Makindo Medical Notes

📖 About

• Gentamicin is a potent, broad-spectrum aminoglycoside antibiotic that inhibits bacterial protein synthesis.
• Always check the BNF or equivalent guidelines for up-to-date prescribing advice.

⚙️ Mode of Action

• Binds to the 30S ribosomal subunit (some aminoglycosides also bind 50S).
• Blocks translocation of peptidyl-tRNA from the A-site → P-site.
• Causes misreading of mRNA, preventing synthesis of functional bacterial proteins.
• Bactericidal against aerobic Gram-negative bacilli; requires oxygen for uptake (so ineffective against anaerobes).

🩺 Indications

• Severe Gram-negative infections (e.g., sepsis, intra-abdominal sepsis, pyelonephritis).
• Synergy with β-lactams in streptococcal/enterococcal endocarditis.
• Staphylococcal infections (with other agents).
• Occasionally used as a single-dose prophylaxis (e.g., around catheter changes) depending on local policy.

🚫 Contraindications & Cautions

• Renal impairment: dose adjustment and frequent monitoring required (risk of accumulation).
• Myasthenia gravis: risk of neuromuscular blockade.
• Pregnancy: crosses placenta → risk of fetal ototoxicity.

• Catheter change prophylaxis: 80–160 mg IV/IM pre-procedure.
• Uncomplicated UTI: occasionally 3–5 mg/kg IV/IM single dose, if local resistance patterns support.
• Monitor renal function in higher-risk patients (elderly, CKD).
• Avoid if pre-existing vestibular/auditory impairment.

🧪 Monitoring

• Serum levels:
  • Once-daily: random level 6–14 hrs post-dose → nomogram.
  • Multiple-daily: trough (before dose), peak (30 mins post-infusion).
• Renal function: U&E, creatinine baseline and during therapy.
• Ototoxicity: ask about tinnitus/balance; consider audiometry if prolonged therapy.

⚠️ Side Effects

• Ototoxicity (auditory and vestibular damage; may be irreversible).
• Nephrotoxicity (proximal tubular damage; often reversible if detected early).
• Neuromuscular blockade (risk in Myasthenia Gravis or with rapid IV bolus).

👥 Other Aminoglycosides

• Streptomycin: used in TB treatment regimens.
• Tobramycin, Kanamycin: similar to gentamicin, with specific uses.
• Neomycin: oral use pre-GI surgery (reduces colonic flora).

💊 Dosing – Gentamicin (always follow local policy & check BNF/datasheet)

Regimen	Details
📌 Once-daily / Extended-interval dosing	• 5–7 mg/kg IV or IM once daily (use actual or adjusted body weight) • Maximises bactericidal activity and may reduce nephrotoxicity • Levels: Take 6–14 h post-dose → plot on nomogram (e.g., Hartford, Birmingham) to adjust interval
📌 Conventional / Multiple-daily dosing	• 1–2 mg/kg every 8 h (q8h) • Peak levels: 5–10 mg/L (serious infection), 3–5 mg/L (synergy e.g., endocarditis) • Trough level: <1 mg/L (toxicity risk ↑ if >2 mg/L)
💉 Single-dose use	• May be used for catheter changes or uncomplicated UTIs • Always follow local antimicrobial guidance