Cephalexin (Cefalexin) is an antibiotic of the "first generation"
Cephalosporin group (a cephem). Like penicillin, it contains a beta-lactam "ring". Attached to this is a D-phenylglycyl group as substituent at the 7-amino position and an unsubstituted methyl group at the 3-position. Incidentally the phenylglycyl group is the same side-chain as ampicillin, which probably explains similarities in adverse reactions in some patients.
It is used to treat infections by organisms such as Proteus mirabilis
, Esherichia coli
, Klebsiella pneumoniae
, but not MRSA.
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