Gentamicin Calculator for Dogs (Otic, Ophthalmic, Systemic)

PuppaDogs publishes evidence-based veterinary calculators reviewed against Plumb’s Veterinary Drug Handbook, ACVIM consensus statements, AAHA guidelines, and the manufacturer label. Read our editorial policy and how we verify drug doses.

Gentamicin for Dogs – Multi-Formulation Aminoglycoside

Gentamicin covers gram-negative + some gram-positive bacteria. Multiple formulations.

Otic (Most Common Veterinary Use)

Products

• Mometamax (gentamicin + mometasone + clotrimazole)
• Otomax (gentamicin + betamethasone + clotrimazole)
• Gentocin Otic

Protocol

• 2-3 drops in affected ear BID
• Clean ear first with vet cleaner
• Massage base of ear
• Duration 7-14 days
• EARDRUM MUST BE INTACT

Ophthalmic

• 0.3% solution or ointment
• 1-2 drops or pea-sized ointment
• 3-4 times daily
• Duration 5-7 days
• Bacterial conjunctivitis
• Corneal ulcer adjunct

Parenteral (IV/IM) – Hospital Use

6-10 mg/kg IV/IM once daily (extended interval dosing)

Reserved for:

• Resistant gram-negative infections
• Pseudomonas
• Severe gram-negative sepsis

⚠ Nephrotoxicity (Systemic)

Monitor:

• Baseline + serial BUN/Cr/USG
• Urine sediment for casts (early sign)
• Discontinue if azotemia
• Adjust dose for CKD
• Avoid concurrent NSAIDs + furosemide
• Maintain hydration
• Drug troughs

⚠ Ototoxicity

• Cochlear (hearing) + vestibular (balance) damage
• Often IRREVERSIBLE
• Risks: ruptured eardrum + otic, prolonged systemic, concurrent furosemide, dehydration
• Senior dogs higher risk
• NEVER use otic with perforated eardrum

Contraindications

• Perforated eardrum (otic)
• Significant renal disease (systemic)
• Myasthenia gravis (neuromuscular blockade)
• Concurrent nephrotoxic drugs (NSAIDs, cisplatin, amphotericin B)
• Severe dehydration
• Pregnancy caution

Alternatives if Eardrum Ruptured

• TrizUltra + Keto (gentamicin-free)
• Systemic antibiotics
• Fluoroquinolone otic

Frequently Asked Questions

How do I use gentamicin ear drops for my dog?

STEP-BY-STEP: 1) VERIFY EARDRUM INTACT – vet otoscopic exam REQUIRED; gentamicin ototoxic if perforated; 2) CLEAN EAR FIRST with vet-approved cleaner (Epi-Otic Advanced, OticClens, Douxo Micellar); fill canal with cleaner; massage base of ear 30 seconds; let dog shake; wipe with cotton (don’t push in); 3) APPLY DROPS – 2-3 drops in affected ear (or product label dose); 4) MASSAGE base of ear 30 seconds to distribute; 5) Allow dog to shake; 6) Wipe excess; 7) BID typically for 7-14 days; 8) Recheck at 7-14 days. EARDRUM INTACT essential – aminoglycoside ototoxic if perforated (permanent hearing/vestibular damage). RESISTANT or PSEUDOMONAS infections need culture + alternative (TrizEDTA + Baytril Otic). RECURRENT otitis = investigate root cause (allergy 75%).

Is gentamicin safe for my dog?

DEPENDS on route. TOPICAL/OTIC/OPHTHALMIC – generally safe with eardrum intact and proper use. SYSTEMIC (IV/IM) – serious nephrotoxic + ototoxic risks; reserved for resistant gram-negative infections with monitoring. NEPHROTOXICITY (systemic): 1) Acute tubular necrosis at high doses or prolonged use; 2) Risk factors: dehydration, concurrent NSAIDs/furosemide, pre-existing CKD; 3) Monitor BUN/Cr/USG + urine sediment (casts early sign); 4) Reversible if caught early; 5) Hydration support critical. OTOTOXICITY: 1) BOTH cochlear (hearing loss) + vestibular (balance) damage; 2) Often IRREVERSIBLE; 3) Otic use with PERFORATED eardrum can cause; 4) Prolonged systemic use; 5) Concurrent furosemide increases risk; 6) Senior dogs higher risk; 7) Verify eardrum intact before otic use. MYASTHENIA GRAVIS: aminoglycosides cause neuromuscular blockade – AVOID. SAFE USE: 1) Topical for non-perforated infections; 2) Short systemic courses with monitoring; 3) Adequate hydration; 4) Avoid drug interactions; 5) Reserve for confirmed susceptibility.

What can I use instead of Mometamax/Otomax if my dog’s eardrum is ruptured?

ALTERNATIVES that AVOID aminoglycosides (gentamicin ototoxic if eardrum ruptured): 1) TRIZULTRA + KETO – tris-EDTA based, no aminoglycoside; effective Pseudomonas + biofilm; 2) SUROLAN (polymyxin B + miconazole + prednisolone) – polymyxin less ototoxic; 3) MOMETAMAX-free combinations; 4) Systemic antibiotics based on culture; 5) BNT (Tresaderm) – thiabendazole/neomycin/dexamethasone – caution with neomycin (also aminoglycoside but lower concentration); 6) Compounded silver nitrate solutions; 7) Topical fluoroquinolones (Baytril Otic) – less ototoxic; 8) Address otitis media if present (X-ray, CT, possibly TECA surgery). VERIFY EARDRUM STATUS with vet otoscopic exam before any topical otic. Some products specifically labeled for use with perforated tympanic membranes. PSEUDOMONAS often resistant – culture essential; combination treatment usually needed. RECURRENT infections need ROOT CAUSE workup: 1) Allergy (atopic, food); 2) Endocrine (hypothyroid, Cushings); 3) Anatomic (stenotic canal – Cocker, Shar-Pei); 4) Foreign body; 5) Neoplasia. Consult veterinary dermatologist or otologist for complex cases.

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References & Further Reading

The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.

1. Plumb DC. Gentamicin.
2. Mometamax, Otomax product information.
3. Hnilica KA. Small Animal Dermatology.
4. WSAVA Otitis Guidelines.
5. ISFM ear treatment guidelines.
6. PuppaDogs. Mometamax Calculator, Otitis Externa Calculator. puppadogs.com.