Cephalosporins

This group of antimicrobials, though similar to the penicillins in action, have different chemical structures. They tend to be more stable than penicillins to many of the bacterial beta-lactamases, and have a broader spectrum of activity than do the penicillins.

There are many cephalosporins that are different classes, and which vary in their spectrum of activity, but all of the so called “true” cephalosporins derive from cephalosporin C produced by Cephalosporium acremonium.

These drugs are usually bactericidal. They inhibit mucopeptide synthesis in bacterial cell walls.
Their advantage over the penicillins are that they resist hydrolysis by the enzyme penicillinase which is secreted by a number of bacteria.
The cephalosporins can be effective, but those that are taken orally are not in most cases the drug of choice in systemic infections.

There are three generations of cephalosporins. The “first generation” have spectrums of activity that are quite similar. They give coverage against many Gram-positive organism and anaerobes; but show poor activity towards Gram-negative organisms.

First generations drugs are, cephalothin, cefazolin, cephapirin, cepadrine, cephalexin, and cefadroxil.

The “second generation” of cephalosporins have expanded Gram-negative coverage besides having activity against Gram-positive further like the first generation.
Because there is considerable variation of activity among the drugs in the second generation, testing for susceptibility may be required to determine the drugs sensitivity to the organism it is planning to be used on.

Second generation drugs are, cefaclor, cefamandole, cefonid, ceforanide, cefuroxime (only second generation drug that crosses blood brain barrier), and the cephamycins cefotetin and cefoxitin.

In the “third generation”, these drugs are able to penetrate the central nervous system and have even greater activity on Gram-negative organisms than the first and second generation drugs, but like the second generation may require testing to determine sensitivity.

Third generation drugs are, cefotaxime, moxalactam, cefoperazon, ceftiaoxime, ceftazidime, ceftriaxone, cefitofur, and cefixime. Several of the second and third generation drugs are given
by routes other than oral.

Cephalosporins have wide distribution to tissues, bone, pleural fluid, pericardial and synovial fluid, but do not penetrate prostatic tissue or aqueous humor well. They cross the placental and fetal barriers and are found in breast milk.
They are excreted by the kidneys via tubular and glomerular filtration. A few are metabolized in the liver.

More information may be found on a specific drug of this class, used in pet rats, listed under Cephalosporins on the Rat Medication Guide.