| 摘要 |
A cephem compound or pharmaceutically acceptable salt thereof represented by the formula I: <CHEM> wherein R1 and R2 may be the same or different and each represent hydrogen atom, nitro or cyano; R3 represents C1-C6 alkyl which may be substituted with carboxyl; R4 represents hydrogen atom or amino; X represents -S- or -SO-, there being no case where both of R1 and R2 are simultaneously hydrogen atom.
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