GARAMYCIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GARAMYCIN (GARAMYCIN).
Gentamicin is an aminoglycoside antibiotic that binds to the 30S ribosomal subunit, causing misreading of mRNA and inhibition of protein synthesis, leading to bacterial cell death.
| Metabolism | Gentamicin undergoes minimal hepatic metabolism; primarily excreted unchanged in urine via glomerular filtration. |
| Excretion | Primarily renal (glomerular filtration); >90% excreted unchanged in urine within 24 hours. Minimal biliary/fecal elimination (<2%). |
| Half-life | Terminal elimination half-life: 2-3 hours in adults with normal renal function; prolonged in renal impairment (up to 40-50 hours in anuria). |
| Protein binding | 10-30% bound; primarily to albumin. |
| Volume of Distribution | 0.2-0.3 L/kg (low); reflects primarily extracellular fluid distribution with minimal intracellular penetration. |
| Bioavailability | IM: ~100% (complete absorption); Oral: <1% (not absorbed); IV: 100%. |
| Onset of Action | IM: 30-60 min; IV: immediate (peak concentration at end of infusion). |
| Duration of Action | Approximately 8-12 hours; drug concentration-dependent bactericidal effect persists post-antibiotic effect (PAE) of 2-4 hours for susceptible organisms. |
| Action Class | Aminoglycosides |
| Brand Substitutes | Germenta 80mg Injection, Gmi 80mg Injection, Gentact Injection, Zoftagen 80mg Injection, Gentacore 80mg Injection |
Gentamicin 3-5 mg/kg/day IV or IM in 3 divided doses every 8 hours for serious infections; may use once-daily dosing (5 mg/kg IV every 24 hours) for certain indications.
| Dosage form | SOLUTION/DROPS |
| Renal impairment | CrCl >60 mL/min: usual dose. CrCl 40-60: 3 mg/kg/day divided q12h. CrCl 20-40: 3 mg/kg/day divided q24h. CrCl <20: 3 mg/kg loading dose then monitor levels and redose when trough <2 mcg/mL. Hemodialysis: 2-3 mg/kg post-dialysis. |
| Liver impairment | No specific dose adjustment recommended for hepatic impairment; use standard dosing. Monitor renal function closely as hepatic disease may affect renal elimination. |
| Pediatric use | Neonates <1 week: 2.5 mg/kg IV/IM every 12 hours. Infants 1-4 weeks: 2.5 mg/kg IV/IM every 8 hours. Children: 2-2.5 mg/kg IV/IM every 8 hours. For cystic fibrosis, higher doses may be needed. |
| Geriatric use | Start with lower initial dose (1-1.5 mg/kg) and adjust based on renal function; monitor trough and peak levels to avoid toxicity. Extended intervals (e.g., every 24-48 hours) may be appropriate based on CrCl. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for GARAMYCIN (GARAMYCIN).
| Breastfeeding | Gentamicin is excreted into human breast milk in small amounts. The milk-to-plasma ratio is approximately 0.2–0.4. Due to poor oral bioavailability, systemic absorption in the infant is unlikely. However, potential for alteration of infant gut flora and interference with infant's auditory/renal function. Caution is advised; consider discontinuing breastfeeding or discontinuing drug. |
| Teratogenic Risk | FDA Pregnancy Category D. Aminoglycosides cross the placenta. There is evidence of human fetal risk, but potential benefits may warrant use in pregnant women despite potential risks. First trimester: Risk of ototoxicity and nephrotoxicity in the fetus based on other aminoglycosides; however, specific data for GARAMYCIN are limited. Second and third trimesters: Potential for fetal auditory and renal toxicity; avoid use unless clearly needed. Associated with fetal ototoxicity (eighth cranial nerve damage) and nephrotoxicity, especially with prolonged or high-dose therapy. |
■ FDA Black Box Warning
Aminoglycosides are associated with nephrotoxicity and ototoxicity (vestibular and auditory). Risk increases with higher doses, prolonged use, renal impairment, and concomitant use of other ototoxic/nephrotoxic drugs. Monitoring renal function and drug levels is essential.
| Serious Effects |
["Hypersensitivity to gentamicin or other aminoglycosides","Severe renal impairment without availability for therapeutic drug monitoring","Previous aminoglycoside-induced ototoxicity or nephrotoxicity","Concurrent use with other nephrotoxic or ototoxic drugs (relative contraindication)"]
| Precautions | ["Nephrotoxicity: Monitor renal function; adjust dosing in renal impairment.","Ototoxicity: May cause irreversible bilateral hearing loss and vestibular damage; monitor audiovestibular function.","Neuromuscular blockade: Use with caution in patients with neuromuscular disorders (e.g., myasthenia gravis); may exacerbate weakness.","Fetal harm: Crosses placenta; avoid in pregnancy unless life-threatening infection.","Superinfection: Prolonged use may lead to overgrowth of resistant organisms."] |
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| Fetal Monitoring | Monitor maternal renal function (serum creatinine, BUN) and gentamicin trough/peak levels to avoid toxicity. Assess auditory function (audiometry) and vestibular function before and during therapy. Monitor fetal well-being via ultrasound for growth and amniotic fluid volume. Newborn hearing screening recommended after delivery. |
| Fertility Effects | No specific data in humans. Animal studies have not demonstrated impaired fertility. However, aminoglycosides may cause oxidative stress in testes; clinical significance unknown. Use with caution in patients attempting conception. |