By T. Zakosh. Brevard College.
Third-generation with a history of IgE-mediated hypersensitivity to one cephalosporins are less active against staphylococci than -lactam antibiotic plus positive results from a peni- the earlier generations buy ampicillin 500 mg with visa. Among patients who report penicillin allergies, 80 to 90% have negative results from peni- O cillin skin tests, and 98% tolerate subsequent -lactam S antibiotic treatments. A careful history may discrimi- R C N H nate between nonallergic reactions and true penicillin allergy and permit safe -lactam therapy. N O R′ COOH -lactam ring Dihydrothiazine ring CEPHALOSPORINS 7-aminocephalosporanic acid The cephalosporins are semisynthetic antibiotics derived from products of various microorganisms, including FIGURE 45. Con- of the cephalosporins adequately treats infections comitant ingestion of food reduces the bioavailability of caused by Enterococcus faecalis, E. The cephalosporins distribute in satisfactory con- Absorption, Distribution, Metabolism, centrations to most tissues except the central nervous and Excretion system. Only cefepime, cefuroxime (Zinacef), cefo- Most parenteral cephalosporins have good bioavailabil- taxime (Claforan), ceftriaxone (Rocephin), and cef- ity after intramuscular injection, and a few members of tazidime (Fortaz) achieve therapeutic concentrations in each cephalosporin generation have good oral bioavail- cerebrospinal ﬂuid. The ester prodrugs cefuroxime ax- tibiotics of ﬁrst choice for the empirical treatment of etil (Ceftin) and cefpodoxime proxetil (Vantin) are oral brain abscess and meningitis. Drugs like ceftriaxone Among patients with morbilliform rashes (resembling that have extensive protein binding (85–95%) may dis- measles) after penicillin, the majority (95%) will toler- place bilirubin from serum albumin. Consequently, cef- ate cephalosporins without adverse effects and with no triaxone may increase the risk of kernicterus in jaun- increased risk of anaphylaxis. The frequency of allergic reac- to patients with renal failure, practitioners must consider tions to cephalosporins is 1. Most patients with negative penicillin skin tests some cephalosporins, and an increase in cephalosporin may receive cephalosporins safely. Cephalosporins triaxone achieve biliary concentrations greater than have been associated with superinfections with those in plasma. After parenteral administration of cef- Clostridium difﬁcile, enterococci, MRSA, coagulase- operazone, 70% of the dose appears in the bile within 24 negative staphylococci, P. Cefotaxime is losporins induce production of extended-spectrum - one of the few cephalosporins having an active metabo- lactamases (ESBLs) in P.
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