Gentamicin

# Gentamicin ## Overview - **Classification**: Aminoglycoside antibiotic - **Mechanism**: Inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, leading to a defective cell membrane and cell death. Bactericidal. ## Primary Indications 1. **Serious Gram-negative Infections** - Empiric or directed therapy for complicated UTIs, pneumonia, sepsis caused by *Pseudomonas aeruginosa*, Enterobacteriaceae. 2. **Synergistic Therapy** - Used with beta-lactams or glycopeptides for serious Gram-positive infections (e.g., Enterococcal endocarditis, Staphylococcal infections). 3. **Surgical Prophylaxis** - In specific high-risk procedures, often colorectal surgery. ## Adult Dosing ### Standard Dosing **Serious Gram-negative Infections (Traditional)** - **Dose**: **1-1.7 mg/kg** (ideal body weight for obese patients) - **Frequency**: Every **8 hours** - **Route**: Intravenous (IV) infusion over 30-60 min or Intramuscular (IM) - **Duration**: Typically 7-10 days, or as clinically indicated **Serious Gram-negative Infections (Extended-Interval / Once-Daily)** - **Dose**: **5-7 mg/kg** (ideal body weight) - **Frequency**: Every **24 hours** - **Route**: IV infusion over 30-60 min - **Considerations**: Preferred in many cases due to reduced nephrotoxicity risk and convenience; requires specific nomograms/monitoring. **Synergistic Therapy (e.g., Endocarditis)** - **Dose**: **1 mg/kg** - **Frequency**: Every **8 hours** - **Route**: IV or IM - **Considerations**: Used in combination with a cell wall-active agent (e.g., penicillin, vancomycin). ### Dose Adjustments - **Renal Impairment**: Requires significant dose reduction or interval extension based on creatinine clearance (CrCl). - CrCl **60-90 mL/min**: Traditional dosing, monitor levels. - CrCl **30-59 mL/min**: Interval extension (e.g., q12-24h) or dose reduction. - CrCl **<30 mL/min**: Further interval extension (e.g., q24-48h or longer) or lower doses; often dosed post-dialysis. - **Hepatic Impairment**: No specific dose adjustment needed, but monitor renal function as hepatorenal syndrome can occur. - **Elderly Patients**: Increased risk of nephrotoxicity and ototoxicity due to age-related decline in renal function. Use lower doses and/or extended intervals. Monitor renal function and drug levels closely. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: **2.5 mg/kg** - **Frequency**: Every **12-24 hours** (longer for premature infants or those < 7 days old) - **Maximum**: Typically **5 mg/kg/day** total. - **Special Notes**: Dosing interval depends on gestational age and postnatal age; monitor levels carefully due to variable renal function. ### Infants (1-12 months) - **Dose**: **2.5 mg/kg** - **Frequency**: Every **8 hours** - **Maximum**: **7.5 mg/kg/day**. ### Children (1-12 years) - **Dose**: **2-2.5 mg/kg** - **Frequency**: Every **8 hours** (Traditional) or **5-7 mg/kg** every **24 hours** (Extended-Interval) - **Maximum**: **7.5 mg/kg/day** or adult maximum daily dose, whichever is lower. ### Adolescents (13-18 years) - **Dose**: Follow adult dosing guidelines. **2-2.5 mg/kg** q8h (traditional) or **5-7 mg/kg** q24h (extended-interval). - **Maximum**: Adult doses. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to gentamicin or other aminoglycosides. - **Relative**: Pre-existing hearing loss, myasthenia gravis, parkinsonism (can worsen neuromuscular weakness). ### Common Adverse Effects - **Common (1-10%)**: - **Nephrotoxicity**: Reversible acute tubular necrosis (elevated SCr, decreased urine output). - **Ototoxicity**: Irreversible auditory (tinnitus, hearing loss) or vestibular (dizziness, vertigo, nystagmus) damage. - **Serious but Rare**: - Neuromuscular blockade: Respiratory depression, muscle weakness. - *Clostridioides difficile* infection (CDI). ### Key Drug Interactions - **Nephrotoxic Drugs**: NSAIDs, vancomycin, amphotericin B, cyclosporine, tacrolimus, loop diuretics. Increased risk of nephrotoxicity. Avoid concurrent use or monitor renal function very closely. - **Ototoxic Drugs**: Loop diuretics (e.g., furosemide), vancomycin, cisplatin. Increased risk of ototoxicity. - **Neuromuscular Blockers**: Succinylcholine, rocuronium. Potentiates neuromuscular blockade, leading to prolonged respiratory depression. Monitor respiratory status. ## Monitoring & Follow-up - **Before Treatment**: Baseline renal function (SCr, CrCl), electrolytes. Hearing assessment if pre-existing risk factors. - **During Treatment**: - **Renal Function**: Serum creatinine (SCr) daily or every other day. - **Drug Levels**: Therapeutic drug monitoring (TDM) is essential. - **Trough levels**: Draw just prior to the 3rd or 4th dose (for q8h dosing); should be undetectable for q24h. - **Peak levels**: Draw 30-60 minutes after end of infusion for q8h dosing. - **Clinical Signs**: Monitor for signs of ototoxicity (tinnitus, hearing changes, vertigo) and nephrotoxicity (decreased urine output, edema). - **Infection Response**: Fever resolution, improved WBC count, negative cultures. ## Clinical Pearls - 💡 **Tip 1**: Extended-interval (once-daily) dosing is often preferred for serious Gram-negative infections due to comparable efficacy, reduced nephrotoxicity, and improved patient adherence. - 💡 **Tip 2**: Therapeutic drug monitoring is crucial for safe and effective gentamicin use due to its narrow therapeutic index and significant inter-patient variability. - 💡 **Tip 3**: Maintain adequate hydration to minimize the risk of nephrotoxicity. - 💡 **Tip 4**: Counsel patients on symptoms of ototoxicity (ringing in ears, hearing changes, dizziness) and to report them immediately. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.