A nurse is caring for a patient who is receiving gentamicin IV for treatment of endocarditis caused by gram-negative bacteria.
Which laboratory value should be monitored closely during gentamicin therapy?

Gentamicin is an example of a concentration-dependent antimicrobial, which means that it achieves increasing bacterial kill with increasing levels of drug.The peak concentration and the area under the concentration curve (AUC) determine the efficacy of these antibiotics.Other examples of concentration-dependent antimicrobials include fluoroquinolones, daptomycin, aminoglycosides, and amphotericin

Choice A is wrong because ciprofloxacin is a fluoroquinolone, which is also a concentration-dependent antimicrobial.

Choice B is wrong because imipenem is a carbapenem, which is a type of beta-lactam antibiotic.Beta-lactams are time-dependent antimicrobials, which means that their bactericidal activity depends on the duration of the effective concentration.

Choice C is wrong because penicillin V is another type of beta-lactam antibiotic, which is also a time-dependent antimicrobial.

Choice D is wrong because metronidazole is a bactericidal agent that has both time- and concentration-dependent properties.However, it is not classified as a concentration-dependent antimicrobial according to the AMEG categorization of antibiotics in the European Union.

Here is why:

• Choice A:Monitor the client’s serum creatinine level.

This is correct because vancomycin can cause nephrotoxicity (damage to the kidneys) and serum creatinine is a marker of kidney function.A high serum creatinine level indicates impaired kidney function and may require dose adjustment or discontinuation of vancomycin.

• Choice B:Monitor the client’s serum vancomycin level.

This is correct because vancomycin has a narrow therapeutic range, meaning that there is a small difference between the effective dose and the toxic dose.Monitoring the serum vancomycin level can help to ensure that the drug is within the therapeutic range and avoid toxicity or suboptimal efficacy.

• Choice C:Infuse the drug over at least 60 minutes.

This is correct because vancomycin can cause a hypersensitivity reaction called “red man syndrome” or “red neck syndrome”, which is characterized by flushing, itching, rash, hypotension and tachycardia.

This reaction is not an allergy but a result of histamine release due to rapid infusion of vancomycin.Infusing the drug over at least 60 minutes can reduce the risk of this reaction.

• Choice D:Observe the client for signs of ototoxicity.

This is incorrect because vancomycin is not known to cause ototoxicity (damage to the ears) in humans.Ototoxicity has been reported in animal studies and in vitro studies, but not in clinical trials or case reports involving humans.

Therefore, there is no need to monitor for signs of ototoxicity such as hearing loss, tinnitus or vertigo.