Convenia is a long-acting injectable antibiotic used in cats to treat skin infections, wound infections, and abscesses. Its active ingredient, cefovecin sodium, is a third-generation cephalosporin, meaning it belongs to the same broad family as penicillin-type antibiotics. What makes it unusual is that a single injection provides therapeutic drug levels for about 7 days, and the drug stays in your cat’s body for roughly 65 days before being almost fully eliminated.
How Convenia Works
Like all cephalosporin antibiotics, Convenia kills bacteria by disrupting their ability to build cell walls. Without intact walls, bacterial cells break apart and die. This makes it a bactericidal drug, meaning it actively kills bacteria rather than simply slowing their growth.
Convenia is effective against several common bacterial culprits behind skin and soft tissue infections in cats. In laboratory testing, 100% of Pasteurella multocida isolates (a bacterium frequently involved in bite wound infections) were sensitive to the drug. Beta-hemolytic streptococci were also 100% sensitive, and about 93% of Staphylococcus pseudintermedius strains were susceptible. It does have limits: it has no effect on Pseudomonas aeruginosa, and only about 59% of E. coli strains tested were sensitive. So it’s well suited for skin infections and bite wounds but not a good fit for every type of bacterial problem.
Why Vets Choose a Single Injection
The biggest practical advantage of Convenia is that it eliminates the need to give your cat oral antibiotics at home. Anyone who has tried to pill a cat twice a day for 10 to 14 days understands the appeal. A single shot given under the skin at the vet’s office replaces that entire course of treatment. This is especially useful for feral or semi-feral cats, cats that refuse oral medication, and situations where an owner’s schedule makes consistent dosing difficult.
The tradeoff is that once the injection is given, the drug cannot be taken back. If your cat has a bad reaction to an oral antibiotic, you can simply stop giving it. With Convenia, the drug will remain active in your cat’s system for weeks. It takes approximately 65 days for 97% of the dose to clear the body, based on a half-life of about 13 days. That’s something worth understanding before agreeing to the injection.
Common Side Effects
In FDA clinical trials involving 147 cats treated with Convenia, the most frequently reported side effects were mild and digestive in nature:
- Vomiting: 10 out of 147 cats
- Diarrhea: 7 out of 147 cats
- Decreased appetite: 6 out of 147 cats
- Lethargy: 6 out of 147 cats
Notably, cats on Convenia actually had less diarrhea than cats in the control group receiving a traditional oral antibiotic (7 cases versus 26). One cat in a separate study developed diarrhea that lasted 42 days after treatment before resolving on its own. Some cats in the trial showed mildly elevated kidney and liver values on blood work afterward, though none developed clinical signs of organ problems.
Serious Reactions
Rare but serious adverse events have been reported through post-market surveillance in foreign countries. These include anaphylaxis (a severe allergic reaction), seizures, tremors, facial swelling, hemolytic anemia (destruction of red blood cells), injection site reactions such as hair loss or skin damage, and in some cases, death. These reports come from voluntary submissions rather than controlled studies, so exact rates are unknown, but they underscore why the long duration of the drug matters. If a serious reaction develops, the drug cannot be removed from your cat’s system.
Convenia is contraindicated in any cat with a known allergy to cephalosporins or penicillins. If your cat has ever had a reaction to either class of antibiotic, this drug should not be used.
Cats Who Should Not Receive Convenia
Beyond allergy concerns, several other groups of cats should avoid this drug. Safety has not been established in kittens younger than 4 months, so it is not recommended for very young animals. European labeling specifically cautions against use in cats with kidney dysfunction, which is relevant because chronic kidney disease is extremely common in older cats. Cats with diabetes or chronic urinary tract infections often have some degree of kidney compromise, making Convenia a potentially risky choice for them as well.
Pregnant and lactating cats should not receive Convenia. Cats that have been treated should not be used for breeding for at least 12 weeks after the last injection, which aligns roughly with the drug’s long elimination timeline.
What to Expect After the Injection
Your vet gives Convenia as a single shot under the skin, typically between the shoulder blades. Most cats tolerate the injection without much fuss. Therapeutic drug levels kick in quickly and are maintained for approximately 7 days against the target bacteria. If the infection hasn’t resolved after that window, your vet may recommend a second injection, though this is done on a case-by-case basis.
Because the drug lingers in the body for over two months, you may be asked to watch for delayed side effects even weeks after the injection. Vomiting, prolonged diarrhea, loss of appetite, unusual lethargy, or any swelling around the face or injection site are all worth reporting to your vet promptly. Most cats sail through treatment without any noticeable issues, but the inability to “undo” the injection means paying attention during that long elimination window is worthwhile.