cephalosporins

cephalosporins
Use	Antibacterial
ATC prefix	J01D
Biological target	Penicillin-binding proteins
Synonyms	Cephems

cephalosporins are a class of beta-lactam antibiotics originally derived from the fungus *Acremonium* (formerly *Cephalosporium*). They are structurally and functionally related to penicillins and are used to treat a wide array of bacterial infections. Their development, characterized by distinct "generations," has been a major advancement in antimicrobial chemotherapy, providing critical tools against evolving antimicrobial resistance.

Classification and generations

Cephalosporins are systematically categorized into five generations based on their antimicrobial spectrum and chronological development. First-generation agents, such as cefazolin and cephalexin, are primarily effective against Gram-positive bacteria including *Staphylococcus aureus* and some Gram-negative bacteria like *Escherichia coli*. The second generation, including cefoxitin and cefuroxime, exhibits enhanced activity against Haemophilus influenzae and Moraxella catarrhalis. Third-generation cephalosporins like ceftriaxone and cefotaxime provide superior coverage against Enterobacteriaceae and are pivotal in treating meningitis and hospital-acquired infections. Fourth-generation drugs such as cefepime combine broad Gram-negative coverage with retained anti-staphylococcal activity. Fifth-generation agents, exemplified by ceftaroline, are uniquely active against methicillin-resistant Staphylococcus aureus (MRSA) and multi-drug resistant Streptococcus pneumoniae.

Medical uses

These antibiotics are employed across diverse clinical settings, from outpatient clinics to intensive care units. They are standard therapy for community-acquired pneumonia, skin and soft tissue infections, and urinary tract infections. Specific agents are crucial in surgical prophylaxis, with cefazolin commonly used for procedures like coronary artery bypass grafting. In obstetrics and gynecology, they treat pelvic inflammatory disease and prevent postpartum infection. For serious conditions such as bacterial meningitis and sepsis, later-generation drugs like ceftriaxone are first-line choices. Their use is guided by institutions like the World Health Organization and local antimicrobial stewardship programs to ensure appropriate application.

Mechanism of action

Cephalosporins exert their bactericidal effect by inhibiting bacterial cell wall synthesis. They bind to specific penicillin-binding proteins (PBPs) located in the bacterial cell membrane. This binding disrupts the final transpeptidation step in the synthesis of peptidoglycan, a critical component of the cell wall. The inhibition leads to the activation of autolytic cell wall enzymes and ultimately causes cell lysis and bacterial death. This mechanism is analogous to that of penicillins but the distinct chemical structure of cephalosporins allows them to resist degradation by many beta-lactamase enzymes, broadening their spectrum of activity.

Adverse effects and resistance

Common adverse reactions include gastrointestinal disturbances such as nausea and diarrhea, and hypersensitivity reactions ranging from skin rash to severe anaphylaxis. Cross-reactivity with penicillin allergy is a significant concern. More serious effects can include Clostridioides difficile infection, neutropenia, and drug-induced liver injury. Resistance arises primarily through bacterial production of beta-lactamase enzymes, such as extended-spectrum beta-lactamases (ESBLs) and AmpC beta-lactamases, which hydrolyze the beta-lactam ring. Additional mechanisms include alterations in PBPs, as seen in MRSA, and reduced permeability of the outer membrane in Gram-negative bacteria. The spread of resistant strains is monitored globally by agencies like the Centers for Disease Control and Prevention.

History and development

The discovery traces to 1945 when Italian pharmacologist Giuseppe Brotzu isolated the fungus *Cephalosporium acremonium* from seawater near a Sassari sewer outfall. Initial purification work was conducted at the University of Oxford by a team including Edward Abraham and Guy Newton, leading to the isolation of cephalosporin C. The first therapeutic agent, cephalothin, was introduced into clinical practice in the 1960s by the pharmaceutical company Eli Lilly and Company. Subsequent generations were developed in response to the rising threat of beta-lactamase-producing bacteria, with significant contributions from researchers at institutions like Merck & Co. and GlaxoSmithKline. This history is closely tied to the broader narrative of the antibiotic era.

Chemical structure and properties

The core structure is the cephem nucleus, consisting of a beta-lactam ring fused to a six-membered dihydrothiazine ring, which distinguishes it from the penam nucleus of penicillins. This 7-aminocephalosporanic acid (7-ACA) core is produced semi-synthetically and can be modified at two key sites: the R1 side chain at the 7-position influences beta-lactamase stability and PBP affinity, while the R2 side chain at the 3-position affects pharmacokinetics and antibacterial potency. These modifications, pioneered by chemical methods from organizations like the Massachusetts Institute of Technology, yield compounds with varying acid stability, protein binding, and abilities to penetrate the blood–brain barrier.

Category:Antibiotics Category:Drug classes