GENTAMICIN SULFATE
Clinical safety rating: avoid
Other nephrotoxic or ototoxic drugs increase risk of toxicity Monitor peak and trough levels to minimize risk of nephrotoxicity and ototoxicity.
Aminoglycoside antibiotic that binds to the 30S ribosomal subunit, causing misreading of mRNA and inhibiting protein synthesis. Also disrupts bacterial cell membrane integrity.
| Metabolism | Minimally metabolized; primarily excreted unchanged by glomerular filtration. No significant hepatic metabolism. |
| Excretion | Renal excretion of unchanged drug accounts for >90% of elimination; biliary/fecal <2%. |
| Half-life | Terminal elimination half-life: 2-4 hours in patients with normal renal function; prolonged to 24-72 hours in renal impairment. |
| Protein binding | <30% bound to albumin; primarily free in circulation. |
| Volume of Distribution | 0.2-0.3 L/kg; approximates extracellular fluid volume; increased in edematous states. |
| Bioavailability | IM: ~100%; topical/ophthalmic: minimal systemic absorption (<0.3%); oral: negligible (<1%). |
| Onset of Action | IM: 30-60 minutes; IV: within 30 minutes; topical/ophthalmic: variable, clinical effect within 24-48 hours. |
| Duration of Action | Approximately 6-12 hours with normal renal function; prolonged in renal impairment; monitoring of trough levels recommended. |
| Molecular Weight | 477.6 |
1-2 mg/kg IV every 8 hours or 3-5 mg/kg IV every 24 hours for extended-interval dosing; typical duration 7-10 days.
| Dosage form | INJECTABLE |
| Renal impairment | GFR 20-50 mL/min: 1-2 mg/kg IV every 12 hours; GFR 10-19 mL/min: 1-2 mg/kg IV every 24 hours; GFR <10 mL/min: 1-2 mg/kg IV every 48-72 hours; monitor serum levels. |
| Liver impairment | No dose adjustment required for Child-Pugh Class A, B, or C; monitor renal function. |
| Pediatric use | Neonates: 2.5-5 mg/kg IV every 12-24 hours based on gestational age and postnatal age; Children: 2-2.5 mg/kg IV every 8 hours; extended-interval dosing: 4-7 mg/kg IV every 24 hours. |
| Geriatric use | Reduced initial dose (1-2 mg/kg IV) based on renal function; monitor serum creatinine and drug trough levels; increased risk of nephrotoxicity and ototoxicity. |
| 1st trimester | Associated with irreversible bilateral vestibular damage and hearing loss; avoid unless strongly indicated. Crosses placenta; risk of fetal ototoxicity. |
| 2nd trimester | Use only for life-threatening infections; potential fetal ototoxicity and nephrotoxicity. Monitor drug levels. |
| 3rd trimester | Use with caution; risk of fetal ototoxicity. Prolonged use may cause eighth cranial nerve damage in neonate. |
Clinical note
Other nephrotoxic or ototoxic drugs increase risk of toxicity Monitor peak and trough levels to minimize risk of nephrotoxicity and ototoxicity.
| FDA category | Positive |
| Placental transfer | Crosses placenta; achieves fetal serum concentrations 15-50% of maternal levels. Accumulates in fetal kidneys, inner ear, and amniotic fluid. |
■ FDA Black Box Warning
Potential for nephrotoxicity (especially in patients with pre-existing renal impairment or those receiving other nephrotoxic drugs) and ototoxicity (vestibular and cochlear, which may be irreversible). Risk is increased with higher doses, prolonged therapy, or in elderly patients. Also, neuromuscular blockade and respiratory paralysis have been reported, particularly with concurrent use of anesthetics or neuromuscular blocking agents. Use during pregnancy may cause fetal harm.
| Common Effects | Nephrotoxicity |
| Serious Effects |
Hypersensitivity to gentamicin or any aminoglycosidePrevious history of ototoxicity with aminoglycosidesMyasthenia gravis (may exacerbate weakness)
| Precautions | Monitor renal function (serum creatinine, BUN, urine output) and drug levels (peak and trough) to avoid toxicity., Assess hearing (audiometry) before and during therapy; discontinue if tinnitus or vertigo occurs., Use with caution in elderly, dehydrated, or patients with renal impairment., Avoid concurrent use of other nephrotoxic or ototoxic drugs (e.g., loop diuretics, vancomycin, cisplatin)., May exacerbate muscle weakness in patients with myasthenia gravis or other neuromuscular disorders., Prolonged use may result in overgrowth of non-susceptible organisms. |
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| Breastfeeding |
| Excreted into breast milk in low concentrations; unlikely to cause adverse effects in infant due to poor oral bioavailability. However, use caution in neonates with gastrointestinal disorders or renal impairment. Monitor infant for signs of diarrhea, candidiasis, or hypersensitivity. |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Aminoglycosides cross the placenta. First trimester: No clear evidence of major malformations, but risk cannot be excluded. Second/third trimester: Potential for fetal ototoxicity (8th cranial nerve damage) and nephrotoxicity, especially with prolonged or high-dose exposure; use only if clearly needed. |
| Fetal Monitoring | Monitor maternal renal function (serum creatinine, BUN), gentamicin trough and peak levels, and auditory function. Fetal monitoring includes ultrasound for growth and amniotic fluid volume; consider newborn hearing screen after delivery if exposure occurred in 2nd/3rd trimester. |
| Fertility Effects | No direct evidence of adverse effects on fertility in humans. Animal studies show no significant reproductive toxicity at therapeutic doses. However, systemic illness requiring gentamicin may indirectly affect fertility. |
| Food/Dietary | No specific food restrictions. Maintain adequate hydration. Avoid excessive intake of caffeine or alcohol as they may worsen dehydration or kidney function. Use caution with potassium-rich foods if renal impairment exists. |
| Clinical Pearls | Gentamicin is an aminoglycoside antibiotic with concentration-dependent bactericidal activity. Monitor peak (target: 4-10 mcg/mL for most infections, 10-12 mcg/mL for severe infections like pneumonia) and trough (target: <2 mcg/mL, ideally <1 mcg/mL) levels to reduce nephrotoxicity and ototoxicity. Adjust dosing based on renal function (CrCl). Avoid concomitant use with other nephrotoxic agents (e.g., amphotericin B, cyclosporine, loop diuretics). Extended-interval dosing (once daily) is preferred for most indications except endocarditis and burns. Rapid infusion over 30-60 minutes is recommended. Consider therapeutic drug monitoring for all patients, especially those with renal impairment, obesity, critical illness, or prolonged therapy (>5 days). Ototoxicity may be irreversible and can occur even after discontinuation. Assess for vestibular toxicity: perform Romberg test and inquire about dizziness or imbalance. For gram-negative meningitis, intrathecal or intraventricular administration may be required due to poor CSF penetration. Synergistic with beta-lactams against Pseudomonas aeruginosa and enterococci (for enterococcal endocarditis, use with ampicillin or vancomycin). |
| Patient Advice | Take this medication exactly as prescribed; do not skip doses or stop early. · Drink plenty of water to help prevent kidney damage. · Report any hearing loss, ringing in the ears, dizziness, or difficulty urinating immediately. · This drug may cause nerve damage; tell your doctor if you experience numbness, tingling, or muscle twitching. · Avoid taking other medications, including over-the-counter drugs, without consulting your doctor. · Inform all healthcare providers that you are taking gentamicin. · If you are pregnant, think you may be pregnant, or are breastfeeding, tell your doctor. |