cephalosporin, any of a group of β-lactam antibiotics that inhibit the synthesis of a structural component of the bacterial cell wall. The cephalosporins were first isolated from cultures of the fungus Cephalosporium acremonium. Modifications of the β-lactam ring have resulted in more than 20 derivatives with a range of antibacterial properties. The cephalosporins are often used as an alternative in patients who are sensitive to penicillin.
The cephalosporins have been organized into groups based roughly on their activity. First-generation cephalosporins (e.g., cephalothin and cefalozin) tend to be broad-spectrum antibiotics that are effective against gram-positive and many gram-negative bacteria, including Staphylococcus, Streptococcus, and many strains of Escherichia coli. They have also been used to fight pulmonary infections caused by Klebsiella pneumoniae.
Second-generation cephalosporins (e.g., cefuroxime and cefamandole) and third-generation ones (such as ceftazidime) tend to be more effective against gram-negative bacterial species that are resistant to the first-generation cephalosporins. Second-generation cephalosporins have proven effective against gonorrhea, Haemophilus influenzae, and the abscesses caused by Bacteroides fragilis. The ability of many cephalosporin derivatives to penetrate the cerebral spinal fluid makes them effective in treating meningitis.