DESCRIPTION
Keflex® (Cephalexin Capsules, USP) is a semisynthetic cephalosporin antibiotic intended for oral administration. It is 7-(D-(alpha)-Amino-(alpha)-phenylacetamido)-3-methyl-3-cephem-4-carboxylic acid monohydrate. Cephalexin has the molecular formula C16H17N3O4S·H2O and the molecular weight is 365.41.
Cephalexin has the following structural formula:
The nucleus of cephalexin is related to that of other cephalosporin antibiotics. The compound is a zwitterion; i.e., the molecule contains both a basic and an acidic group. The isoelectric point of cephalexin in water is approximately 4.5 to 5.
The crystalline form of cephalexin which is available is a monohydrate. It is a white crystalline solid having a bitter taste. Solubility in water is low at room temperature; 1 or 2 mg/mL may be dissolved readily, but higher concentrations are obtained with increasing difficulty.
The cephalosporins differ from penicillins in the structure of the bicyclic ring system. Cephalexin has a D -phenylglycyl group as substituent at the 7-amino position and an unsubstituted methyl group at the 3-position.
Each Pulvule® contains cephalexin monohydrate equivalent to 250 mg (720 µmol) or 500 mg (1439 µmol) of cephalexin. The Pulvules also contain cellulose, D & C Yellow No. 10, F D & C Blue No. 1, F D & C Yellow No. 6, gelatin, magnesium stearate, silicone, titanium dioxide, and other inactive ingredients.
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