Antibiotics

The term antibiotics is a broad one , defined by Waksman as, "a substance produced by microorganisms , which has the capacity of inhibiting the growth and even of destroying other microorganisms by the action of very small amounts of the antibiotics " . Approximately 3000 substances come under the classification , but only 70 have the necessary combination of patient safety , antimicrobial action and stability. Penicillin, erythromycin, tetracycline, cephalosporins are among the most widely used.

Penicillin :

A number of penicillin, differing only in the composition of the R ( alkyl ) group, have been isolated from natural media and hundreds have been semi-synthesized . Penicillin G USP, with benzyl for R group, generally the most desirable , is the type commercially available , usually combined in salt form with procaine or potassium.

 It is possible to assist the synthesis of a desired penicillin by supplying the appropriate precursor to the culture i.e., the acid of the side chain which appears the amide linkage with 6-aminopenicillanic acid in the final product. to produce benzyl-penicillin, the precursor phenylacetic acid is used.

 Erythromycin :

Erythromycin , like penicillin, also isolated by solvent-extraction methods. It is an organic base, and extract able with amyl acetate or other organic solvents under basic conditions rather than the acidic ones which favor penicillin extraction.

Streptomycin :

The commercial method for producing this compound is also aerobic submerged fermentation .

The structure of streptomycin indicates its highly hydrophilic nature, and it can not be extracted by normal solvent procedures . Because of the strong-base characteristics of the two substituted guanidine groups , it may be treated as a cation and removed from the filtered solution by ion-exchange techniques . 

Cephalosporins : 

Cephlosporins were marketed in the late 1950's when penicillin-fast organisms become prevalent . Later, chemically modified cephalosporins were developed to broaden the scope of their use and to be used where the originals were losing their effectiveness . At present several third generation cephalosporins are awaiting Food and Drug Administration approval.