Antibiotic Duration And Spectrum

Lexis writes: My cat Max, 19 months old, had a large open wound Friday. His skin was torn and you could see the muscle on his thigh. We don’t know how this happened since he is an outdoor cat during the day. We took him to the veterinarian on Saturday and they flushed and closed the wound. He also got an injection of Convenia. First when he was examined on Saturday he had a temperature of 103. It’s Monday now and his temperature is over 104. I went back to the veterinarian and got another antibiotic injection, Baytril, and IV fluids. I don’t understand why the first antibiotic Convenia didn’t work since is a long-lasting antibiotic. I’m concerned about his fever and how long it’s going to take this to be resolved.  Thanks!



Puddles is a really sweet kitty, and doesn't mind a Convenia injection.
Puddles is a really sweet kitty, and doesn’t mind a Convenia injection.

The effectiveness of an antibiotic is different from its duration. Antibiotics are used to kill bacteria. Effectiveness is primarily based on the bacteria’s susceptibility to a particular antibiotic. The only way to know for sure what antibiotic will work is to perform bacterial culture and sensitivity.

However, in most cases we prescribe (or, in the case of Convenia, administer) antibiotics based on experience. We look at a wound, ear, or other infected body part and choose an antibiotic according to the way the patient presents.

Alternatively, we may obtain specimens for bacterial culture and sensitivity (C/S), but begin an antibiotic while we await the results of the test. Typically C/S takes between three and ten days to yield an answer.

In the vast majority of cases symptomatic therapy works. If, on the other hand, the first-chosen medication doesn’t cover the spectrum of bacteria causing the infection, another antibiotic must be chosen.

There are two major differences between Convenia and Baytril. One is duration. Convenia lasts about 14 days, Baytril must be redosed every 24 hours. The other is spectrum. The two antibiotics simply kill different bacteria.

The good news for Max is that Baytril and Convenia work well together, greatly increasing the likelihood that he will improve on the combination, and even better than either antibiotic alone.




A fever of 104 in a person would be cause for concern. Cats with compartmented infection, such as an abscess, can often spike fevers of 107 and sometimes higher. A fever has a purpose. It speeds up metabolism, blood flow and the immune system. It cannot be allowed to go on too long, but as the infection is controlled, the fever will go down, too.


Next, I’d like to address your statement, “We don’t know how this happened since he is an outdoor cat during the day.” Actually, you’ve answered your own question. Max probably went outside, ran into a neighborhood stray, who proceeded to pick a fight. Even though Max was on his own territory, the other cat was trying to protect “his” territory and inflicted a wound, which quickly became infected.

Indoor cats don’t have this problem. They don’t get hit by cars, eaten by dogs or become exposed to untreatable diseases such as Feline Immunodeficiency Virus.

Please consider making Max a totally indoor cat.

See you tomorrow, Dr. Randolph.



covenia, convina, convinia, covinia

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