Convenia starts working within hours of injection, and most pet owners notice visible improvement in their dog’s or cat’s infection within two to three days. The drug reaches effective levels in the bloodstream quickly after the single shot is given under the skin, then continues fighting bacteria for up to 14 days.
What to Expect in the First Week
The most dramatic changes happen in the first seven days. In FDA clinical trials for cats with wounds and abscesses, purulent discharge dropped from 95.5% of animals on day zero to just 12.4% by day seven. Swelling went from nearly universal (98.9%) to about a third of cats (34.8%) in that same window. Redness improved too, though it was the slowest sign to resolve, still present in about 45% of cats at the one-week mark.
Dogs followed a similar pattern. Purulent discharge fell from 68.6% to 12.2% in the first week. For dogs with abscesses specifically, 89.3% were considered cured by day seven. Infected wounds took slightly longer, with about 78% cured at the one-week check. Swelling and redness improved but often lingered, with about half of dogs still showing some redness at day seven.
Full Resolution Takes Closer to Two Weeks
While you’ll likely see encouraging signs early on, complete healing typically takes the full 14-day course. By day 14, nearly 98% of cats in clinical trials had all signs of skin infection reduced to mild or absent. In cats, purulent discharge was present in only 1.2% of animals, swelling in about 11%, and redness in about 12%. By day 28, all three signs had dropped to zero.
For dogs, 100% of abscesses were cured by day 14, and 96% of wounds had resolved. Skin infections like folliculitis (infected hair follicles) hit about 92% cure rates at two weeks. Overall, 92.4% of treated dogs had their infection fully resolved or significantly improved by the final assessment.
Why One Shot Lasts So Long
Convenia’s unusually long duration comes down to how tightly the drug binds to proteins in your pet’s blood. In cats, 99% of the drug attaches to blood proteins, which prevents the kidneys from filtering it out quickly. In dogs, about 90% binds. This protein binding creates a slow-release effect: the drug gradually detaches and becomes active over days rather than being eliminated in hours like most antibiotics.
The result is a long elimination half-life, meaning it takes 5.5 days in dogs and nearly 7 days in cats for the body to clear just half of the drug. Therapeutic concentrations are maintained for roughly 7 to 14 days depending on the type of bacteria being targeted. Some bacterial strains are more sensitive to the drug, so lower concentrations still work against them for a longer window.
What Convenia Treats
Convenia is FDA-approved for skin and soft tissue infections in dogs and cats, including abscesses, wounds, and bacterial skin infections like folliculitis and pustules. It’s particularly popular for cats because giving oral antibiotics twice daily to a cat for two weeks is, to put it mildly, a challenge. A single injection at the vet’s office eliminates that struggle entirely.
The drug is not approved for use in puppies or kittens under 8 weeks old, and it should not be given to pets with a known allergy to penicillin or cephalosporin-type antibiotics. It’s also contraindicated in small herbivores like rabbits and guinea pigs.
Side Effects to Watch For
Convenia is generally well tolerated. The most common side effects are mild gastrointestinal issues: vomiting, diarrhea, decreased appetite, or lethargy. These typically appear within the first day or two after injection.
Because the drug stays in the body for weeks, side effects can potentially linger longer than they would with a standard oral antibiotic. This is worth knowing, because if your pet does have an adverse reaction, there’s no way to “stop” the medication once it’s been injected. Allergic reactions are rare but can include skin rashes, fever, difficulty breathing, or collapse. If you notice any of these signs, contact your vet immediately.
When a Second Injection May Be Needed
If you’re not seeing meaningful improvement by day seven, or if the infection worsens at any point, your vet may want to reassess. Some deeper or more stubborn infections require a second injection, typically given 14 days after the first. Dogs with certain skin infections in the FDA trials received up to three injections spaced 14 days apart for more complex cases. Your vet will decide based on how the infection is responding, since a second dose adds another full 14-day course of antibiotic exposure to your pet’s system.