Pharmacology
Summary
Penicillin-- the famed antibiotic that was discovered by Alexander Fleming in 1928--- is a beta-lactam antibiotic that disrupts bacterial cell wall synthesis by interfering with the transpeptidation reaction. It primarily targetings gram-positive organisms, and is utilized for treating a range of bacterial infections. Penicillins operate by binding to penicillin-binding proteins (PBPs), which are involved in the formation of cross-links in the bacterial cell wall. This disrupts the synthesis of peptidoglycan in actively growing cells and causing cell death. Penicillin G is the IV form of penicillin, and is commonly used for severe infections, while Penicillin V is used for less severe infections.
Penicillin is effective primarily against gram-positive organisms like staphylococcus and streptococcus that have thick peptidoglycan walls. Clinical uses for penicillin include treating infections such as strep throat, rheumatic fever, Strep viridans, Strep agalactiae, Actinomyces israelii, Clostridium perfringes, Pasturella multocida, and syphilis.
Resistance can occur with the production of beta-lactamases that can occur in bacteria like Staph aureus. Negative side effects can include anaphylaxis due to IgE-mediated hypersensitivity, autoimmune hemolytic anemia, and interstitial nephritis. Despite these possible adverse reactions, however, penicillins are generally well-tolerated.
Lesson Outline
Don't stop here!
Get access to 133 more Pharmacology lessons & 13 more medical school learning courses with one subscription!
FAQs
Penicillin V and Penicillin G are both types of penicillin, a beta-lactam antibiotic. Penicillin G is typically administered intravenously and is used to treat infections like left-sided endocarditis caused by Strep viridans and Strep bovis, and it can also treat syphilis caused by Treponema pallidum. On the other hand, Penicillin V is acid stable and is often used to treat streptococcal pharyngitis or strep throat caused by Strep pyogenes. Both penicillin V and G can be used to treat rheumatic fever, a complication of strep throat.
Penicillin, a beta-lactam antibiotic, works by covalently binding to Penicillin-Binding Proteins (PBPs). This prevents PBPs from forming cross-links in the peptidoglycan cell wall. The peptidoglycan cell wall has repeating D-alanyl-D-alanine oligopeptides, and disabling the formation of these cross-links weakens the bacterial cell wall, ultimately causing bacterial cell death.
Penicillin is active against various gram positive organisms, such as Staphylococcus and Streptococcus. It treats infections like Actinomyces israelii, a gram positive rod bacterium that grows in chains, and Clostridium perfringens, which can cause gangrene. In the case of dog bite wounds infected with Pasteurella multocida, a gram negative coccobacillus, penicillin can also be used for treatment. It can also treat meningitis caused by Neisseria meningitidis, a gram negative diplococcus.
Some bacterial infections, such as those caused by Staph aureus, are resistant to penicillin. This resistance is due to the presence of beta-lactamases, which are enzymes that can hydrolyze the beta-lactam ring present in penicillin. These beta-lactamases are expressed by plasmid genes within the bacteria, allowing them to degrade penicillin and thus evade its antibacterial effects.
Penicillins can cause adverse reactions like Type-1 (IgE mediated) hypersensitivity reactions. Symptoms of this reaction may include urticaria, angioedema, bronchospasm, and anaphylaxis. Penicillins can also cause drug-induced autoimmune hemolytic anemia where IgG antibodies against penicillin bind to the surface of red blood cells, causing destruction of the cells. In some cases, penicillins can cause drug-induced interstitial nephritis, which is inflammation of the spaces between renal tubules in the kidneys.
