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A hypersensitivity reaction to penicillin, present in about 0.5% to 8% of the population. Although different types of hypersensitivity reactions may occur, the most common and potentially dangerous are the type I (immediate) reactions mediated by immunoglobulin E. If a patient reports a history of signs of local anaphylaxis (such as urticaria) or systemic anaphylaxis (such as bronchoconstriction, vasodilation) after taking penicillin, no penicillin or other beta-lactam antibiotics (such as cephalosporins) should be given to that patient ever again. In those very rare situations in which an infection is susceptible to no other antibiotic and the infection is serious enough to risk the danger of anaphylaxis, the patient may be desensitized with gradually increasing doses of penicillin.
See also: allergy
any of a large group of natural or semisynthetic antibacterial antibiotics derived directly or indirectly from strains of fungi of the genus Penicillium and other soil-inhabiting fungi grown on special culture media. Penicillins exert a bactericidal as well as a bacteriostatic effect on susceptible bacteria by interfering with the final stages of the synthesis of peptidoglycan, a substance in the bacterial cell wall. Despite their relatively low toxicity for the host, they are active against many bacteria, especially gram-positive pathogens (streptococci, staphylococci); clostridia; certain gram-negative forms; certain spirochetes (Treponema pallidum and T. pertenue); and certain fungi. Certain strains of some target species, for example staphylococci, secrete the enzyme penicillinase, which inactivates penicillin and confers resistance to the antibiotic. Some of the newer penicillins, for example methicillin, are more effective against penicillinase-producing organisms. An additional class of extended-spectrum penicillins has been approved for use; it includes piperacillin and mezlocillin.
There are four groups of penicillins, the natural penicillins, penicillin G and penicillin V, with a narrow spectrum of activity, mainly against gram-positive bacteria; the aminopenicillins (amoxicillin, ampicillin and hetacillin) are semisynthetic derivatives and have a broad spectrum of activity against gram-positive and many gram-negative organisms, but are susceptible to penicillinase-producing Staphylococcus spp.; penicillinase-resistant penicillins, which include cloxacillin, methicillin, nafcillin and oxacillin; and the extended-spectrum penicillins (azlocillin, carbenicillin, mezlocillin, piperacillin and ticarcillin), which are effective against gram-positive and gram-negative organisms, including Pseudomonas aeruginosa.
Allergic reaction to penicillin occurs in some animals. The reaction may be slight—a stinging or burning sensation at the site of injection—or it can be more serious—severe dermatitis or even anaphylactic shock, which may be fatal.
degradation products of the penicillins act as haptens, binding to proteins and stimulating an immune response.
benzylpenicillin; the most widely used penicillin; used principally in the treatment of infections due to gram-positive bacteria. Procaine penicillin G is a parenteral preparation that gives extended action for up to 24 hours and benzathine penicillin G is a very slow-release, parenteral preparation that maintains blood levels for several days.
penicillin-induced hemolytic anemia
rare problem in horses which develop IgG anti-penicillin antibodies.
a biosynthetically or semisynthetically produced antibiotic, similar to penicillin G, for oral administration; not affected by gastric acid and is suitable for oral administration. Its antibacterial spectrum is the same as for penicillin G. Called also penicillin V.
see phenoxymethyl penicillin (above).