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# Tobramycin ## Overview Tobramycin is an aminoglycoside antibiotic that inhibits bacterial protein synthesis, leading to bacterial cell death. It is bactericidal and has poor oral absorption, necessitating parenteral administration. ## Primary Indications * **Severe, life-threatening infections** caused by susceptible Gram-negative bacteria, including *Pseudomonas aeruginosa*. * **Urinary tract infections** (complicated and uncomplicated). * **Bacteremia and septicemia**. * **Lower respiratory tract infections** (e.g., hospital-acquired pneumonia). * **Intra-abdominal infections**. * **Bone and joint infections**. * **Skin and soft tissue infections**. * **Endocarditis** (in combination with other agents). * **Ophthalmic infections** (as tobramycin ophthalmic solution/ointment). ## Adult Dosing * **Complicated UTIs, serious infections:** 3-5 mg/kg/day IV or IM divided into 3 equal doses every 8 hours. * **Less severe infections:** 2 mg/kg/day IV or IM divided into 3 equal doses every 8 hours. * **Cystic Fibrosis exacerbations:** Dosing may vary based on pulmonary function and local protocols, often higher doses or extended intervals. * **Ophthalmic:** * Solution: 1-2 drops instilled into the conjunctival sac every 4 hours. For severe infections, increase frequency to every 30-60 minutes. * Ointment: Apply a small amount (e.g., 1/2 inch ribbon) into the conjunctival sac 2-3 times daily. ***Maximum dose:** Generally not to exceed 5 mg/kg/day for serious infections. ## Pediatric Dosing * **Neonates (< 1 week, premature):** 4 mg/kg/dose IV or IM every 12-24 hours. * **Neonates (1 week to < 1 month):** 4 mg/kg/dose IV or IM every 8-12 hours. * **Infants and Children (> 1 month):** * **Serious infections:** 2-2.5 mg/kg/dose IV or IM every 8 hours. * **Less severe infections:** 1.5-2 mg/kg/dose IV or IM every 8 hours. * **Ophthalmic:** * Solution: 1-2 drops instilled into the conjunctival sac every 4 hours. For severe infections, increase frequency to every 30-60 minutes. * Ointment: Apply a small amount (e.g., 1/2 inch ribbon) into the conjunctival sac 2-3 times daily. ## Dose Adjustments * **Renal Impairment:** Dose must be adjusted based on creatinine clearance (CrCl). * **Mild to moderate impairment:** Increase dosing interval. * **Severe impairment:** Significantly reduce dose and/or increase dosing interval. * **Alternative dosing strategies for renal impairment include:** * Administering a standard dose less frequently (e.g., every 24-48 hours). * Administering a reduced dose at the standard interval. * *Consult renal dosing guidelines or a pharmacist for precise calculations.* * **Hepatic Impairment:** Generally not considered significant. ## Contraindications * Hypersensitivity to tobramycin or other aminoglycosides. * Hypersensitivity to any component of the formulation. * Congenital neuromuscular neuromuscular transmission disorders (e.g., myasthenia gravis). ## Adverse Effects * **Ototoxicity:** * Auditory: Tinnitus, hearing loss (irreversible in some cases). * Vestibular: Dizziness, vertigo, ataxia. * **Nephrotoxicity:** Azotemia (elevated BUN and creatinine), oliguria, renal failure. Usually reversible. * **Neuromuscular blockade:** Respiratory depression, paralysis. * **Gastrointestinal:** Nausea, vomiting, diarrhea, stomatitis. * **Hematologic:** Eosinophilia, anemia, leukopenia, thrombocytopenia. * **Hypersensitivity reactions:** Rash, urticaria, pruritus, anaphylaxis. * **Local reactions:** Pain, tenderness, inflammation at injection site. ## Key Drug Interactions * **Penicillins (e.g., piperacillin, ticarcillin):** In vitro inactivation of tobramycin in the same IV solution; administer separately. Synergistic effect possible with certain *Pseudomonas* infections. * **Cephalosporins:** Increased risk of nephrotoxicity. * **Diuretics (e.g., furosemide, ethacrynic acid):** Increased risk of ototoxicity and nephrotoxicity. * **Neuromuscular blockers (e.g., succinylcholine, anesthetics):** Potentiated neuromuscular blockade, leading to respiratory depression. * **Vancomycin, cyclosporine, amphotericin B:** Increased risk of nephrotoxicity. ## Monitoring * **Renal function:** Baseline and periodic assessment of serum creatinine, BUN, and CrCl. * **Auditory and Vestibular function:** Assess for signs and symptoms of ototoxicity, especially with prolonged therapy or risk factors. * **Serum tobramycin concentrations:** Trough and peak levels are critical for optimizing efficacy and minimizing toxicity. * **Goal Trough:** Typically < 2 mcg/mL (may vary based on indication and susceptibility). * **Goal Peak:** Varies, generally based on susceptibility testing and desired AUC/MIC ratio. Common targets are 6-10 mcg/mL for standard dosing, potentially higher for extended-interval dosing. * *Timing of levels is crucial and depends on the dosing interval (e.g., trough drawn just before the next dose, peak 30-60 minutes after IV infusion completion).* * **Electrolytes:** Monitor for hypomagnesemia, hypocalcemia, hypokalemia. * **I/O balance:** Monitor for adequate urine output. ## Clinical Pearls * Aminoglycosides undergo glomerular filtration, so dose adjustments are essential in renal impairment. * Concurrent use with nephrotoxic agents increases the risk of kidney damage. * Concurrent use with neurotoxic agents increases the risk of ototoxicity. * Extended-interval dosing (e.g., once daily) may be preferred in adults with normal renal function as it potentially reduces toxicity while maintaining efficacy, but requires careful monitoring of peak and trough levels. * Trough concentrations significantly elevated suggest accumulation and potential for toxicity; dose reduction or lengthening of interval may be needed. * Vomiting or diarrhea can lead to increased fluid loss and potential dehydration, affecting renal function and drug levels. * Hydration is important. *** **Disclaimer:** This information is intended for clinical professionals. Always refer to the most current prescribing information approved by the regulatory agency, product labeling, and institutional guidelines for complete and accurate drug information. This summary is not a substitute for professional judgment.