TOBRAMYCIN 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; binds to 30S ribosomal subunit, causing misreading of mRNA and inhibiting bacterial protein synthesis.
| Metabolism | Not metabolized; eliminated renally by glomerular filtration (90% unchanged in urine). |
| Excretion | Primarily renal (glomerular filtration) with 90-95% excreted unchanged in urine within 24 hours; biliary/fecal <1%. |
| Half-life | Terminal elimination half-life is 2-3 hours in patients with normal renal function; extends to 24-100 hours in severe renal impairment (CrCl <10 mL/min), requiring dose adjustment. |
| Protein binding | <5% bound to serum proteins (primarily albumin). |
| Volume of Distribution | 0.2-0.3 L/kg, approximating extracellular fluid volume; increased in edema, ascites, or burn patients. |
| Bioavailability | Intravenous: 100%; intramuscular: >90%; inhaled: <10% systemic (local action); oral: <1% (not used systemically). |
| Onset of Action | Intravenous: within 30-60 minutes after infusion; intramuscular: 30-60 minutes; inhaled: within 15-30 minutes (peak sputum levels). |
| Duration of Action | Serum concentrations above MIC persist for 6-8 hours after IV/IM; dosing interval typically every 8 hours. Inhaled: bronchoalveolar levels maintained for 12-24 hours. |
| Molecular Weight | 467.5 |
Adults: Tobramycin 3-5 mg/kg/day IV divided every 8 hours, or 5-7 mg/kg/day IV once daily. For inhalation: 300 mg nebulized twice daily.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 30-59 mL/min: 3-5 mg/kg IV every 12-24 hours. CrCl 10-29 mL/min: 3-5 mg/kg IV every 24-48 hours. CrCl <10 mL/min: 3-5 mg/kg IV every 48-72 hours. Hemodialysis: 1.5-2 mg/kg after dialysis. |
| Liver impairment | No specific adjustment required. Monitor serum levels if severe hepatic impairment. |
| Pediatric use | Infants and children: 2.5 mg/kg IV/IM every 8 hours (total 7.5 mg/kg/day) or 4-7 mg/kg IV once daily; adjust per therapeutic drug monitoring. |
| Geriatric use | Initial dose based on ideal body weight and renal function. Reduce dose and/or extend interval due to age-related decreased GFR; monitor serum levels. |
| 1st trimester | Aminoglycosides cross the placenta. Avoid during first trimester due to potential for ototoxicity and nephrotoxicity; use only if clearly needed and no safer alternative. |
| 2nd trimester | Use with caution during second trimester; maternal benefit may outweigh fetal risk. Monitor drug levels and renal function. |
| 3rd trimester | Use with caution during third trimester; risk of fetal ototoxicity (8th cranial nerve damage) and nephrotoxicity. Avoid prolonged or high-dose therapy. |
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; fetal serum levels reach approximately 15-50% of maternal levels. |
■ FDA Black Box Warning
Boxed warning for neurotoxicity (including ototoxicity and nephrotoxicity) and neuromuscular blockade. Risk of fetal harm if used in pregnancy.
| Common Effects | Nephrotoxicity |
| Serious Effects |
Hypersensitivity to tobramycin or any aminoglycosideMyasthenia gravis (risk of neuromuscular blockade)
| Precautions | Monitor renal function, audiometry, and serum trough/peak levels. Risk of ototoxicity (irreversible), nephrotoxicity, and neuromuscular blockade. Avoid concurrent use of other nephrotoxic/ototoxic drugs. Use with caution in renal impairment, myasthenia gravis, or parkinsonism. |
| Food/Dietary | No significant food interactions. Avoid alcohol as it may increase dizziness. |
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| Breastfeeding |
| Tobramycin is poorly absorbed orally; minimal transfer into breastmilk. Considered compatible with breastfeeding by the AAP. Monitor infant for diarrhea, rash, or changes in stool. |
| Lactation Rating | L1 (Safe) |
| Teratogenic Risk | Aminoglycosides cross the placenta. First trimester: Limited data, but no consistent evidence of major malformations. Second/third trimester: Risk of fetal ototoxicity (cranial nerve VIII damage) and nephrotoxicity, especially with prolonged or high-dose exposure. Theoretical risk of neuromuscular blockade. Use only for strong maternal indications. |
| Fetal Monitoring | Monitor maternal renal function (serum creatinine, BUN) and serum drug levels (trough and peak) to avoid toxicity. Assess fetal well-being with ultrasound for growth, and consider auditory screening (neonatal otoacoustic emissions) if prolonged exposure. Check for signs of fetal distress if used for maternal sepsis. |
| Fertility Effects | No known direct effects on fertility. Animal studies show no impairment. In males, aminoglycosides may rarely cause reversible infertility due to effects on sperm motility; clinical significance unclear. |
| Clinical Pearls | Monitor peak (15-20 mg/L) and trough (<2 mg/L) levels for efficacy and toxicity. Adjust dose in renal impairment (CrCl <60 mL/min). Avoid concurrent use with neurotoxic or nephrotoxic drugs. Observe for ototoxicity (vertigo, tinnitus) especially in cystic fibrosis patients receiving chronic therapy. For inhalation, pre-treat with bronchodilator if patient has bronchospasm. |
| Patient Advice | Take exactly as prescribed; do not skip doses even if feeling better. · Drink plenty of fluids to reduce kidney irritation. · Report any hearing loss, ringing in ears, dizziness, or difficulty urinating. · For inhalation, rinse mouth after use to prevent thrush. · Avoid taking other medications without doctor approval, especially diuretics or other antibiotics. |