Cephalosporins are a large group of antibiotics derived from the mold Acremonium (previously called Cephalosporium). This mold yielded three main compounds, historically called Cephalosporin N and C, and P, from which the first cephalosporins were derived.
Cephalosporins are bactericidal (kill bacteria) and work in a similar way to penicillins. They bind to and block the activity of enzymes responsible for making peptidoglycan, an important component of the bacterial cell wall. They are called broad-spectrum antibiotics because they are effective against a wide range of bacteria.
Since the first cephalosporin was discovered in 1945, scientists have been improving the structure of cephalosporins to make them more effective against a wider range of bacteria. Each time the structure changes, a new "generation" of cephalosporins are made. So far there are five generations of cephalosporins. All cephalosporins start with cef, ceph, or kef. Note that this classification system is not used consistently from country to country.
Fourth generation cephalosporins refer to the fourth group of cephalosporins discovered. They are structurally related to third-generation cephalosporins but possess an extra ammonium group, which allows them to rapidly penetrate through the outer membrane of Gram-negative bacteria, enhancing their activity. They are also active against β-lactamase producing Enterobacteriaceae which may inactivate third-generation cephalosporins.
Some fourth-generation cephalosporins have excellent activity against gram-positive bacteria such as methicillin-susceptible staphylococci, penicillin-resistant pneumococci and viridans group streptococci.
Cefepime is the only fourth generation cephalosporin available in the United States. Cefpirome is available overseas.
