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Home / Drugs / Starting with P / Penicillin G
Penicillin G

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.
Benzylpenicillin G
Benzylpenicillinic Acid
Compocillin G
Crysticillin 300 A.S.
Free Benzylpenicillin
Free Penicillin G
Free Penicillin Ii
Pencillin G
Penicillin G Potassium
Penicillin G Potassium in Plastic Container
Penicillin G Sodium
Penicillin-G Potassium
Penicillinic Acid, Benzyl-
Pentids '200'
Pfizerpen G
Phenylacetamidopenicillanic Acid
Specilline G
CategoriesAnti-Bacterial Agents
ManufacturersKing pharmaceuticals inc
Wyeth ayerst laboratories
Pfizer laboratories div pfizer inc
Teva pharmaceuticals usa inc
Mylan pharmaceuticals inc
Purepac pharmaceutical co
Apothecon sub bristol myers squibb co
Apothecon inc div bristol myers squibb
App pharmaceuticals llc
Consolidated pharmaceutical group inc
Gc hanford manufacturing co
Eli lilly and co
Marsam pharmaceuticals llc
Parke davis div warner lambert co
Sandoz inc
Baxter healthcare corp
Ivax pharmaceuticals inc sub teva pharmaceuticals usa
Bristol myers squibb spa
John d copanos and co inc
Pharmacia and upjohn co
PackagersAPP Pharmaceuticals
Baxter International Inc.
C.O. Truxton Inc.
King Pharmaceuticals Inc.
Pfizer Inc.
Physicians Total Care Inc.


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.


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.

mechanism of action

By binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall, penicillin G inhibits the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins; it is possible that penicillin G interferes with an autolysin inhibitor.


Oral LD50 in rat is 8900 mk/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.


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.


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.

half life

In adults with normal renal function is reportedly 0.4–0.9 hours

route of elimination

Penicillin G is eliminated by the kidneys. Nonrenal clearance includes hepatic metabolism and, to a lesser extent, biliary excretion.

drug interactions

Demeclocycline: Possible antagonism of action

Doxycycline: Possible antagonism of action

Mesoridazine: Increased risk of cardiotoxicity and arrhythmias

Mestranol: This anti-infectious agent could decreases the effect of the oral contraceptive

Methacycline: Possible antagonism of action

Methotrexate: The penicillin increases the effect and toxicity of methotrexate

Minocycline: Possible antagonism of action

Oxytetracycline: Possible antagonism of action

Rolitetracycline: Possible antagonism of action

Tetracycline: Possible antagonism of action

Thioridazine: Increased risk of cardiotoxicity and arrhythmias