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. |
| Molecular Weight | 477.6 |
| 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 | Avoid: Associated with fetal ototoxicity and nephrotoxicity; use only for life-threatening infections with no safer alternative. |
| 2nd trimester | Avoid: Same risks as t1; potential for fetal harm. |
| 3rd trimester | Avoid: Risk of neonatal toxicity; caution if used near term. |
Clinical note
Comprehensive clinical and safety monograph for GARAMYCIN (GARAMYCIN).
| Placental transfer | Gentamicin crosses the placenta; fetal serum levels reach approximately 30-50% of maternal levels. |
| Breastfeeding | Gentamicin is excreted into breast milk in small amounts; however, absorption by the infant is limited. Caution is advised due to potential for gut flora alteration and risk of nephrotoxicity/ototoxicity in neonates. Monitor infant for signs of toxicity. |
■ 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 any aminoglycosideMyasthenia gravis (may exacerbate weakness)
| 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. |
| Food/Dietary | No significant food-drug interactions. However, avoid excessive intake of potassium-rich foods if used with potassium-sparing diuretics, as gentamicin may cause electrolyte disturbances. Maintain adequate hydration to reduce nephrotoxicity risk. |
Loading safety data…
| Lactation Rating |
| L2 (Probably Compatible) |
| 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. |
| 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. |
| Clinical Pearls | Garamycin (gentamicin) is an aminoglycoside antibiotic with concentration-dependent bactericidal activity. Monitor peak (target 5-10 µg/mL) and trough (<2 µg/mL) levels to optimize efficacy and minimize toxicity. Adjust dose based on renal function (CrCl) and consider extended-interval dosing (e.g., 5-7 mg/kg q24h) for improved efficacy and reduced nephrotoxicity. Avoid concurrent use of other nephrotoxic drugs (e.g., vancomycin, NSAIDs, contrast dye). Assess for ototoxicity (vestibular and cochlear) with serial audiometry in prolonged therapy. For synergy in enterococcal endocarditis, use with a cell-wall-active agent. |
| Patient Advice | Take this medication exactly as prescribed; do not skip doses or stop early even if you feel better. · This medication is given as an injection into a muscle or vein; it is not taken by mouth. · You may experience dizziness, hearing loss, or ringing in the ears; report these to your doctor immediately. · Drink plenty of fluids (unless instructed otherwise) to help prevent kidney problems. · Tell your doctor about all other medications you take, especially diuretics or other antibiotics. · Women who are pregnant or breastfeeding should discuss risks with their doctor before use. |