GENTAK
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GENTAK (GENTAK).
Gentamicin is an aminoglycoside antibiotic that binds to the 30S ribosomal subunit of susceptible bacteria, causing misreading of mRNA and inhibiting protein synthesis, leading to bacterial cell death.
| Metabolism | Gentamicin is not significantly metabolized; it is excreted unchanged primarily by glomerular filtration in the kidneys. Approximately 30-100% of the dose is recovered in urine within 24 hours. |
| Excretion | Renal excretion of unchanged drug accounts for >90% of elimination; <5% biliary/fecal. |
| Half-life | 2–3 hours in adults with normal renal function; prolonged to 24–60 hours in severe renal impairment (CrCl <10 mL/min). |
| Protein binding | ~10–20% bound to albumin; negligible binding to other proteins. |
| Volume of Distribution | 0.2–0.3 L/kg, indicating primarily extracellular fluid distribution. |
| Bioavailability | IM: ~100%; oral: <1% due to poor absorption; ophthalmic/topical: negligible systemic absorption. |
| Onset of Action | IM: 30–60 minutes; IV: immediate; topical: 3–5 days for anti-inflammatory effect. |
| Duration of Action | IM/IV: 6–8 hours; topical: anti-inflammatory effect persists 1–2 weeks after 3-week q12h therapy. |
Gentamicin 3-5 mg/kg IV or IM once daily; alternatively, 1.5-2.5 mg/kg IV or IM every 8 hours.
| Dosage form | SOLUTION/DROPS |
| Renal impairment | GFR >60 mL/min: 3-5 mg/kg q24h. GFR 40-59: 3-5 mg/kg q36h. GFR 20-39: 3-5 mg/kg q48h. GFR <20: 3-5 mg/kg q72-96h, with TDM. Hemodialysis: 2-3 mg/kg after dialysis, with TDM. |
| Liver impairment | No specific Child-Pugh based adjustments; use standard dosing with TDM in severe hepatic impairment. |
| Pediatric use | Neonates <7 days: 4-5 mg/kg IV/IM q24h. Neonates 7-28 days: 4-5 mg/kg q24h. Infants/children: 2.5 mg/kg IV/IM q8h or 5-7.5 mg/kg q24h. TDM recommended. |
| Geriatric use | Initiate with 3-5 mg/kg IV/IM q24h (once-daily regimen) with TDM; monitor renal function and adjust interval based on CrCl. Avoid repeated dosing without serum level monitoring. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for GENTAK (GENTAK).
| Breastfeeding | Gentamicin is excreted into breast milk in low concentrations. The M/P ratio is not well established but estimated <0.5. Typical infant doses via breast milk are subtherapeutic (less than 1-2% of maternal weight-adjusted dose). However, aminoglycosides have poor oral bioavailability, so systemic effects in the infant are unlikely. Potential risks include alteration of infant gut flora and rare cases of diarrhea or allergic reaction. The manufacturer advises caution during breastfeeding, but it is generally considered compatible with breastfeeding by most guidelines. Monitor infant for signs of gastrointestinal disturbance. |
| Teratogenic Risk | Gentamicin is an aminoglycoside antibiotic classified as FDA Pregnancy Category D. There is evidence of fetal risk based on human data. In the first trimester, limited data suggest no major malformations, but aminoglycosides can cause ototoxicity and nephrotoxicity in the fetus. In the second and third trimesters, the drug crosses the placenta and may accumulate in fetal plasma and amniotic fluid, potentially causing irreversible bilateral congenital deafness (especially with high doses or prolonged use). The risk of ototoxicity is highest when administered near term. Overall, avoid use during pregnancy unless the benefit outweighs the risk, and consider alternative antibiotics. |
■ FDA Black Box Warning
Aminoglycosides, including gentamicin, are associated with nephrotoxicity and ototoxicity (both vestibular and auditory), which can occur even at therapeutic doses. Risk is increased with prolonged use, high doses, renal impairment, and concomitant use of other nephrotoxic or ototoxic drugs. Serial renal function and audiometric tests should be monitored. Avoid concurrent use of loop diuretics (e.g., ethacrynic acid).
| Serious Effects |
["Hypersensitivity to gentamicin, any aminoglycoside, or any component of the formulation.","Prior history of severe toxic reaction (e.g., ototoxicity, nephrotoxicity) to aminoglycosides.","Myasthenia gravis (relative contraindication due to risk of neuromuscular blockade)."]
| Precautions | ["Nephrotoxicity: Monitor renal function (e.g., serum creatinine, BUN, urine output); adjust dose in renal impairment.","Ototoxicity: May cause irreversible bilateral vestibular and cochlear damage; risk factors include high cumulative dose, renal impairment, concurrent ototoxic drugs (e.g., cisplatin, loop diuretics).","Neuromuscular blockade: Caution in patients with neuromuscular disorders (e.g., myasthenia gravis, botulism); may exacerbate weakness.","Pregnancy: Crosses placenta; potential for fetal harm (auditory or vestibular toxicity).","Hypersensitivity: Rash, fever, urticaria; anaphylaxis possible.","Superinfection: Prolonged use may result in overgrowth of non-susceptible organisms (e.g., fungi)."] |
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| Fetal Monitoring | Maternal: Renal function (serum creatinine, BUN, urinalysis) at baseline and periodically during therapy, especially in patients with renal impairment; serum gentamicin trough and peak concentrations for therapeutic drug monitoring (target peak: 6-10 mcg/mL, trough: <2 mcg/mL); audiometry if prolonged therapy or high cumulative dose; signs of nephrotoxicity or ototoxicity (tinnitus, hearing loss, dizziness). Fetal: No specific fetal monitoring required; however, in cases of prolonged or high-dose therapy, consider third-trimester fetal auditory screening after birth. Newborn: Hearing assessment (auditory brainstem response) if exposure occurred near delivery. |
| Fertility Effects | There is no evidence that gentamicin adversely affects human fertility. Animal studies have not shown impairment of fertility at clinically relevant doses. However, severe infections treated with gentamicin may indirectly impact fertility due to systemic illness. No specific recommendations regarding fertility are needed. In men, no significant effects on spermatogenesis have been reported. |