💊 Penicillins

Penicillins are a broad class of beta-lactam antibiotics, derived from the Penicillium mould. They are bactericidal and widely used to treat a variety of bacterial infections.

Penicillins exert their bactericidal effect by inhibiting bacterial cell wall synthesis. They bind to and inactivate penicillin-binding proteins (PBPs), which are enzymes involved in the cross-linking of peptidoglycan chains, a crucial component of the bacterial cell wall. This leads to weakened cell walls, osmotic lysis, and bacterial death.

Penicillins are indicated for a wide range of bacterial infections, including respiratory tract infections (e.g., pneumonia, tonsillitis), skin and soft tissue infections (e.g., cellulitis), urinary tract infections, and sexually transmitted infections (e.g., syphilis). Specific penicillins are chosen based on the suspected pathogen and its susceptibility. Examples include penicillin V, amoxicillin, flucloxacillin, and co-amoxiclav.

The absolute contraindication for penicillins is a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, angioedema) to any penicillin. Caution is advised in patients with a history of allergy to other beta-lactam antibiotics (e.g., cephalosporins) due to potential cross-reactivity. Renal impairment may require dose adjustment.

Common adverse effects include gastrointestinal disturbances (nausea, vomiting, diarrhoea) and skin rashes (non-allergic or allergic). Serious adverse effects, though rare, include anaphylaxis, angioedema, Stevens-Johnson syndrome, and drug-induced liver injury (especially with flucloxacillin). Clostridioides difficile infection (CDI) is a risk with broad-spectrum penicillins.

Monitoring primarily involves observing for clinical improvement of the infection and any signs of adverse drug reactions, particularly allergic reactions. For prolonged courses or in patients with renal impairment, renal function may be monitored. Liver function tests may be considered with flucloxacillin, especially in prolonged treatment.

ALWAYS ask about penicillin allergy, clarifying the nature of any previous reaction. Document this clearly. Counsel patients on completing the full course of antibiotics and to seek immediate medical attention for signs of a severe allergic reaction (e.g., difficulty breathing, swelling). Advise on potential GI upset.

Penicillins are a cornerstone of antibiotic therapy. Crucial to differentiate true penicillin allergy from minor side effects. Flucloxacillin is key for staphylococcal infections. Co-amoxiclav has broader spectrum due to beta-lactamase inhibitor. Remember the mechanism: cell wall synthesis inhibition.

SBA questions frequently revolve around penicillin allergies, differentiating between true anaphylaxis and milder reactions. Cross-reactivity with cephalosporins is a common trap. Questions might also focus on the spectrum of activity of different penicillins (e.g., flucloxacillin for staphylococci, amoxicillin for broader coverage) or their use in specific infections.