GENTAMICIN
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.
Binds to the 30S ribosomal subunit, causing misreading of mRNA and inhibition of protein synthesis; bactericidal against gram-negative aerobes.
| Metabolism | Gentamicin is an aminoglycoside antibiotic that is not metabolized in the body. It is excreted unchanged in the urine via glomerular filtration. No CYP450 enzymes are involved. No active metabolites. |
| Excretion | Primarily renal (glomerular filtration): 90-95% unchanged in urine over 24 hours; biliary/fecal: <2%. |
| Half-life | 2-3 hours in adults with normal renal function; prolonged to 24-48 hours in anuria; adjust dosing based on renal function. |
| Protein binding | <30% bound, primarily to albumin; minimal binding. |
| Volume of Distribution | 0.2-0.3 L/kg (central compartment); distributes poorly into fat, minimal CNS penetration. |
| Bioavailability | IM: ~100%; topical: negligible systemic absorption unless damaged skin. |
| Onset of Action | IV: 30-60 minutes; IM: 30-90 minutes; topical: not applicable for systemic effects. |
| Duration of Action | 6-8 hours after IV/IM in normal renal function; prolonged in renal impairment; monitor peak/trough levels. |
| Molecular Weight | 477.6 |
5-7 mg/kg/day IV or IM in divided doses every 8 hours; for serious infections, up to 5 mg/kg/day IV in 3 divided doses.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 30-59 mL/min: 3-4 mg/kg/day every 12 hours; CrCl 10-29 mL/min: 2-4 mg/kg/day every 24 hours; CrCl <10 mL/min: 1-2 mg/kg/day every 48-72 hours. |
| Liver impairment | No dose adjustment required based on Child-Pugh score; however, monitor renal function as hepatorenal syndrome may occur. |
| Pediatric use | Neonates: 2.5 mg/kg IV/IM every 12-24 hours depending on gestational age; Infants and children: 2.5 mg/kg/dose every 8 hours. |
| Geriatric use | Start at lower end of dosing range (3 mg/kg/day) and adjust based on renal function; monitor creatinine clearance and drug levels. |
| 1st trimester | Avoid unless no safer alternative; risk of ototoxicity and nephrotoxicity not established but potential harm; use only for life-threatening infections. |
| 2nd trimester | Use only if clearly needed; monitor serum levels due to altered pharmacokinetics; potential for fetal ototoxicity. |
| 3rd trimester | Risk of fetal ototoxicity and nephrotoxicity; avoid unless essential; consider alternative agents. |
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 the placenta achieving fetal serum concentrations 30-50% of maternal levels; documented transfer in multiple studies. |
| Breastfeeding |
■ FDA Black Box Warning
Boxed warnings: (1) Neurotoxicity (ototoxicity - vestibular and auditory) and nephrotoxicity risk; (2) Neuromuscular blockade and respiratory paralysis risk, especially with anesthetics or neuromuscular blocking agents; (3) Avoid concurrent or sequential use with other nephrotoxic/ototoxic drugs; (4) Monitor renal function and drug levels.
| Common Effects | Nephrotoxicity |
| Serious Effects |
Hypersensitivity to gentamicin or other aminoglycosidesMyasthenia gravis (may exacerbate muscle weakness)Previous severe aminoglycoside toxicity
| Precautions | Other nephrotoxic or ototoxic drugs increase risk of toxicity Monitor peak and trough levels to minimize risk of nephrotoxicity and ototoxicity. |
| Food/Dietary | No significant food interactions; however, avoid excessive salt intake if edema is a concern, and maintain consistent hydration. |
Loading safety data…
| Excreted into breast milk in low concentrations; poor oral bioavailability in infants minimizes systemic effects; however, monitor for diarrhea, candidiasis, and possible alteration of infant gut flora; use with caution in breastfeeding. |
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | Gentamicin is an aminoglycoside antibiotic classified as FDA Pregnancy Category D. In the first trimester, there is no strong evidence of major congenital malformations, but risk cannot be excluded. Second and third trimester exposure carries a risk of fetal ototoxicity (eighth cranial nerve damage) and nephrotoxicity, although absolute risk is low. Use only if clearly needed and if safer alternatives are unavailable. |
| Fetal Monitoring | Monitor maternal serum gentamicin trough and peak levels for efficacy and toxicity, as pregnancy alters pharmacokinetics. Assess renal function (serum creatinine, BUN, urine output) and hearing by audiometry in the mother if prolonged therapy. For the fetus, consider antenatal fetal surveillance including nonstress testing or biophysical profile if concerned about placental function or fetal growth restriction. |
| Fertility Effects | No significant evidence of adverse effects on fertility or reproductive function. Gentamicin does not impair sperm production or oocyte development in standard animal models. No human data suggesting negative impact on fertility. |
| Clinical Pearls | Monitor serum trough concentrations to avoid nephrotoxicity; goal trough <1-2 mcg/mL. Adjust dose based on renal function using Cockcroft-Gault equation. Synergistic with beta-lactams for enterococcal endocarditis. Avoid in pregnancy (risk of fetal ototoxicity). Consider once-daily dosing for most indications except endocarditis and pregnancy. Check for vestibular toxicity if patient reports dizziness. |
| Patient Advice | Take exactly as prescribed; do not skip doses. · Report any hearing loss, dizziness, or ringing in ears immediately. · Maintain adequate hydration unless instructed otherwise. · Notify your doctor if you experience decreased urine output or swelling. · This medication may cause diarrhea; contact your doctor if it becomes severe or contains blood. · Avoid taking other medications without consulting your doctor, especially those that can affect kidneys. |