penicillin G

penicillin G

n.

The most commonly used penicillin compound, used primarily in the form of its stable salts. Also called benzylpenicillin.

---

penicillin [pen″ĭ-sil´in]

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 bacteriocidal 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, pneumococci); clostridia; certain gram-negative forms (gonococci and meningococci); 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, such as methicillin, are more effective against penicillinase-producing organisms. A class of extended-spectrum penicillins includes piperacillin and mezlocillin.

Penicillin is administered intramuscularly, orally, in liquid or tablet form, and topically in ointments. Oral administration requires larger doses of the drug because absorption is incomplete. Allergic reactions occur in some persons. 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.

penicillin G the most widely used penicillin, used principally in the treatment of infections due to gram-positive organisms, gram-negative cocci, Treponema pallidum and Actinomyces israelii. The usual forms are salts such as penicillin benzathine, potassium, procaine, or sodium. Called also benzylpenicillin.

penicillin V a biosynthetically or semisynthetically produced antibiotic similar to penicillin g, used orally in the form of the benzathine or potassium salt for mild to moderately severe infections due to susceptible gram-positive bacteria.

---

penicillin (pen´isil´in),

n an antibiotic secured from cultures of
P. notatum, being bactericidal for gram-positive cocci, some gram-negative cocci (gonococcus and meningococcus), and clostridial and spirochetal organisms. Its topical application to the oral mucusa membranes is discouraged because of the high risk of sensitization from local application of antibiotic substances.

penicillin G,

n an acid-sensitive form of penicillin prepared as penicillin G benzathine and penicillin G procaine used for deep intramuscular administration. It is slowly released, resulting in prolonged effective blood levels. In past dentistry, it was used prophylactically for patients predisposed to bacterial endocarditis prior to any invasive dental procedure. Now it has been replaced by amoxicillin. It has a high allergy potential. See also penicillin G benzathine.

penicillin G benzathine,

n brand names: Bicillin L-A, Permapen;
drug class: benzathine salt of natural penicillin;
action: interferes with cell wall replication of susceptible organisms; osmotically unstable cell wall swells and bursts from osmotic pressure;
uses: respiratory infections, scarlet fever, erysipelas, otitis media, pneumonia, skin and soft tissue infections, and yaws.

penicillin V potassium/penicillin V,

n brand names: Beepen-VK, Betapen-VK, V-Cillin K, Veetids, others;
drug class: semisynthetic penicillin;
action: interferes with cell wall replication of susceptible organisms; the cell wall, rendered osmotically unstable, swells and bursts from osmotic pressure;
uses: effective for both gram-positive cocci and gram-negative bacilli.

---

penicillin

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.

---

penicillin allergy

degradation products of the penicillins act as haptens, binding to proteins and stimulating an immune response.

penicillin G

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.

phenoxymethyl penicillin

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.

penicillin V

see phenoxymethyl penicillin (above).