Powdered amoxicillin for cats needs to be mixed with a specific amount of water before you can give it as a liquid dose. The process is called reconstitution, and getting it right ensures your cat receives the correct concentration of medication with every syringe. Most veterinary amoxicillin powder comes in a bottle with instructions, but if the label is unclear or your vet sent you home without a walkthrough, here’s exactly how to do it.
What You Need Before Mixing
You’ll need the amoxicillin powder bottle, clean drinking water (tap water is fine in most areas, though some vets recommend distilled), and a way to measure the water precisely. An oral dosing syringe works well for measuring smaller volumes. The bottle itself is designed to be the mixing container, so you won’t need a separate bowl or cup.
Check the label on your bottle for two things: the concentration (commonly 50 mg/mL for veterinary formulations) and the total bottle size. These determine how much water to add. A common veterinary size is an 80 mL bottle of 50 mg/mL amoxicillin, which requires 59 mL of water. If your bottle came from a human pharmacy (which vets sometimes prescribe from), the water volumes differ by strength and bottle size. For example, a 100 mL bottle of 250 mg/5 mL suspension needs 73 mL of water, while a 150 mL bottle of the same strength needs 110 mL. The exact amount is usually printed on the label or on a sticker your pharmacist added.
Step-by-Step Mixing Process
Start by tapping the bottom of the bottle against your palm or a countertop several times. The powder compacts during shipping and storage, so tapping loosens it and lets it flow freely. This step matters more than it seems. Clumped powder won’t dissolve evenly, and you can end up with inconsistent doses.
Next, measure out the total water volume listed on the label, but only add about one-third of it to the bottle first. Close the cap tightly and shake vigorously for 15 to 20 seconds. This initial smaller amount of water wets the powder thoroughly without creating a thick paste that’s hard to break up. Then add the remaining two-thirds of the water, cap the bottle again, and shake vigorously until the powder is fully dissolved and the liquid looks smooth and uniform. If you see clumps or dry powder stuck to the bottom, keep shaking. You can also let it sit for a minute, then shake again.
The reason for adding water in stages is simple: dumping all the water in at once tends to trap dry powder in clumps that float or stick to the sides. The two-stage method prevents this and gives you an even suspension.
Giving the Dose to Your Cat
Amoxicillin suspension can be given with or without food. Giving it with a meal helps prevent stomach upset, which is the most common side effect. Use an oral syringe to draw up the exact dose your vet prescribed, then gently squirt it into the side of your cat’s mouth, aiming toward the cheek rather than straight down the throat. This reduces gagging and spitting.
Shake the bottle well before every dose. The medication settles between uses, and skipping this step means early doses may be too strong while later ones are too weak. The typical dosing schedule for cats is two to three times per day, depending on the condition being treated. Stick to whatever interval your vet specified, and finish the entire prescribed course even if your cat seems better.
Storage After Mixing
Once reconstituted, amoxicillin suspension should be stored in the refrigerator. It stays effective for 14 days from the date you mix it. After that, the medication breaks down and should be discarded, even if there’s liquid left in the bottle. If refrigeration isn’t possible, it can be kept at room temperature (around 68 to 77°F) for the same 14-day window, though refrigeration is preferred.
Some cats actually prefer the chilled liquid because it’s slightly less bitter. If your cat fights every dose, try warming the syringe slightly in your hands for a few seconds before administering, which can take the edge off the cold without affecting the medication.
Side Effects to Watch For
Most cats tolerate amoxicillin well, but mild digestive issues are common. Decreased appetite, loose stools, or occasional vomiting can happen, especially in the first day or two. These usually resolve on their own.
More serious reactions are rare but worth knowing about. If your cat develops facial swelling, a skin rash, difficulty breathing, or stops eating entirely for more than a day, stop the medication and contact your vet. Prolonged appetite loss in cats is specifically flagged as a concern with amoxicillin, since cats that don’t eat for several days can develop liver problems unrelated to the antibiotic itself.
Disposing of Unused Medication
After the 14-day window, or once your cat finishes the prescribed course, discard any remaining liquid. The FDA recommends mixing leftover medication with something unpleasant like used coffee grounds or cat litter, sealing it in a bag or container, and throwing it in the household trash. Many veterinary offices and pharmacies also accept unused medications through take-back programs if you’d prefer not to trash it. Don’t pour it down the drain unless the label specifically says to.