PetMD Editorial
By PetMD Editorial on Jul. 18, 2014

Drug Info

  • Common Name: Otomax, Mometamax, GenOne
  • Generics: Gentamicin with Corticosteriod
  • Drug Type: Antibiotic with Corticosteriod
  • Used For: Antibiotic used for a wide variety of ear & topical infections
  • Species: Dogs, Cats
  • Administered: Otic / Topical
  • How Dispensed: Prescription Only
  • Available Forms: Various
  • FDA Approved: Yes


Gentamicin (antibiotic) and Betamethasone (corticosteroid) are typically paired together to be used either topically for lesions and cuts or as an otic to treat ear infections caused by bacteria sensitive to Gentamicin.

Gentamicin and Betamethasone with Clotrimazole (antifungal) is used in the treatment of canine acute and chronic otitis externa caused by susceptible strains of yeast and bacteria.

Gentamicin and Mometasone (corticosteroid) with Clomitrazole is used in the treatment of otitis externa in dogs caused by susceptible strains of yeast and bacteria.

Dosage and Administration

Always follow the dosage instructions from your veterinarian.

For topical treatments, remove any excessive hair and clean the lesion and adjacent area before treatment. For treatment of the ear(s), thoroughly clean and dry the ears before treatment.

Apply the prescribed amount of medication to the area that is being treated and, for ear(s), massage the ear(s) so the medication is distributed throughout the ear.


Missed Dose?

If a dose is missed, apply as soon as you remember.  If the dose is close to the next dose, skip the application you missed and resume your regular schedule.

Possible Side Effects

Possible side effects of the ear medication can include loss of hearing, loss of balance and diarrhea, while side effects of the topical medication can include enzyme elevations, weight loss and anorexia. If either medication is ingested, side effects can include increased thirst and increased urination.

Less common side effects could include, increased appetite and weight gain, painting, diarrhea, vomiting and behavior changes.

Contact your veterinarian if you think your pet has any medical problems or side effects during treatment.


If your pet has any allergic reactions to the medication contact your veterinarian immediately. Do not use Gentamicin on animals that are allergic to any of the ingredients and avoid contact with eyes and ingestion of the medication. If ingested in high doses or for extended periods, corticosteroids can cause premature birth, especially towards the end of pregnancy. Please note: Corticosteroids can cause birth defects in dogs, rabbits and rodents.

Animals that use their hearing to perform their work, like seeing eye dogs, should not use this medication as it may impair their hearing and may cause permanent hearing loss.

If corticosteroids are given at high doses or for extended periods of time, it can cause delayed wound healing and compromise the immune system resulting in an increased risk of bacterial or fungal infections.


Store at a temperature between 36-77oF.  Keep out of children’s reach.

Drug Interactions

Consult your veterinarian when giving other medications or supplements while on treatment of a Gentamicin/Corticosteriod as interactions may occur. If ingested, your pet may be at a higher risk of stomach ulcers when corticosteroids are used with non-steroidal anti-inflammatory drugs (NSAIDs) such as Carprofen, Etodolac, Deracoxib or aspirin.

Do not administer other corticosteroids during treatment with this medication and do not use in conjunction with other aminoglycosides, such as Neomycin.

Signs of Toxicity/Overdose

  • Loss of Hearing
  • Loss of Balance
  • Vomiting

If you suspect or know your pet has had an overdose, it could be fatal so please contact your veterinarian, an emergency vet clinic, or the Pet Poison Helpline at (855) 213-6680 immediately.

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