💊 Cephalosporins

Cephalosporins are a class of beta-lactam antibiotics, structurally and pharmacologically related to penicillins. They are bactericidal and are broadly categorised into 'generations' based on their antimicrobial spectrum.

Cephalosporins inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs). This binding prevents the cross-linking of peptidoglycan chains, leading to a defective cell wall and ultimately bacterial lysis.

They are widely used for a variety of bacterial infections, including respiratory tract infections, urinary tract infections, skin and soft tissue infections, and surgical prophylaxis. Different generations offer varying coverage, with later generations often having broader gram-negative activity and improved CNS penetration.

Known hypersensitivity to cephalosporins is an absolute contraindication. Caution is advised in patients with a history of severe immediate hypersensitivity reactions to penicillins, due to the potential for cross-reactivity (approximately 5-10%). Renal impairment requires dose adjustment.

Common side effects include gastrointestinal disturbances (nausea, vomiting, diarrhoea), rash, and hypersensitivity reactions. Serious but rare effects include Clostridioides difficile infection (CDI), Stevens-Johnson syndrome, and haematological abnormalities like neutropenia or thrombocytopenia.

Renal function should be monitored, especially in patients with pre-existing impairment or those receiving high doses. Liver function tests may be considered in prolonged therapy. Clinical response to treatment should be regularly assessed.

Always check for penicillin allergy and document its nature and severity; if severe, cephalosporins are generally avoided. Be aware of potential interactions with anticoagulants (e.g., warfarin, increasing INR). Counsel patients on taking the full course, potential GI upset, and to report any severe rash or diarrhoea.

First-generation cephalosporins (e.g., cefalexin) are good for Gram-positive skin infections. Second-generation (e.g., cefuroxime) have broader Gram-negative coverage. Third-generation (e.g., ceftriaxone, cefotaxime) are often used for more serious infections, including meningitis, due to better CNS penetration. Fourth-generation (e.g., cefepime) have very broad spectrum. C. difficile is a key adverse effect to remember.

SBA questions often focus on choosing the appropriate generation for a specific infection (e.g., meningitis vs. skin infection). Another common theme is the management of penicillin allergy, particularly the risk of cross-reactivity with cephalosporins. Questions might also test knowledge of common adverse effects like C. difficile.