Gentamicin

Gentamicin is an aminoglycoside antibacterial used for serious infections caused by susceptible organisms, particularly aerobic gram-negative bacilli. Parenteral treatment is used in selected companion-animal and equine patients, sometimes in combination with a beta-lactam. Local formulations have ophthalmic, otic or other site-specific uses, while oral livestock products target intestinal rather than systemic infections.

Group

Aminoglycoside antibacterial

Mechanism of Action

Gentamicin enters susceptible bacteria and binds the 30S ribosomal subunit, causing misreading of messenger RNA and disruption of protein synthesis. Interaction with the gram-negative outer membrane also impairs membrane integrity and facilitates uptake. These combined effects produce rapid, concentration-dependent bacterial killing with a post-antibiotic effect. Cellular uptake depends on conditions supporting energy-dependent transport, contributing to its activity against aerobic organisms.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infection	9–14 mg/kg	SC, IM, IV	Every 24 h	Do not use in: Renal insufficiency
Sighthound bacterial infection	6 mg/kg	IV	Every 24 h	Greyhound regimen; applicability to other sighthounds is less established.
Sighthound bacterial infection	9 mg/kg	SC, IM	Every 24 h	Greyhound regimen; applicability to other sighthounds is less established.

Cat

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infection	5–8 mg/kg	SC, IM, IV	Every 24 h	Do not use in: Renal insufficiency

Horse

Use / stage	Dose	Route	Schedule	Instructions
Adult bacterial infection	4–6.6 mg/kg	IM, IV	Every 24 h	Do not use in: Renal insufficiency
Neonatal foal infection	12–14 mg/kg	IM, IV	Every 24 h	Do not use in: Renal insufficiency; Foals younger than 2 weeks.

Pig

Use / stage	Dose	Route	Schedule	Instructions
Young-pig bacterial infection	15 mg/kg	SC, IM	Every 24 h	Do not use in: Renal insufficiency
Older-pig bacterial infection	10 mg/kg	SC, IM	Every 24 h	Do not use in: Renal insufficiency
Enteric infection	Reference only	PO		Do not use in: Renal insufficiency; 1.1–2.2 mg/kg in drinking water for 3 days; source does not clearly define dose frequency or water-intake assumptions.
Medicated-water colibacillosis treatment	Reference only	PO		1.1 mg/kg/day in drinking water for three days; the source gives 25 mg per gallon. Consumption-dependent dosing must be reconciled with body weight and actual water intake.
Medicated-water dysentery treatment	Reference only	PO		2.2 mg/kg/day in drinking water for three days; the source gives 50 mg per gallon. Water-intake-based medication cannot be flattened into a bolus dose.

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Neonatal calf infection	12–15 mg/kg	IV, IM	Every 24 h	Do not use in: Renal insufficiency; Calves younger than 2 weeks; prolonged residue concerns.
Adult bacterial infection	5–6 mg/kg	IM, IV	Every 24 h	Do not use in: Renal insufficiency

Chinchilla

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2–4 mg/kg	SC, IM	Every 8–24 h	Maintain hydration; monitor for nephrotoxicity and ototoxicity.

Gerbil

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2–4 mg/kg	SC, IM	Every 8–24 h	Maintain hydration; monitor for nephrotoxicity and ototoxicity.

Guinea Pig

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2–4 mg/kg	SC, IM	Every 8–24 h	Maintain hydration; monitor for nephrotoxicity and ototoxicity.

Hamster

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2–4 mg/kg	SC, IM	Every 8–24 h	Maintain hydration; monitor for nephrotoxicity and ototoxicity.

Mouse

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2–4 mg/kg	SC, IM	Every 8–24 h	Maintain hydration; monitor for nephrotoxicity and ototoxicity.

Rat

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2–4 mg/kg	SC, IM	Every 8–24 h	Maintain hydration; monitor for nephrotoxicity and ototoxicity.

Ferret

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	5 mg/kg	SC, IM	Every 24 h	Use only when susceptibility and clinical need justify the nephrotoxicity risk.

Rabbit

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	5–8 mg/kg	SC, IM, IV	Every 24 h	For IV use, the described regimen dilutes into 4 mL/kg saline and infuses over 20 minutes. Monitor renal function.

Ratite

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	5 mg/kg	IM	Every 24 h	Last-resort option because visceral gout can occur.

Indications

Parenteral treatment of serious susceptible aerobic bacterial infections in dogs, cats and horses, including selected gram-negative sepsis, respiratory, urinary or soft-tissue infections.
Combination treatment of selected severe bacterial infections, including neonatal foal sepsis, when an aminoglycoside component is appropriate.
Local treatment of susceptible bacterial ocular, otic or other focal infections with a corresponding veterinary formulation.
Oral treatment or control of susceptible Escherichia coli-associated colibacillosis in pigs with an indicated product.
Treatment or control of susceptible swine dysentery with an oral gentamicin product carrying that indication.

Contraindications

Renal dysfunction
Correct dehydration and electrolyte depletion before treatment.

Interactions

Loop diuretics increase renal and ototoxic risk.
Anesthetic agents may enhance neuromuscular blockade.
Do not mix with other antibiotics in a vial, syringe or line.

Adverse effects

Nephrotoxicity
Ototoxicity and vestibular injury
Neuromuscular blockade

Toxicity

Persistent trough exposure increases renal damage; auditory or vestibular injury may be irreversible.

Preparations

Preparation	Form	Strength	Route
Gentamicin injection 50 mg/mL	Injection	50 mg / mL	IV, IM, SC
Gentamicin injection 100 mg/mL	Injection	100 mg / mL	IV, IM, SC
Gentamicin oral solution 50 mg/mL Porcine enteric use; oral administration does not treat systemic infection.	Oral Liquid	50 mg / mL	PO

Monitoring and Administration

Monitor renal parameters, urinalysis and drug concentrations where available. Once-daily trough should be very low; impaired clearance requires reassessment.

Food-animal systemic use can leave very prolonged renal residues; do not apply short oral-product withdrawal times to injections.