Dear Dr. John,
Our old dog has all kinds of issues with his heart, eyesight, ears, and skin. He takes cardiac medications daily and our vet gives us medication for his ears and skin when he has infections that flare up. My question: Do antibiotics lose their efficacy over time? It seems that the skin problems repeatedly pop up and the drug, Cephalexin, is what he is given. Over time, the dosage and time needed to fight off skin infections has seemingly increased. Is that typical? We now also must use shampoos to help stop the skin infections. Eventually, the infection always clears but invariably it returns after some time. Could he also have a weak immune system? K.M.
Dear K.M.,
The timing of your questions is uncanny because, as I write this, I am preparing to go to the United Nations in New York to speak as part of day of hearings on the topic of antimicrobial resistance (AMR). Antibiotics can lose their efficacy over time. I attended a brilliant lecture years ago on the continuing evolution of antibiotic development to fight off bacterial infections.
Historically, different antibiotics might have been very popular and then fell out of favor due to decreasing efficacy. This is simply because different bacteria developed resistance to different antibiotics. When used less, they had the potential to renew their ability to fight bacteria.
Cephalexin is a commonly used antibiotic for skin infections with good results, as are other cephalosporins which is a class of antibiotics. I cannot say whether the increased dosage and duration of antibiotic treatment are due to resistance of whatever bacteria are causing the infections but since it still works, there may be no need to change or worry. Veterinarians and all medical personnel can always obtain a culture and then test sensitivity of the culture to various antibiotics.
I would trust your veterinarian since it appears your dog usually responds favorably. If your veterinarian had any unanswered questions, they might have tested your dog’s immune system. Veterinarians are well trained and judicious in the use of antibiotics.
Dr. John de Jong is President of the World Veterinary Association. He owns and operates the Boston Mobile Veterinary Clinic and can be reached at 781-899-9994.