💊 Aminoglycosides

Aminoglycosides are a class of bactericidal antibiotics primarily effective against Gram-negative aerobic bacteria. They are often used in combination with beta-lactam antibiotics for synergistic effect against serious infections.

Aminoglycosides irreversibly bind to the 30S ribosomal subunit of susceptible bacteria. This binding interferes with the initiation of protein synthesis, causes misreading of mRNA, and leads to the production of non-functional proteins, ultimately resulting in bacterial cell death.

They are typically reserved for serious Gram-negative infections, including septicaemia, complicated urinary tract infections, and hospital-acquired pneumonia. They are also used in combination therapy for endocarditis and severe intra-abdominal infections. Topical formulations are used for eye and ear infections.

Known hypersensitivity is an absolute contraindication. They are contraindicated in patients with myasthenia gravis due to their neuromuscular blocking properties. Caution is required in patients with pre-existing renal impairment, hearing impairment, or those receiving other ototoxic or nephrotoxic drugs.

The most significant adverse effects are nephrotoxicity (reversible acute tubular necrosis) and ototoxicity (irreversible vestibular and cochlear damage, leading to hearing loss and vertigo). Other effects include neuromuscular blockade and allergic reactions.

Therapeutic drug monitoring (TDM) of plasma concentrations (peak and trough levels) is crucial to optimise efficacy and minimise toxicity. Renal function (urea, creatinine, eGFR) must be closely monitored before and during treatment. Audiometry may be considered in patients at high risk of ototoxicity or prolonged therapy.

Always check renal function before prescribing and ensure appropriate dose adjustment. Be aware of concomitant nephrotoxic (e.g., NSAIDs, ciclosporin) or ototoxic (e.g., loop diuretics, vancomycin) medications. Counsel patients on potential side effects like hearing changes or dizziness and to report them promptly. Emphasise the importance of blood tests.

Gentamicin is a commonly used aminoglycoside. They are bactericidal and concentration-dependent killers. Key toxicities are nephrotoxicity and ototoxicity, both irreversible. Therapeutic drug monitoring (TDM) is essential. Often given once daily to allow a drug-free period for renal recovery. Avoid in myasthenia gravis.

SBA questions frequently focus on the narrow therapeutic index of aminoglycosides, necessitating therapeutic drug monitoring. The key toxicities – nephrotoxicity and ototoxicity – and their irreversible nature are common themes. Questions might also test drug interactions with other nephrotoxic or ototoxic agents.