Combined regimens on empirical basis have occasionally been employed because of the difficulty of the identification of causative organisms in respiratory infections. The combined regimen of penicillin and aminoglycoside has been proved useful from both bacteriological and clinical view points in cases of infections caused by P. aeruginosa, This report deals with the in vitro evaluation of the effectiveness of the combination of CBPC plus DKB or AMK against various species of or ganisms isolated from patients, and the clinical evaluation of the effectiveness of the combined regimen of CBPC and aminoglycoside in cases of extremely severe respiratory infections. Results of in vitro experiments: S. pneumoniae, S. pyogenes and alpha hemolyticus were sensitive to CBPC, and the combination of CBPC and DKB showed synergistic or additive effects. H. influenzae was sensitive to both CBPC and DKB, and the combination of the two durgs showed synergistic or additive effects. S. aureus was sensitive to DKB, and the combination of CBPC and DKB showed additive effects. P. aeruginosa and Serratia were sensitive to CBPC and DKB, and the combination of CBPC and DKB showed synergistic effects. E.coli, K. pneumoniae and E. cloacae were resistant to CBPC, and the antagonism between CBPC and DKB was observed on several strains. The combination of CBPC and AMK showed synergistic effects against most of the organisms studied. The MIC of DKB against S. aureus, P. aeruginosa or Serratia was lower than that of AMK and the combination of CBPC and DKB was more effective than that of CBPC and AMK. The MIC of AMK was lower than that of DKB against resistant strains of S. aureus or E.coli and the combination of CBPC and AMK was more effective than that of CBPC and DKB. Results of clinical application: in cases of severe respiratory infections, which could be treated only with difficulty, 10 to 20 mg of CBPC were administered (IV drip) in combination with aminoglycoside (IM). The causative organisms of the respiratory infections were eradicated in 11 of 19 cases (57.9%). The over-all therapeutic effects of the combined regimen of CBPC and aminoglycoside in respiratory infections were good in 11 of 19 cases (57.9%), fair in 2 of 19 cases (10.5%) and poor in 6 of 19 cases (31.6%).
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