Animal & Veterinary
Think Twice Before Using Gentamicin
by Linda Cline
FDA Veterinarian Newsletter May/June 2003 Volume XVIII, No 3
No one was thinking about drug resi-dues when they treated several hundred head of sick young calves that had just traveled hundreds of miles from dairy farms in Idaho and Washington. They were just trying to keep them alive and save their sight, because many were scouring and suffering with severe pinkeye. Using gentamicin under a veterinarian’s direction seemed to be the most effective treatment when given orally to treat the scours and used as a flush in the calves’ eyes. The calves recovered and in another two months were in good enough shape to be shipped out to feedlots.
Another year would pass before the calves had grown and reached market weight. No one was thinking about drug residues when the calves, now grown to steers, were shipped for slaughter, because no one had treated them at the feedlot. Sampling by USDA at the slaughter plant changed everyone’s thinking when a gentamicin residue was found in the kidney of the steer sampled.
There is no “tolerance” for gentamicin in cattle, because a gentamicin-containing drug has not been approved for use in cattle. Gentamicin is known to bind to the kidney tissue of cattle irregardless of the route of administration and could be a residue concern for 18 months or more. In fact, no withdrawal period has been scientifically established in cattle for those veterinarians searching the literature for direction in an “extra-label” use scenario. No one thought about a drug being sustained in an animal for a year or more, but gentamicin is different and professionals treating cattle need to know this. In this investigation, veterinarians involved in treating the calves recommended a six-month withdrawal period and their colleagues were their source of the withdrawal period. There was a learning experience from this investigation for the professionals involved when they were informed of the unusual residue problems with gentamicin, and subsequently stopped using it in dairy and feedlot cattle.
CVM’s Dr. Mike Talley notes that “veterinarians and producers should be aware that there are approved drugs to treat the conditions described in calves that have much less potential for prolonged residues available for extra-label use if the approved drugs were found not to be effective by the prescribing veterinarian. In addition, the American Association of Bovine Practitioners (AABP), the American Veterinary Medical Association (AVMA), and the Academy of Veterinary Consultants have position papers or resolutions saying that aminoglycosides should not be used for extra-label purposes in cattle.”
Linda Cline is a FDA Investigator in the Sioux City, Iowa Resident Post.