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U.S. Department of Health and Human Services

Animal & Veterinary

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FDA Investigates Illegal Extralabel Use of Sulfonamides (Sulfa Drugs) in Dairy Cows

FDA Veterinarian Newsletter July/August 2005 Volume XX, No IV

Some veterinarians have been illegally using sulfonamides (sulfa drugs) in lactating dairy cows, according to information reported to the Center for Veterinary Medicine (CVM).

For example, during a routine inspection of a Wisconsin dairy operation in August, a State inspector found containers of unapproved sulfa drugs in the milk barn—evidence of improper sulfa drug use. The regional milk specialist noticed a box of six tubes marked SXT, indicating a sulfa drug inside. The drug had been prescribed by a veterinarian, who later received a warning against prescribing any sulfa drug that was not specifically approved for use in lactating dairy cattle.

CVM’s concern is that the use of a small amount of a sulfonamide drug in a lactating dairy cow can result in the contamination of milk from several hundred cows when mixed in a bulk tank. The contamination levels could be high enough to present a risk to public health.

CVM issued a “CVM UPDATE” in August warning veterinarians that FDA’s rules prohibit the extralabel use of sulfa drugs in lactating cows. It also said, “CVM has received some information indicating that sulfonamides, some in combination with trimethoprim, are being prescribed for use in treating conditions in lactating dairy cattle for which they are not approved.” The article stated that unapproved use of sulfonamides is a frequent cause of violative residues in food-producing animals.

In some cases, FDA can permit extralabel, or off-label, use of FDA-approved animal and human drugs. The extralabel provisions are part of the 1994 Animal Medicinal Drug Use Clarification Act and its implementing regulation, Title 21, Code of Federal Regulations, Part 530 (21 CFR 530). However, FDA’s extralabel drug use rule specifically prohibits the use of some drugs in an extralabel fashion, including sulfa drugs in lactating dairy cows. (See box for other drugs prohibited from extralabel use.)

According to Dr. Mike Talley, CVM’s milk safety specialist, the only currently marketed drug approved for use in lactating dairy cows 20 months of age or older is sulfadimethoxine as an injectable or oral bolus. Use of the product also carries with it the responsibility to discard the cow’s milk for a certain period of time after treatment as prescribed on the -labeling.

CVM has also found that veterinarians are misusing the approved injectable product by intramammary infusion to treat mastitis. CVM is also concerned about veterinarians increasing the dose or treating conditions in lactating cattle not on the approved labeling. Administering a drug in an unapproved manner is another form of extralabel drug use and is prohibited in the case of sulfa drugs in lactating dairy cows.

The drug is also approved as a sustained release oral bolus, in beef cattle. However, CVM has received reports that veterinarians use the sustained release boluses to treat lactating dairy cattle.

[Boxed text follows]

Drugs prohibited from extralabel use in all food-producing animals:

  • Chloramphenicol
  • Clenbuterol
  • Diethylstilbestrol
  • Dimetridazole
  • Furazolidone, nitrofurazone, other nitrofurans
  • Fluoroquinolones
  • Glycopeptides
  • Ipronidazole
  • Other nitroimidazoles
  • Phenylbutazone in female dairy cattle 20 months of age or older
  • Sulfonamide drugs in lactating dairy cattle (except approved label use of sulfadimethoxine, sulfabromomethazine, and sulfaethoxypyridazine)