Monitoring drug frequency and dosing are essential in tobramycin administration to decrease the chances of toxic side effects. Researchers have observed that a longer dosing interval may reduce the risk of ototoxicity and nephrotoxicity.[3] The dosing and frequency of administration require adjustment based on the patient’s renal function because the medication is retained longer in patients with renal abnormalities or renal failure.[15] The drug is excreted mainly by the kidneys, so it is essential to monitor renal function.[18] The serum half-life of tobramycin is about 2 hours in an adult and prolonged in neonates to about 4.5 to 8.7 hours.[19] Tobramycin can cross the placenta, concentrating in the kidney and urine of the fetus.[19] The theory is that tobramycin could potentially cause nephrotoxic events in the fetus, but this requires further investigation.[20]

A few serious toxicities that could happen with tobramycin include ototoxicity, nephrotoxicity, and neurotoxicity. These adverse reactions put limitations on the use of this class of broad-spectrum bactericidal antibiotics.

Ototoxicity

Ototoxicity occurs from the loss of hair cells in the inner ear.[21] The damage to cranial nerve VIII (vestibulocochlear nerve) could cause hearing or balance dysfunctions.[22] Once-daily administration of tobramycin is thought to help reduce the risk of ototoxicity.[3] This adverse effect is often irreversible.

Nephrotoxicity

Nephrotoxicity, unlike the ototoxicity, is a reversible adverse reaction.[22] In a double-blind study completed at Johns Hopkins University School of Medicine, researchers noted that the aminoglycoside-induced ototoxicity and nephrotoxicity occurred independently of each other.[22] Similar to preventing ototoxicity, nephrotoxicity is avoidable by longer dosing intervals.[3] Tobramycin can cause both direct nephrotoxicity, which is dose-related, as well as a hypersensitivity reaction.[23] Tobramycin activates the renin-angiotensin-aldosterone system and causes permanent vasoconstriction in the kidneys, causing an oliguric state with minimal urine output.[23] The toxic changes caused by tobramycin are observable in the proximal tubule.[23] Vacuolation and myeloid bodies in the tubular epithelial cell lysosomes are present under electron microscopy with the usage of the medication.[23] Granular casts, microscopic hematuria, and proteinuria are also often present.[23] Close monitoring of kidney function is crucial to minimize nephrotoxic effects.[18] Maintaining adequate hydration can also decrease the likelihood of nephrotoxic events.[24] Studies show that antioxidant administration, most notably deferoxamine,  can alleviate the toxic events produced in the kidneys.[24]

Neurotoxicity

Tobramycin causes neuromuscular blockade by interfering with acetylcholine release.[25] Patients with diseases affecting the neuromuscular junction, such as myasthenia gravis (MG), should not take aminoglycosides.[25] This group of antibiotics can trigger or exacerbate symptoms of MG.[25] If a patient with MG is taking tobramycin and starts to deteriorate, it is best to discontinue tobramycin or to reduce the dosage.[25] Aminoglycosides are also known to cause the drug-induced myasthenic syndrome, which is a reversible disorder in patients who otherwise did not have neuromuscular transmission defects.[26] The symptoms with the drug-induced myasthenic syndrome will occur soon after the drug starts but will cease upon stopping the medication.[26]

Tobramycin is a powerful and effective aminoglycoside, approved for complicated infections with various indications. Because of having a weak binding affinity to the rRNA of prokaryotes, it can cause serious adverse events in patients.[2] It is essential to monitor the patient for side effects and intervene promptly. Educating the patient about these possible effects and close monitoring can help avoid detrimental outcomes. All members of the healthcare team, including clinicians, nursing staff, and pharmacists, should play an active role in coordinating the care to minimize and early detection of adverse events. Taking preventative measures to avoid the toxic side effect profile is crucial. Assessing a patient’s renal function, keeping a patient well-hydrated, and considering antioxidants will help prevent injury kidney. The ordering clinician should consult the pharmacy department for dosing, interactions, and appropriateness of coverage. Nursing will administer the drug, watch for adverse events, and monitor treatment effectiveness, informing the clinicians of any issues that arise.

With antibiotic resistance becoming more and more prominent, it is also essential that the healthcare team only prescribes tobramycin when necessary. This approach will allow tobramycin to continue working well and effectively in the community. With too many prescriptions written, bacteria can become resistant over time. That is why involving a board-certified infectious disease pharmacist who can access the latest antibiogram data should be on the case. As an interprofessional team, it is also important to avoid prescribing tobramycin in patients with neuromuscular junction disorders because of its ability to decrease acetylcholine. With the team approach helping in factoring risks versus benefits for a patient, tobramycin could be a valuable asset in treating difficult systemic infections. [Level 5]