Abstract: The present invention provides for therapies characterized in part by co-administration or combination of antibiotic agents with medicinal compositions comprising as the pro-antibiotic active ingredient either a compound represented by a formula [I] or a pharmaceutically acceptable composite thereof; [wherein X represents oxygen, sulfur, NH, or N-alkyl; R1 and R2 represent hydrogen, tetrazole, or alkyltetrazole, respectively (with the restriction that if R1 is not hydrogen, R2 must be, and vice versa); R3 represents e.g., benzyl, phenyl optionally substituted, biphenyl, napthyl, N-phenylcarboxamido, etc., R4 represents e.g. carboxylic acid, or its alkyl esters, or a bioisoteric equivalent thereof, etc.; R5 represents e.g. hydrogen, carboxylic acid, etc.] in particular, medicine which is useful as therapeutic and/or protective drugs for infectious and/or inflammatory diseases. Other relevant compounds are also provided.