Abstract: Aim The postant ibio tic effects (PAEs) induced by Tienam (TIN), Carberin(CBN), Piperacillin (PIP), Mezloci llin (MZL), Cefope razone(CPZ)and Cefodizime (CDZM)against Escherichia coli and Pseudomonas aerug inosa were investigated.Methods PAEs were determined by spect rophotome tric method.Results PAEs induced by MZL, PIP, CPZ and CDZM against escherichia coli and Pseudomonas aerug inosa were rather short(<1h).No PAEs or negative PAEs were even found in the results of MZL against Esche richia coli.In genaral, β^-lactam antibiotics induced very short PAEs against Gram-negative bacilli.However, PAEs (1~3h)induced by TIN and CBN were markedly longer than those by the other four β^-latams.PAEs induced by CBN were significant longer than longer than that induced by TIN. PAEs induced by CBN and CBN were obviously concent ration-dependent.Conclusion The results suggested there were multiple mechanisms for PAEs induced by β^-lactams.The features of TIN and CBN should be emphasized when they are individually used to define drug dosing intervals in clinic.

Key words: PAEs, tienam, carbenin, piperacillin, mezlocillin, cefope razone, cefodizime, spectrophotometric method