Penicillin G

Absorption

Rapidly absorbed following both intramuscular and subcutaneous injection. Initial blood levels following parenteral administration are high but transient. Oral absorption in fasting, healthy humans is only about 15-30% as it is very susceptible to acid-catalyzed hydrolysis.

Toxicity

Oral LD50 in rat is 8900 mg/kg . Neurological adverse reactions, including convulsions, may occur with the attainment of high CSF levels of beta-lactams. Neutropenia can occur if high doses are administered consistently for over 2 weeks.

Description

Penicillin was the first natural antibiotic used to treat bacterial infections and continues to be one of the most important antibiotics.The name comes from the fungus genus Penicillium from which it was isolated. Penicillus is Latin for brush and refers to the brushlike appearance of filamentous Penicillium species.Species of this genus are quite common and appear as the bluish-green mold that appears on aged bread, fruit, and cheese. The term penicillin is a generic term that refers to a number of antibiotic compounds with the same basic structure. Therefore it is more appropriate to speak of penicillins than of penicillin.
The general penicillin structure consists of a β-lactam ring and thiazolidine ring fused together with a peptide bonded to a variable R group. Penicillin belongs to a group of compounds called β-lactam antibiotics. This in turn inhibits the formation of peptidoglycan cross-links in bacteria cell walls.

Description

The “wonder drug” penicillin is actually a group of drugs that have different functional groups on one of the side chains on the bicyclic core. In 1928, Scottish biologist Alexander Fleming isolated the first specific form of penicillin from Penicillium fungi; the compound is known variously as benzylpenicillin, penicillin G, or benzylpenicillinic acid. For this achievement, Fleming shared the 1945 Nobel Prize in Physiology or Medicine.
The free acid benzylpenicillin is only sparingly soluble in water; but even worse, it is inactivated by water. Thus, the articles of commerce are its sodium and potassium salts, which are much more water-soluble and stable in solution.
By the beginning of World War II, penicillin had been developed into antibacterial drugs that could be mass-produced. At the time of the Normandy invasion in 1944, more than 2 million doses had been made. Penicillin may have saved as many as 100,000 lives during the war.
Much more recently, it was discovered that some soil bacteria readily consume penicillin and other β-lactam antibiotics. Biologist Gautam Dantas and his team at Washington University (St. Louis) hypothesized that bacteria engineered to maximize β-lactam consumption capacity could be used to remediate antibiotic-contaminated soils.
The researchers created a strain of Escherichia coli that uses penicillin as its only carbon source. The downside, however, is that other organisms might also acquire the degradation genes and become resistant to penicillin.

The Uses of Penicillin G

Antibacterial.

Background

Benzylpenicillin (Penicillin G) is narrow spectrum antibiotic used to treat infections caused by susceptible bacteria. It is a natural penicillin antibiotic that is administered intravenously or intramuscularly due to poor oral absorption. Penicillin G may also be used in some cases as prophylaxis against susceptible organisms.
Natural penicillins are considered the drugs of choice for several infections caused by susceptible gram positive aerobic organisms, such as Streptococcus pneumoniae, groups A, B, C and G streptococci, nonenterococcal group D streptococci, viridans group streptococci, and non-penicillinase producing staphylococcus. Aminoglycosides may be added for synergy against group B streptococcus (S. agalactiae), S. viridans, and Enterococcus faecalis. The natural penicillins may also be used as first or second line agents against susceptible gram positive aerobic bacilli such as Bacillus anthracis, Corynebacterium diphtheriae, and Erysipelothrix rhusiopathiae. Natural penicillins have limited activity against gram negative organisms; however, they may be used in some cases to treat infections caused by Neisseria meningitidis and Pasteurella. They are not generally used to treat anaerobic infections. Resistance patterns, susceptibility and treatment guidelines vary across regions.

Indications

For use in the treatment of severe infections caused by penicillin G-susceptible microorganisms when rapid and high penicillin levels are required such as in the treatment of septicemia, meningitis, pericarditis, endocarditis and severe pneumonia.

Pharmacokinetics

Penicillin G is a penicillin beta-lactam antibiotic used in the treatment of bacterial infections caused by susceptible, usually gram-positive, organisms. The name "penicillin" can either refer to several variants of penicillin available, or to the group of antibiotics derived from the penicillins. Penicillin G has in vitro activity against gram-positive and gram-negative aerobic and anaerobic bacteria. The bactericidal activity of penicillin G results from the inhibition of cell wall synthesis and is mediated through penicillin G binding to penicillin binding proteins (PBPs). Penicillin G is stable against hydrolysis by a variety of beta-lactamases, including penicillinases, and cephalosporinases and extended spectrum beta-lactamases.

Metabolism

About 16-30% of an intramuscular dose is metabolized to penicilloic acid, an inactive metabolite. Small amounts of 6-aminopenicillanic acid have been recovered in the urine of patients on penicillin G. A small percentage of the drug appears to be hydroxylated into one or more active metabolites, which are also excreted via urine.