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U.S. Department of Health and Human Services

Animal & Veterinary

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BST Update

This CVM Update was edited on April 23, 2009 to reflect the sale of POSILAC from Monsanto to Elanco Animal Health, Inc in 2008. The contact number for CVM has been updated.


March 21, 1996

FDA approved Monsanto Company's recombinant bovine somatotropin (rbST) product, Posilac®, in November 1993 after a comprehensive review of the product's safety and efficacy, including human food safety. Posilac® is the only rbST product approved for increasing milk production in dairy cattle. The product has been commercially available since February 4, 1994.

In a March 14, 1995 FDA TALK PAPER, the Agency stated that during the first year of commercial use of Posilac®, a total of 806 reports of adverse effects were reported to Monsanto and submitted to FDA. A CVM UPDATE issued on October 12, 1995, included information on 509 reports of adverse effects reported from February 1 to August 25, 1995.

The following is an update on the adverse experiences to Posilac® reported to FDA from August 26, 1995 through February 3, 1996. During this period, FDA received 144 adverse experience reports (See table below.) It is important to note that a report of an adverse effect in relation to a drug does not itself establish that the effect was caused by the drug. FDA believes that 83 of the 144 reports were possibly associated with the use of Posilac®, and that the other 61 reports were not related to treatment with Posilac®. Also, all of the reported clinical manifestations are known to occur in dairy cattle not supplemented with Posilac®.

Of the 83 reports possibly related to the use of Posilac®, 18 included reproductive disorders, 10 involved digestive disorders, 23 included mastitis, 19 included injection site reactions, 12 included swelling of the udder or abnormal milk, 9 included foot or leg problems, and 17 involved increased somatic cell counts. In some cases, a single report contained multiple conditions.

The number and severity of the reported conditions raise no new animal health concerns about the safety of Posilac®. There is no indication that the drug is any less effective than labeled. In addition, FDA and State regulatory officials have found no indication of a change in the incidence of violative drug residues in milk associated with the commercial use of Posilac®.

Based on the these reports of adverse reactions to Posilac®, FDA finds no cause for concern. However, it is important for dairy farmers to continue to report all adverse reactions associated with the use of rbST. They may report such reactions to Elanco Animal Health, Inc. (the current owner of Posilac®), to FDA through their veterinarian, or directly to FDA's Center for Veterinary Medicine at 1-888-FDA-VETS.


August 26, 1995 through February 3, 1996

The following table summarizes the important clinical manifestations (CM) from the 83 adverse experience reports possibly related to the use of Posilac® from August 26, 1995 through February 3, 1996.

This summary is intended only as a general reference to the type of reactions that veterinarians and dairy farmers have voluntarily reported to the manufacturer or FDA. Therefore, the summary is not by itself a basis for determining drug association for a particular sign, safety or efficacy of the drug, or determining the frequency or incidence rate of a clinical manifestation. Each of the reports may contain one or more CMs, and as a result the number of CMs exceeds the number of reports. All of the reported clinical manifestations are known to occur in dairy cattle not supplemented with Posilac®.

Clinical Manifestation (CM)Number of Reports with the CMEstimated Number of Cows Reported with the CM
Mastitis (clinical)23416
Increased Somatic Cell Counts in Milk17446
Other Udder Abnormalities*12289
Reproductive Disorders**18381
Cardiovascular Disorders11
Digestive Disorders***10171
Foot or Leg Problems9110
Injection Site Reactions19349
Cattle Deaths****24
*Includes udder swelling, udder edema, or abnormal milk.
**Includes decreased fertility, abortions, premature births, and retained placentas.
***Includes anorexia, weight loss, and other digestive tract signs.
****The most commonly reported CM for all dairy cattle drug products is death. This includes cows that were euthanized or slaughtered due to an illness, such as chronic mastitis.

Contact FDA

240-276-9115 FAX
Issued by: FDA, Center for Veterinary Medicine

Communications Staff, HFV-12

7519 Standish Place

Rockville, MD 20855