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VetVine Client Care
Dosing Frequency For IV Gentamicin
Emergency & Critical Care
Contributed by Melissa Holahan, DVM, DACVECC
A VetVine Member asked me this question regarding the dosing of IV gentamicin:
My understanding is that gentamicin is a concentration-dependent antibiotic and, therefore, benefits from lower dosing frequency (q24h) to avoid nephrotoxicity while still being effective.
My practice has been using q8h dosing but I worry about the adverse effects of this dosing frequency. I know that Plumb's has a note about q24h dosing. Any suggestions?
The bactericidal efficacy and the post-antibiotic effect of aminoglycosides correlates with peak concentrations and, thus, single daily dosing of concentration-dependent antibiotics (i.e. aminoglycosides) is best. In contrast, the toxicity of aminoglycosides correlates with trough concentrations, which is why it's safer to dose once daily instead of two to three times daily. You could also be selecting for resistance if dosing every 8 hours as you are likely not reaching effective concentrations (ideally should be four to eight times the MIC of the target organism).
For any aminoglycoside use I recommend the following:
1. Choosing the least nephrotoxic aminoglycoside (i.e. Amikacin is less nephrotoxic than Gentamicin)
2. Ensure that the patient is well hydrated (either on IV fluids or eating / drinking normally)
3. Check daily fresh (ideally evaluated immediately after collection) urine for urine casts. Free-catch is fine for this purpose but serial monitoring is key. I will check a pre-aminoglycoside urine for a baseline then once daily prior to each aminoglycoside dose.
4. Baseline renal panel and repeat if any concerns but since aminoglycosides cause tubular damage first you will see urine casts and a change in urine osmolality before kidney enzyme elevation occurs. Aminoglycoside-induced nephrotoxicity is reversible if caught early and discontinued.
5. Using once daily dosing and using combination therapy (aminoglycosides work synergistically with Beta-lactam antibiotics).
6. Maximum treatment duration that I'm comfortable with is 7-10 days but some will treat longer.
As an aside, I work at a larger referral / speciality hospital and probably reach for an aminoglycoside once or twice a year. I will typically only reach for Amikacin when I have a culture and sensitivity supporting its use in sepsis, septic peritonitis or severe dermatologic infections (MRSA, etc.).
I've also occasionally used it in severe parvoviral enteritis / sepsis puppies for gram negative coverage when Enrofloxacin isn't the most appropriate. The other option I'll reach for in these puppies is Cefoxitin.
The only benefit to Gentamicin used to be the cost but they are now both pretty reasonable.
There isn’t much research in veterinary medicine but you can look at the following as a reference: Small Animal Clinical Pharmacology & Therapeutics. 2nd edition. 2011
Originally posted on April 16, 2014