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Ampicillin, Amoxicillin, Piperacillin, Ticarcillin

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Aminopenicillins (such as ampicillin and amoxicillin) are a subgroup of penicillin antibiotics characterized by an amino group that enhances their spectrum of activity against gram-negative bacteria, while anti-pseudomonal penicillins (such as piperacillin and ticarcillin) specifically target Pseudomonas aeruginosa and other gram-negative pathogens.These antibiotics all contain a beta-lactam ring and exert their bactericidal effects by binding to penicillin-binding proteins (PBPs) in the bacterial cell wall, inhibiting peptidoglycan synthesis and leading to cell death. Amino-penicillins have an expanded spectrum of activity due to their enhanced ability to penetrate the gram-negative outer membrane, making them effective against both gram-positive and gram-negative bacteria.

Notable members of this subgroup include amoxicillin, favored for its oral absorption and frequent use in treating strep throat, sinusitis, otitis, and respiratory tract infections. Additionally, amoxicillin plays a role in H. pylori eradication and early-stage Lyme disease treatment. Pairing amino-penicillins with beta-lactamase inhibitors, like clavulanate, helps overcome bacterial resistance. For more severe infections, ampicillin is administered intravenously to target anaerobes and enterococci.

Piperacillin and ticarcillin, two extended-spectrum penicillins also often paired with beta-lactamase inhibitors, effectively cover pseudomonas and anaerobes, making them valuable in hospital-acquired infections and severe respiratory illnesses like pneumonia. However, they come with their own potential side effects like skin rashes, Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), and liver injury.

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What is the mode of action of aminopenicillins and extended-spectrum penicillins?

Aminopenicillins, which include amoxicillin and ampicillin, along with extended-spectrum penicillins like piperacillin and ticarcillin, operate by binding to penicillin-binding proteins (PBPs) which effectively halts the synthesis of peptidoglycan walls. This mechanism of action makes these antibiotics effective against gram-positive organisms such as Staphylococcus and Streptococcus, and gives them improved activity against gram-negative bacteria.

What infections are typically treated with amoxicillin?

Amoxicillin, a broad spectrum antibiotic with good oral bioavailability, is commonly used to treat conditions such as streptococcal pharyngitis (strep throat), otitis media, and sinusitis, often caused by bacterial organisms like Strep pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. In addition, it can be used to treat pneumonia and is used to combat Helicobacter pylori infections or Lyme disease.

What are some common uses of ampicillin?

Ampicillin, a type of aminopenicillin drug, is effective against anaerobic infections such as aspiration pneumonia and infections caused by Enterococcus. Despite resistance from beta-lactamase producing strains of Enterococcus, it still treats a range of infections, including meningitis due to Listeria monocytogenes. Ampicillin is also used against gastrointestinal and urinary tract gram-negative bacilli (e.g. E. coli).

What are the resistance mechanisms that can impact the effectiveness of aminopenicillins and extended-spectrum penicillins?

Bacteria that are capable of producing beta-lactamase can resist the effects of both aminopenicillins and extended-spectrum penicillins. There are certain medications however, such as clavulanate, sulbactam, and tazobactam, which are often combined with these types of penicillins, to counteract this resistance mechanism, as they act as beta-lactamase inhibitors.

What are potential side effects to be aware of when prescribing aminopenicillins?

While amoxicillin and ampicillin are generally safe and effective, they do come with potential side effects. For instance, these antibiotics may cause Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) or induce liver injury. In addition, a rash can occur, especially in patients with viral illnesses such as Epstein-Barr virus (i.e. infectious mononucleosis).