June 19, 2003

Dear Doctor:

This letter is to provide another update of our field experiences with
ProHeart 6 (moxidectin) as we pass the two year anniversary of its
launch, and some label additions being made to reflect some of these
experiences, as noted below. We trust that this information will be
useful and encourage you to call our Professional Services department if
you have any additional questions after reviewing this material.

There are two additions to the ProHeart 6 label that have either been
made, or are in the process of being made. The first was the label
change regarding use of ProHeart 6 in heartworm positive dogs. Briefly,
the changes were made in response to a low number of heartworm-positive
dogs that experienced coughing or cardiopulmonary signs after receiving
ProHeart 6. The pre-approval clinical studies did not identify any such
reactions prior to release, and many heartworm positive dogs have
received ProHeart 6 without side effects. However, based on reports
received on a low number of heartworm positive dogs, Fort Dodge, in
conjunction with the Center for Veterinary Medicine, made the following
changes:

Under the heading "Post Approval Experience," the following statement
was added:

"Cardiopulmonary signs such as coughing and dyspnea may occur in
heartworm-positive dogs treated with ProHeart 6."

Additional labeling changes made under the "Precautions" section of the
package insert and printed cartons in conjunction with this statement
included:

1.  Removal of the statement "At the discretion of the veterinarian"
    before the sentence "Infected dogs should be treated to remove adult
    heartworms."

2.  The following statement was deleted "No adverse reactions were
    observed in dogs with patent heartworm infections when ProHeart 6
    was administered at three times the labeled dose. Higher doses were
    not tested." (A similar statement was already present in the Animal
    Safety section, and this statement was left unchanged.)

The second label change is the recent decision to add a statement
regarding the rare occurrence of death in a low number of dogs treated
with ProHeart 6. Death has been reported in approximately 0.0025 percent
of the doses sold into veterinary clinics. Some of the reports are
associated with severe allergic events, while others appear to be
multifactorial in nature. Some are linked to factors not associated with
product use.

We continue to investigate all reports as fully as possible. If and when
further information becomes available that has clinical implications on
product use, we will advise the veterinary community accordingly.

With regard to the label change, the following new statement, "and rare
reports of death" has been added to the "Post-Approval Experience"
section under the heading "ADVERSE REACTIONS". The full section "Post
Approval Experience" section now reads:

Post-Approval Experience: Although not all adverse events are reported,
the following reactions are based on voluntary post-approval drug
experience reporting: anaphylaxis/toid reactions, depression/lethargy,
urticaria, head/facial edema, and rare reports of death. Anaphylactic
and anaphylactoid reactions should be treated immediately with the same
measures used to treat hypersensitivity reactions to vaccines and other
injectable products. Cardiopulmonary signs such as coughing and dyspnea
may occur in heartworm-positive dogs treated with ProHeart 6.

This revised "Post-Approval Experience" statement will replace the
current wording, which appears in the ProHeart 6 package insert and on
all approved ProHeart 6 printed outer boxes.

In order to help educate your clients on both the benefits and potential
side effects associated with ProHeart 6 (moxidectin), Fort Dodge Animal
Health has prepared a client information sheet which contains questions
and answers about use of the product, and includes the product insert on
the reverse side. An example copy is attached for your reference.
Additional quantities will be available to you through your Fort Dodge
representative and the sheet will soon be posted on our websites for
both veterinarians and clients to download and print.

Thank you for your attention to this important information. We feel it
is essential to provide you with timely updates on the use of this
product. Millions of doses of ProHeart 6 continue to be used safely, and
we trust that this reflects your on-going experience, as well. We
continue our monitoring activities and will provide any pertinent
updates on ProHeart 6 as they become available. Please feel free to
contact one of our Professional Services veterinarians at the number
listed above if you have additional questions or concerns regarding any
of this information.

Sincerely,

Stephen A. Connell, DVM

Vice President,

Professional and Technical Services