Why one lick equals medication exposure
When your 5 kg cat groomed the medicated ear, he ingested concentrated droplets meant for external use only—essentially drinking the dose. Cats' saliva spreads liquids across their fur, so what seems like a quick lick may have delivered multiple tongue-fulls of medication. Antibiotics like gentamicin bind to moisture, making wet ear discharge a perfect carrier for overdose.
The second cat's larger size doesn't guarantee safety—medications dosed by weight have narrow safety margins. Watch for excessive lip-licking or swallowing motions in the next hour, signs he's trying to clear the bitter taste and possibly ingesting more residue from his own fur.
How shared grooming complicates treatment
Multi-cat households face medication domino effects—what one cat receives, others may ingest through social grooming. Your second cat likely licked not just the ear but also the first cat's paws and face where medication was transferred. This means exposure could continue for hours as they groom each other or themselves.
Separate the cats temporarily and wipe both with a damp cloth, focusing on the ears, paws, and muzzle. Use plain water—soaps may increase absorption. Check bedding too—if the first cat shook his head, medication may have sprayed onto shared sleeping areas.
When weight differences don't protect
A 1 kg size difference between cats seems significant, but with potent ear medications, both fall into the 'small animal' risk category. The 5 kg cat's larger body may process the drug slightly better, but his liver and kidneys still face the same metabolite overload—just stretched over slightly more time.
Monitor water intake closely for both cats over the next 48 hours. Increased drinking suggests the kidneys are struggling to filter the medication, while decreased drinking could indicate nausea. Neither cat should share water bowls during this period—medication can be excreted in saliva.
The hearing risk you can't see
Some ear medications carry ototoxic risks—they can damage inner ear structures responsible for balance and hearing. While vomiting is obvious, hearing loss develops silently. Test this by rattling keys behind each cat when they're relaxed—failure to turn their ears toward the sound suggests impairment.
Balance checks matter too: place each cat on a non-slip surface and observe their posture. A healthy cat distributes weight evenly on all four paws—leaning or wide stance hints at inner ear disturbance. These signs may appear 3-5 days post-exposure, requiring immediate veterinary assessment even if other symptoms seem mild.
The step-by-step response, from the first minute to the vet visit, is in our Ear Infection Medication Overdose emergency guide.