Cephalosporins

The cephalosporin ring structure is derived from 7-aminocephalosporanic acid (7-ACA) while the penicillins are derived from 6-aminopenicillanic acid (6-APA). Both structures contain the basic beta-lactam ring but the cephalosporin structure allows for more gram negative activity than the penicillins and aminocillins. Substitution at the "R" sites (different side chains) allows for variation in the spectrum of activity and duration of action.

Cephalosporins are grouped into "generations" by their antimicrobial properties. The first cephalosporins were designated first generation while later, more extended spectrum cephalosporins were classified as second generation cephalosporins. Currently, three generations of cephalosporins are recognized and a fourth has been proposed. Significantly, each newer generation of cephalosporins has greater gram negative antimicrobial properties than the preceding generation. Conversely, the "older" generations of cephalosporins have greater gram positive (staphylococcus and streptococcus) coverage than the "newer" generations.

A few generalizations can be made concerning the cephalosporins:

1. Gram positive coverage diminishes as gram negative coverage improves with each successive generation of cephalosporins
2. Total daily dosage of individual cephalosporins is similar within each generation
3. Frequency of dosing decreases with increasing generation(s)
4. Palatability improves (probably) with increasing generations
5. Most second and third generation cephalosporins havenít been approved for use in patients less than six months of age

Click here for more information on cephalosporin coverage. Click here for more information on the cephalosporin generations.

Send comments to Terry Leiker
Department of Nursing
College of Health and Life Sciences
Fort Hays State University
Revised October 2000