December 01, 2000


 Providing guidance on antimicrobial use

Posted Nov. 15, 2000

Drs. Fajt and Gardner
Dr. Virginia Fajt talks with Dr. Donnie L. Gardner after her presentations.

Supporting development of the Veterinary Antimicrobial Decision Support System and presentations at the AABP conference on susceptibility testing and regimen design are two ways the AABP has been guiding its members on decisions on antimicrobial use.

When completed, the decision support system will be a Web-based database accessible by veterinarians and veterinary students who subscribe. Projected start-up time is 2002 for the initial clinical applications. A subscription fee is being considered, depending on the amount of support from other sources available at release.

The Drug Information Laboratory of the Virginia-Maryland Regional College of Veterinary Medicine will manage the Web site. Tables will list dosage regimens linked to specific animal and disease categories. In an annual progress report released in mid-October, project director, Dr. Mike Apley wrote that two sections will be provided for users examining therapeutic options.

An ancillary therapy section will outline additional interventions determined to increase efficacy. The second section will deal with selection of reasonable antimicrobial regimens. According to Dr. Apley, users will have a choice of proceeding along an empirical therapy track or using pathogen isolation and susceptibility data to aid in regimen determination.

"We are placing a heavy emphasis on first considering on-label application of labeled compounds," Dr. Apley noted. "Next, extralabel use of the labeled compounds will be presented, and only after these two avenues are deemed unproductive by the veterinarian will other extralabel possibilities be explored."

Initially the project team is developing applications for treatment of diseases and associated pathogens in cattle and swine. Later they will work on applications for poultry and small ruminants, if additional funding is acquired.

The VADS System collaborators are working on the initial "template," which deals with bovine neonatal diarrhea. Templates on respiratory tract disease and mastitis are under way, with reproductive tract disease, foot rot, and pinkeye to follow. Data are also being collected and organized to work on the swine applications.

According to Dr. Apley, "Prominently linked to any drug regimen will be information on the potential for this pathogen/drug combination to adversely affect therapy in human medicine, if this information is available."

Cooperation is being established with the Food Animal Residue Avoidance Databank to establish links to the system from the FARAD Web site for slaughter and milk withdrawal recommendations associated with specific extralabel regimens. Dr. Apley noted, "FARAD has been a tremendous resource for the veterinary profession, and we are very grateful that they are willing to provide their expertise in relation to VADS System extralabel regimens."

Collectively, the AVMA, AABP, AASP, Academy of Veterinary Consultants, National Cattlemen's Beef Association, and National Pork Producers Council are contributing $189,000 over three years as start-up money. March 2001 will mark the end of the second year of the funding.

Dr. Virginia Fajt of Iowa State University is a member of the system's project team and represents the AABP on the AVMA Drug Advisory Committee. At the AABP conference she gave back-to-back presentations, the first one on "Preparing for a revolution in antimicrobial susceptibility testing."

She said that the selection of an antimicrobial based on susceptibility testing is no longer as simple as choosing the one labeled "susceptible" by the laboratory, unless you know that the susceptibility determination is based on a clinically validated breakpoint.

Her presentation was geared toward reviewing pharmacokinetic concepts and terminology to enhance veterinarians' ability to make decisions about antimicrobial regimens. Dr. Fajt reviewed methods of susceptibility testing and distinguished between two key terms. The "minimum inhibitory concentration" of an organism is the lowest concentration at which growth is inhibited under specific, standardized conditions, and it defines the relationship between the antimicrobial and the organism. "Breakpoints" are MIC used by laboratories to designate organisms as susceptible (those that grow below the concentration) or resistant (those above), and thereby predict efficacy out in the field. Many laboratories are beginning to provide MIC in addition to breakpoints, making it imperative that veterinarians understand how to use this information.

The Subcommittee for Veterinary Antimicrobial Susceptibility Testing of the National Committee on Clinical Laboratory Standards (phone, 610-688-0100) has established breakpoints for some antimicrobials used in veterinary medicine, including some in cattle. Laboratories use human-derived breakpoints for other drugs commonly used in bovine practice for which veterinary-derived breakpoints have not been established. According to Dr. Fajt, veterinarians need to know whether their susceptibility result is based on a breakpoint that is clinically validated for their application and adjust their conclusions accordingly.

Dr. Fajt said the Veterinary Antimicrobial Decision Support System will "aid practitioners in coming up with a reasonable starting regimen, especially for extralabel drug use."

Her piggyback presentation on "Optimizing antimicrobial regimens" covered concepts of regimen design, building on the information about susceptibility testing. The revolution in testing has been accompanied by a growing understanding of how to design a regimen, she said. To help practitioners design a regimen, the VADS System is being constructed to provide them with information on pharmacology and susceptibility testing in a usable format.