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This drug is resistant with respect to a broad spectrum of beta-lactamases. Its spectrum of activity is analogous to that of the third-generation cephalosporin cefotaxime (32.1.2.56), although it is more active with respect to some staphylococci, enterococci, and also a few enterobacteria. Synonyms of this drug are cefrom, cedixen, and others.

32.1.3 Penems and carbapenems

Besides penicillins and cephalosporins, which are synthesized by mycelial fungi, substances also belonging to the beta-lactam antibiotic group include those that are produced by streptomycetes, which are called penems. This class of antibiotics is chemically similar to derivatives of penicillanic acid; however, it differs from the others in the presence of an endocyclic double bond conjugated with the carboxyl group, which gives them a certain familiarity with cephalosporanic acid; in the presence of a five-membered ring of the S-alkyl substituent instead of two methyl groups in the second position, and in the absence of an amino group in the sixth position. Penems SCH-29482 (r = CH2CH3) and -34343 (R = CH2CH2OCONH2) have not yet found use in medicine.

Carbapenems are representatives of another class of antibiotics that differ from penems in the absence of a sulfur atom in the penem ring. They include: thienamicin (R = CH2CH2NH2), olivanic acid (R = CH=CHNH2), and imipenem (R = CH2CH2NHC=NH).

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Imipenem: Imipenem, [5^-[5a,6a(^)]]-6-(1-hydroxyethyl)-3-[[2-[(iminomethyl)amino] ethyl]thio]-7-oxo-1-azabicyclo[3.2.0]hept-2-en-2-carboxylic acid (32.1.3.1), is the only car-bapenem presently used in clinics. It is synthesized from thienamycin isolated from Streptomyces cattleya by reacting it with the methyl formimidate [179-182].

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