An alternative spelling of cefalexin, a common cephalosporin drug.
Penicillin was the ?rst antibiotic to be discovered and used in the 1940s. The discovery and isolation in 1958 of the penicillin nucleus, 6-amino penicillanic acid (6-PNA), allowed many new penicillins to be synthesised. These are now the largest single group of antibiotics used in clinical medicine. Most staphylococci (see STAPHYLOCOCCUS) have now developed resistance to benzylpenicillin, the early form of the drug, because they produce penicillinases – enzymes which break down the drug. Other types of penicillin such as cloxacillin and ?ucoxacillin are not affected and are used against penicillin-resistant staphylococci.
The cephalosporins are derived from the compound cephalosporin C, which is obtained by fermentation of the mould cephalosporium.
The cephalosporin nucleus 7 amino cephalosporanic (7-ICA) acid has been the basis for the production of the semi-synthetic compounds of the cephalosporin nucleus. The ?rst semi-synthetic cephalosporin, cephalothin, appeared in 1962; it was followed by cephaloridine in 1964. The original cephalosporins had to be given by injection, but more recent preparations can be given by mouth. The newer preparations are less readily destroyed by betalactamases and so they have a much broader spectrum of antibacterial activity. The newer cephalosporins include cephalexin, cefazolin, cephacetrile, cephapirin, cefamandole, cefuroxine, cephrodine, cefodroxil and cefotaxine. Inactivation of beta-lactamase is the basis of bacterial resistance both to the penicillins and to the cephalosporins, so that attempts to prepare these antibiotics with resistance to betalactamase is of great importance. A synthetic inhibitor of beta-lactamase called clavulanic acid has been synthesised; this is used in combination with the penicillins and cephalosporins to prevent resistance. The cephamycins are a new addition to the beta-lactam antibiotics. They are similar in structure to the cephalosporins but are produced, not by fungi, but by actinomycetes.
Overuse and misuse of antibiotics have resulted in many bacteria becoming resistant to them. Hospitals, in particular, have problems with METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA). Combinations of antibiotics are needed to combat resistant strains of bacteria, another example being Mycobacterium tuberculosis.... antibiotics
First-generation examples still in use include cephalexin and cefadroxil. They are orally active and, along with second-generation cefaclor, have a similar antimicrobial spectrum. They are used for ‘resistant’ urinary infections and urinary infections in pregnancy. Cephalosporins have a similar pharmacology to that of penicillin, and about 10 per cent of patients allergic to penicillin will also be hypersensitive to cephalosporins. They are e?ective in treating SEPTICAEMIA, PNEUMONIA, MENINGITIS, biliary-tract infections and PERITONITIS.
Second-generation cefuroxime and cefamandole are less vulnerable to penicillinases and are useful for treating ‘resistant’ bacteria and Haemophilus in?uenzae and Neisseria gonorrhoea. Third-generation cephalosporins include cefotaxime, ceftazidime and others; these are more e?ective than the second-generation in treating some gram-negative infections, especially those causing septicaemia.... cephalosporins
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