Antibiotics - Penicillins: Nursing pharmacology

Penicillins are antibiotics that got their name from the Penicillium mold, from which they were originally extracted. They belong to the pharmacological group of beta-lactam antibiotics, because they have a beta-lactam ring in their structure. Penicillins are used to treat a wide range of infections, including streptococcal infections, like pharyngitis, tonsillitis, scarlet fever, and endocarditis; as well as pneumococcal infections; staphylococcal infections; diphtheria; anthrax; and syphilis.

Now, to build their cell walls, bacteria need an enzyme called DD-transpeptidase, or penicillin binding protein, or PBP for short. Penicillins, like all beta lactam antibiotics, bind to this enzyme thanks to their beta-lactam ring, and prevent it from working.

Now, some bacteria have developed resistance to beta lactam antibiotics. The most notable is Staphylococcus aureus, which has developed an enzyme called beta-lactamase or penicillinase, that breaks down the beta-lactam ring within the antibiotic, rendering it ineffective.

So, penicillins are further classified into four groups: basic penicillins, broad-spectrum or aminopenicillins, penicillinase-resistant or antistaphylococcal penicillins, and extended-spectrum or antipseudomonal penicillins.

Basic penicillins include penicillin V, which is given orally, and penicillin G, which is administered intramuscularly or intravenously. In addition, there’s a specific penicillin G called penicillin G benzathine, which is a long-acting penicillin that’s only administered intramuscularly. These are quite effective against common gram-positive bacteria, so they’re used to treat upper respiratory infections, otitis media, pneumonia, rheumatic fever, erysipelas, skin and soft-tissue infections, and STIs like syphilis. However, they don’t work well against most gram-negative bacteria.

On the other hand, broad spectrum penicillins include amoxicillin, which is given orally, and ampicillin, which is administered orally, intramuscularly, or intravenously. They’re effective against a wide variety of gram-negative bacteria, so they’re useful to treat respiratory, gastrointestinal, genitourinary, and skin infections. Ampicillin is also useful for more serious infections that require an intravenous administration, like meningitis, endocarditis, and septicemia.

Next are penicillinase-resistant medications, or antistaphylococcal penicillins; these include dicloxacillin, which is given orally, as well as nafcillin and oxacillin, which are administered intramuscularly or intravenously. They were created to fight bacteria like Staphylococcus aureus, which often have the beta-lactamase enzyme making them resistant to other penicillins.

Finally, there’s piperacillin, an extended-spectrum penicillin which is combined with tazobactam, a beta-lactamase inhibitor, that’s administered intravenously. This medication combination has more gram-negative coverage. Most notably, it’s effective against Pseudomonas aeruginosa. That’s why it’s also called an antipseudomonal penicillin.

Penicillins are generally safe and well tolerated. The most common side effects include gastrointestinal disturbances, like nausea, vomiting, and diarrhea.

In addition, allergy to penicillins is quite common, and clients typically present with urticaria, pruritus, and anaphylaxis.

Other serious side effects of penicillins include hypersensitivity reactions Stevens-Johnson syndrome and erythema multiforme. Some clients taking penicillins may even experience seizures, especially when taking high doses.

In addition, penicillins can also affect the healthy bacterial flora, making clients more susceptible to superinfections by more resistant pathogens, including fungal infections like vaginitis and candidiasis, and more rarely, Clostridioides difficile infection or CDI for short.

More specifically, a very frequent side effect of penicillin G is pain at the site of injection. In addition, accidental intra-arterial injection or injection near a major peripheral nerve can result in severe neurovascular damage and tissue necrosis. Amoxicillin can cause eosinophilia, anemia, and thrombocytopenia. Finally, some penicillins can cause interstitial nephritis and renal tubular damage.