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Dr. Muse states, "The skin receives only 4% of the heart’s output so effective blood delivery of antibiotic concentrations have a much more difficult time saturating the skin cells in microbe-killing amounts than in organs well perfused with blood such as the liver. At our dermatology clinic we have discovered that about 10% of the ‘allergy’ patients are actually suffering from chronic pyoderma and have not responded well to antibiotics previously used. Sometimes that failure for an infection to clear is due to too low of a dose being given or the dose not being given as often as directed or for as long as directed. In some cases, especially if a culture and sensitivity have not been done, the antibiotic chosen may not be the best choice for the specific bacteria causing the pyoderma."
"There are four principles to keep in mind regarding appropriate antibiotic use," continues Dr. Muse. “One is that the correct choice of antibiotic needs to be made for a particular infection. The second is the proper dose must be given. Third is that the dose must be given at defined intervals because some medications should be given once a day and others four times a day to achieve consistent and effective tissue levels of the antibiotic. And finally, the antibiotic needs to be given long enough to truly effect a cure."
In general, most veterinarians select what they consider to be an appropriate medication, and if the results are not favorable, laboratory identification of the bacteria and testing for the bacteria’s vulnerability to specific antibiotics is done. This is termed "doing a culture and sensitivity."
Should this, however, be done in every situation where an infection is discovered?
According to Mark G. Papich, DVM, Professor of Clinical Pharmacology in the College of Veterinary Medicine at North Carolina State University, "For routine infections, empirical treatment with ‘first line’ drugs can be used without obtaining lab tests (culture and susceptibility tests) first. For refractory infections, or cases that are more serious and/or life-threatening, lab tests are recommended."
Some failures of antibiotic administration might be due to early withdrawal of the drug by the owner when it appears that an infection has "cleared up."
Every veterinarian has experienced the exasperation of faulty owner compliance with prescription instructions. A typical scenario goes like this … the veterinarian sees a patient again for the same problem a few months after prescribing an antibiotic. A different prescription is suggested to fight the infection and the owner says "I’ve still got quite a few left from the last time, Doctor. Should I just start those again?"
So that’s why the medication didn’t work; it wasn’t used for the entire treatment time!
"Another concern regarding indiscriminate use of antibiotics in small animals" states Papich, "is the resistance problem. When animals are exposed to antibiotics, there is a good chance that the endogenous population of bacteria will mutate or acquire resistance factors that may change them from being susceptible to being resistant. When these bacteria later on are the cause of a urinary tract infection, wound infection, or other opportunistic infection, there is a good chance that they will be resistant to standard drugs."
Some antibiotics, such as the tetracyclines, should not be given with dairy products that contain lots of calcium because the calcium binds with the antibiotic and reduces the effectiveness. Some antibiotics, as mentioned, must be given every six hours, some every eight, some every 24 hours. One prescription may need to be given with food and another on an empty stomach. One group of antibiotic might cause severe diarrhea, another could permanently discolor emerging tooth enamel if given to young pups, another group could cause bone marrow suppression, and another could potentially do harm to the auditory nerve and cause permanent deafness.
The moral of this story is to expect antibiotics to be used only when truly needed and then to be used according to the directions. And if your veterinarian seems reluctant to dispense an antibiotic when little Snuffy has the sniffles, now you know why. Take heart that if the sniffles turn in to something worse, antibiotics are available if needed.
Image: Petra Fritz / via Flickr