Merck Manual

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Pet Owner Version

Guidelines for the Use of Antibiotic Drugs


Dawn Merton Boothe

, DVM, PhD, Department of Anatomy, Physiology, and Pharmacology, College of Veterinary Medicine, Auburn University

Reviewed/Revised Jul 2011 | Modified Nov 2022

Antibiotic drugs are commonly used in veterinary medicine to treat infectious diseases that are caused by bacteria and certain other microorganisms. There are many different classes of antibiotics available for use in animals, including penicillins, cephalosporins, cephamycins, aminoglycosides, quinolones, sulfonamides, tetracyclines, and macrolides. Some are effective against a wide range of organisms, while others are more closely targeted (for example, they may be effective against some bacteria but less effective against other bacteria). Thus, antibiotics are often referred to as broad-spectrum or narrow-spectrum drugs, respectively.

Successful antibiotic treatment is based on 4 principles: 1) identifying the disease-causing agent and selecting the appropriate drug for treatment; 2) attaining effective concentrations of the drug at the site of infection for a sufficient period of time; 3) choosing a dose rate, frequency, and method of administering the dose that maximizes the likelihood of a cure, prevents relapse, and minimizes the risk of developing resistance while causing no harm to the animal; and 4) using specific and appropriate supportive treatment to improve the animal’s ability to overcome the infection and associated disease conditions.

The emergence of bacteria that are resistant to currently available antibiotics within the animal or human population is of great concern. When resistance occurs, previously successful drugs can no longer be considered effective treatment, and new drugs must be developed. Resistance may develop in several different ways. However, when used properly (that is, the right antibiotic is used and it is given as prescribed for the appropriate amount of time), antibiotics are less likely to contribute to the selection of antibiotic-resistant organisms.

When given a prescription from your veterinarian for your pet, make sure that it is given exactly as instructed and that the entire prescription is given. Not following dosage schedules or not giving all of the prescription can cause a relapse, a reinfection, or development of antibiotic-resistant organisms.

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