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Pharmacology => Drug => Penicillin
Penicillin
INTRODUCTION
Penicillin, any one of a group of antibiotics derived from the fungus Penicillium or created by using partially artificial processes. The action of natural penicillin was first observed in 1928 by British bacteriologist Sir Alexander Fleming, but another ten years passed before penicillin was concentrated and studied by British biochemist Ernst Chain, British pathologist Sir Howard Florey, and other scientists.
Penicillin acts both by killing bacteria and by inhibiting their growth. It does not kill organisms in the resting stage but only those growing and reproducing. Penicillin is effective against a wide range of disease-bearing microorganisms, including pneumococci, streptococci, gonococci, meningococci, the clostridium that cause tetanus, and the syphilis spirochete. The drug has been successfully used to treat such deadly diseases as endocarditis, septicemia, gas gangrene, gonorrhea, and scarlet fever.
Toxic symptoms produced by penicillin are limited largely to allergic reactions that can be anticipated by the use of scratch tests before administration of the drug. In 1980 a group of physicians announced that they had successfully desensitized several penicillin-allergic patients with a procedure that took only three hours; tests of the method on a wider scale were instituted.
SEMISYNTHETIC PENICILLIN
Despite the effectiveness of penicillin in curing a wide range of diseases, infections caused by certain strains of staphylococci cannot be cured by the antibiotic because the organism produces an enzyme, penicillinase, capable of destroying the antibiotic. In addition, enterococci and other bacteria known to cause respiratory and urinary tract infections were found intrinsically resistant to the action of penicillin. Appropriate chemical treatment of a biological precursor to penicillin, isolated from bacterial cultures, resulted in the formation of a number of so-called semisynthetic penicillins. The most important of these are methicillin and ampicillin-the former is remarkably effective against penicillinase-producing staphylococci and the latter is not only active against all organisms normally killed by penicillin, but also inhibits enterococci and many other bacteria.
DOSAGES
The strength and dosage of penicillin are measured in terms of international units. Each of these units is equal to 0.0006 g of the crystalline fraction of penicillin called penicillin G. In the early days of penicillin therapy, the drug was administered every three hours in small doses. More recently, a preparation called benzathine penicillin G has been produced that provides detectable levels of antibiotic for as long as four weeks after a single intramuscular injection; it is useful for treatment of syphilis and strep throat. Bacterial resistance to some penicillins has increased over the years, creating a need for alternative therapies.
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