Tobramycin

Tobramycin is an aminoglycoside antibiotic used to treat serious infections caused by gram-negative bacteria. It exerts bactericidal activity by binding to the 30S subunit of bacterial ribosomes, causing misreading of mRNA and inhibition of protein synthesis. Tobramycin has a primarily aerobic, Gram-negative spectrum and is especially active against Pseudomonas aeruginosa; activity against many gram-positive organisms is limited.

Common indications include severe infections such as intra-abdominal, gynecological, skin and soft tissue, respiratory, and septicemia caused by susceptible organisms, often in combination with beta-lactam antibiotics to achieve synergistic effect. Inhaled tobramycin is routinely used for chronic Pseudomonas aeruginosa infections in cystic fibrosis patients, while ophthalmic forms (eye drops or ointment) treat bacterial conjunctivitis. Parenteral administration is the usual route for systemic infections; oral absorption is limited, so oral tobramycin is not generally effective for systemic infections.

Pharmacokinetics and administration considerations vary by route. Tobramycin is mainly renally excreted and distributes in extracellular fluids; dosing often requires adjustment in renal impairment. Therapeutic drug monitoring of trough levels is commonly used to minimize toxicity. Concentration-dependent bactericidal activity supports once-daily or extended-interval dosing in some settings.

Resistance can arise via aminoglycoside-modifying enzymes, efflux mechanisms, or 16S rRNA methylation; cross-resistance among aminoglycosides can occur but is not universal. Common adverse effects include nephrotoxicity and ototoxicity (cochlear and vestibular), with increased risk in prolonged therapy, high trough levels, preexisting kidney disease, or concurrent nephrotoxic drugs. Neuromuscular blockade and, rarely, allergic reactions may occur. Tobramycin is contraindicated in hypersensitivity to aminoglycosides; caution is advised in pregnancy and neuromuscular disease.