTANT STREPTOCOCCUS-PNEUMONIAE - IMPLICATIONS FOR OUTPATIENT TREATMENT

We tested 83 penicillin-intermediate (Pen(i)) and 50 penicillin-resist ant (Pen(r)) isolates of Streptococcus pneumoniae against eight oral a ntimicrobials. Clarithromycin's MICs (minimal inhibitory concentration ) were generally the same or one to two dilutions less than those of a zithromycin. Seventy-two percent of Pen(i) isolates were susceptible t o clarithromycin and azithromycin, in contrast to 42% and 40%, respect ively, of Pen(r) isolates. Cefuroxime activity exceeded that of cefpro zil, which exceeded that of cefaclor, in Pen(i) isolates. For all thre e cephalosporins, MICs of 90% of isolates tested were greater than or equal to 3 dilutions higher for Pen(r) isolates than for Pen(i) isolat es. Percentages of Fed isolates susceptible to clindamycin and tetracy cline were 92% and 83%, respectively, and 78% and 82% for Pen(r). Only 49% of Pen(i) isolates and 4% of Pen(r) isolates were susceptible to trimethoprim-sulfamethoxazole. Azithromycin, clarithromycin, cefuroxim e, cefprozil, clindamycin, and tetracycline may be useful in treating infections caused by Pen(i) S pneumoniae, but Pen(r) isolates are freq uently resistant to both old and newer agents.