In vitro activity and pharmacodynamics of oral beta-lactam antibiotics against Streptococcus pneumoniae from southeast Missouri.
OBJECTIVE
To determine the frequency of reduced susceptibility to penicillin, and to compare the in vitro activity and pharmacodynamics of oral beta-lactam antibiotics against clinical isolates of Streptococcus pneumoniae from southeast Missouri.


METHODS
Cape Girardeau, Missouri (population 35,500). Interventions. Minimum inhibitory concentrations (MICs) were determined for penicillin, amoxicillin, amoxicillin-clavulanic acid, cefprozil, cefuroxime, cefpodoxime, cefaclor, and loracarbef by E test for 108 isolates of S. pneumoniae. The MIC50, MIC90, and percentage susceptibility were calculated for each agent. Pharmacokinetic variables were obtained from the literature, and serum concentration-time profiles were simulated for a 25-kg child taking pediatric dosages commonly administered to treat otitis media. The average time above MIC (T > MIC) was calculated as percentage of the dosing interval using free concentrations and the MIC for each individual isolate. Analysis of variance (Scheffe post hoc test) was used to determine differences among agents for in vitro activity and T > MIC (level of significance, p<0.05).


RESULTS
The frequency of penicillin-nonsusceptible S. pneumoniae was 28.7% (31/108). For 25 penicillin-intermediate isolates, amoxicillin and amoxicillin-clavulanic acid were significantly more active than cefprozil, cefaclor, and loracarbef. The T > MIC for amoxicillin and amoxicillin-clavulanic acid, simulated at 13.3 mg/kg every 8 hours, was significantly longer than that for all other beta-lactams.


CONCLUSIONS
Amoxicillin and amoxicillin-clavulanic acid have superior in vitro activity and longer T > MIC for penicillin-intermediate isolates than the other oral beta-lactams.
Kays
M B
MB
Department of Pharmacy Practice, School of Pharmacy and Pharmacal Sciences, Purdue University, Indianapolis, Indiana 46202-2879, USA.
Wood
K K
KK
Miles
D O
DO
D000284:Administration, Oral; D000658:Amoxicillin / Q000494:pharmacology; D019980:Amoxicillin-Potassium Clavulanate Combination / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D008923:Missouri; D010403:Penicillin Resistance; D013296:Streptococcus pneumoniae / Q000187:drug effects*
D000900:Anti-Bacterial Agents; D019980:Amoxicillin-Potassium Clavulanate Combination; D000658:Amoxicillin