Tobramycin

Tobramycin is an aminoglycoside antibiotic derived from Streptomyces tenebrarius that is used to treat various types of bacterial infections, particularly Gram-negative infections. It is especially effective against species of Pseudomonas.[8]

It was patented in 1965, and approved for medical use in 1974.[9] It is on the World Health Organization's List of Essential Medicines.[10] In 2023, it was the 298th most commonly prescribed medication in the United States, with more than 400,000 prescriptions.[11][12]

Medical uses

Tobramycin does not pass the gastro-intestinal tract, so for systemic use it can only be given intravenously or by injection into a muscle. Eye drops and ointments (tobramycin only, Tobrex, or combined with dexamethasone, sold as Tobradex) and nebulised formulations both have low systemic absorption. The formulation for injection is branded Nebcin. The nebulised formulation (brand name Tobi) is indicated in the treatment of exacerbations of chronic infection with Pseudomonas aeruginosa in people diagnosed with cystic fibrosis.[13][14]

Tobramycin eye drops (with or without dexamethasone) are indicated in the treatment of superficial infections of the eye, such as bacterial conjunctivitis.[15][16][17][18]

Tobramycin, in its injectable form, is also indicated for various severe or life-threatening infections caused by susceptible strains: sepsis, meningitis, lower respiratory tract infections, intra-abdominal infections, skin infections, bone infections, and skin structure infections, complicated and recurrent urinary tract infections.[19][5]

Contraindications

Tobramycin is contraindicated in people with hypersensitivity against aminoglycoside antibiotics.[21] The Infusion is also contraindicated in people with myasthenia gravis.[7]

Side effects

Like other aminoglycosides, a major side effect for tobramycin is ototoxicity or a loss of equilibrioception, or both in genetically susceptible individuals.[22] Other side effects include nephrotoxicity, neuromuscular toxicity, and hypersensitivity reactions.[23] Nephrotoxicity can be particularly worrisome when multiple doses accumulate over the course of a treatment[24] or when the kidney concentrates urine by increasing tubular reabsorption during sleep. Adequate hydration may help prevent excess nephrotoxicity and subsequent loss of renal function.[25] For these reasons parenteral tobramycin needs to be carefully dosed by body weight, and its serum concentration monitored. Tobramycin is thus said to be a drug with a narrow therapeutic index.

Interactions

Muscle relaxants and diethylether can add to the neuromuscular blocking effects of tobramycin.[7]

Methoxyflurane, when used as an inhalational anesthetic, can aggravate the nephrotoxic effects of injected tobramycin. Likewise, combining injected tobramycin with other nephrotoxic or ototoxic drugs can lead to more adverse effects; examples include amphotericin B, ciclosporin, cisplatin, vancomycin, and the diuretic furosemide. Other diuretics can also increase the risk for side effects because they raise tobramycin concentrations in the body fluids.[7]

Combining tobramycin with beta-lactam antibiotics can be desirable because of their synergistic effects. However, when they are given through the same drip, as well as in people with reduced kidney function, they can react with each other to form antibiotically inactive amides.[7]

Pharmacology

Society and culture

Tobramycin was patented in 1965, and approved for medical use in 1974.[9] Tobramycin is on the World Health Organization's List of Essential Medicines.[10] In 2023, tobramycin was the 298th most commonly prescribed medication in the United States, with more than 400,000 prescriptions.[11][12]

Tobrex eye drops are a 0.3% tobramycin sterile ophthalmic solution produced by Alcon Pharmaceuticals. Benzalkonium chloride 0.01% is added to Tobrex as a preservative.

Further reading