Master Aminopenicillins Mechanism of Action

Aminopenicillins have a wider spectrum of coverage than penicillins because they can cover some gram-negative bacteria, like Escherichia coli and Haemophilus influenzae.

Ampicillin is a beta-lactam antibiotic in the aminopenicillin family. It can be used against gram-positive organisms and limited gram-negative bacteria. It can sometimes cause a rash if accidentally used for patients with mononucleosis.

Amoxicillin is a popular oral beta-lactam antibiotic used for infections such as otitis media, skin infections, and strep throat. It is susceptible to degradation by beta-lactamase-producing bacteria and is, therefore, often combined with beta-lactamase inhibitors like clavulanic acid.

Beta-lactamase is an enzyme produced by some bacteria to cleave beta-lactam antibiotics, rendering them ineffective. When an antibiotic is described as beta-lactamase-sensitive, it means it is likely ineffective against beta-lactamase-producing bacteria. Beta-lactamase inhibitors are commonly combined with penicillin-group antibiotics to overcome resistance to these enzymes. Commonly used beta-lactamase inhibitors include clavulanic acid, sulbactam, and tazobactam

Clavulanic acid is a beta-lactamase inhibitor commonly combined with penicillin-group antibiotics to overcome resistance in bacteria that secrete beta-lactamase, which inactivates most penicillins. Clavulanic acid shares a similar beta-lactam ring structure and is known as a suicide inhibitor because it covalently binds to the active site of beta-lactamase, thereby inactivating it. Clavulanic acid is commonly combined with amoxicillin and marketed under the name Augmentin

Because penicillin and aminopenicillins are relatively similar in structure, individuals with hypersensitivity reactions to penicillins may also demonstrate a hypersensitivity or anaphylactic reaction to aminopenicillins. A hypersensitivity or anaphylactic reaction is an overreaction of the body's immune response. Symptoms may include rashes, hives, itchy eyes, and a swollen tongue or face.

Patients with infectious mononucleosis caused by the Epstein-Barr virus are sometimes misdiagnosed with streptococcal pharyngitis due to the similarity of symptoms and are given antibiotics like ampicillin. About 80-90% of patients with acute Epstein-Barr virus infection treated with ampicillin develop a diffuse red rash called ampicillin rash.

Ampicillin is associated with pseudomembranous colitis, an infection of the colon characterized by foul-smelling diarrhea, fever, and abdominal pain caused by Clostridioides (formely known as Clostridium) difficile infection. Ampicillin is known to be an antibiotic that can precipitate pseudomembranous colitis due to a broad spectrum that can destroy normal gut flora, allowing the gut to be overrun with C. difficile.