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Cephalosporins belong to β-lactam antibiotics and are one of the largest classes of antimicrobial preparations. Currently five generations of cephalosporins may be distinguished, among which the first 3 are preparations which may be used both parenterally and orally. Due to high effectiveness of the drugs and low toxicity figures, the drugs are among the most frequently used antimicrobial preparations. In clinical treatment the preparations are indicated according to their antimicrobial activity which differs strongly in cephalosporins of different generations. Structural similarity among penicillins and cephalosporins determine the mutual mechanism of antimicrobial effect and possibility of cross -resistance and allergic reactions in some of the patients.
The preparation exert bactericidal effects in the same way as other beta-lactam antibiotics, but in comparison with penicillins cephalosporins are less susceptible to penicilinases. Their mechanism of action consists in synthesis disruption of the peptidoglycan layer in the bacterial cell wall, thus affecting the structural integrity of the bacterial cell and killing it.
Oral cephalosporins are easily absorbed int eh GI tract. Bioavailability of the preparations, however strongly depends on the preparations and varies from 40-50% in cefexime to 95% in cefalexin and etc. The absorption of certain cephalosporin antibiotics can be slowed down if administered with food, on the other hand other cepahlosporins, like cefuroxime axetil during absorption is transformed into the active metabolite and food promotes this transformation.
Cephalosporins possess high affinity to tissues and organs (except prostate gland). High concentrations of the drugs are found in the lungs, kidneys, liver, muscles, skin, soft tissues, bones and internal fluids. The highest concentrations in bile are produced by ceftriaxone and cefoperazone. The ability to pass the blood-brain barrier is mostly expressed in III and IV generation cephalosporins.
The majority of cephalosporins are not metabolized. Amongst exceptions is cefotaxime, which is transformed into its active metabolite in the body. The drug is excreted via kidneys, therefore very high concentrations of cephalosporins are registered in the urine. The half-life of the drugs varies significantly in each unique case from 1-2 hours for the majority of drugs to 8,5 hours in ceftriazone, which due to that can be administered once a day. In renal insufficiency the dosages of cephalosporins administered should be corrected.
Common properties which may be pointed for all the 5 classes of cephalosporines are:
Normally cephalosporins are well tolerated, which is one of the reasons they are so widely used. However as any other drug cephalosporins may exert specific adverse effects: