Antibiotics destroy germs. However an antibiotic can’t tell the difference between good and bad microbes. While it may kill the bacteria causing, say a pneumonia, it may also kill beneficial bacteria in the digestive tract, causing loose stools or diarrhea. Antibiotics are only effective against bacteria and fungi. They are not effective against viruses. Generally speaking there are no true "antiviral drugs" used on dogs or cats.
Generally speaking at the London Veterinary Clinic we often choose a "broad spectrum" antibiotic, one known to kill a wide variety of either bacteria or fungi. At the same time a "culture and sensitivity" test may be conducted. The germ is grown on a culture plate containing tiny discs each containing a different type of antibiotic. Results, available within two days for bacteria, longer for fungi, indicate which antibiotics are likely to be most effective against the disease-causing germ.
Why Antibiotics May Fail To Work
Antibiotics may fail for a number of reasons including:
- The disease-causing germ is resistant to the chosen antibiotic.
- The antibiotic is not effective against the specific disease-causing germ.
- The antibiotic is given at too low a dose or not long enough to eliminate the germ.
- The route of antibiotic administration (by mouth, by injection) does not allow adequate quantities of the antibiotic to get to the site of infection.
- The antibiotic cannot get to the infection because it is in an abscess or surrounded by dead tissue.