December, 1998

Dear Healthcare Professional:

Merck & Co., Inc., would like to bring to your attention recent changes to the current Physician's Circular and Patient Product Information for SINGULAIR (Montelukast Sodium) Tablets concerning the description of eosinophilic conditions. SINGULAIR is a selective leukotriene (LTD₄) receptor antagonist that was approved by the FDA in February 1998 for the prophylaxis and chronic treatment of asthma in adults and pediatric patients 6 years of age and older.

As part of our customary postmarketing surveillance, we have become aware of case reports in which patients who were receiving SINGULAIR presented with eosinophilic conditions sometimes consistent with the Churg-Strauss syndrome (CSS). Patients presenting with these conditions had significant asthma histories and were receiving multiple asthma medications, often including systemic corticosteroids. On review some of these cases had features consistent with these conditions present prior to initiation of therapy with SINGULAIR. In most but not all of these cases clinical features associated with CSS occurred or worsened during corticosteroid reduction. A causal association between SINGULAIR and these underlying conditions has not been established.

In order to communicate this important information to health care professionals, the PRECAUTIONS and ADVERSE REACTIONS sections of the Product Circular for SINGULAIR have been revised to include the following:

PRECAUTIONS
Eosinophilic Conditions: In rare cases, patients on therapy with SINGULAIR may present with systemic eosinophilia, sometimes presenting with clinical features of vasculitis consistent with Churg-Strauss syndrome, a condition which is often treated with systemic corticosteroid therapy. These events usually, but not always, have been associated with the reduction of oral corticosteroid therapy. Physicians should be alert to eosinophilia, vasculitic rash, worsening pulmonary symptoms, cardiac complications, and/or neuropathy presenting in their patients. A causal association between SINGULAIR and these underlying conditions has not been established (see ADVERSE REACTIONS).

ADVERSE REACTIONS
In rare cases, patients on therapy with SINGULAIR may present with systemic eosinophilia, sometimes presenting with clinical features of vasculitis consistent with Churg-Strauss syndrome, a condition which is often treated with systemic corticosteroid therapy. These events usually, but not always, have been associated with the reduction of oral corticosteroid therapy. Physicians should be alert to eosinophilia, vasculitic rash, worsening pulmonary symptoms, cardiac complications, and/or neuropathy presenting in their patients. A causal association between SINGULAIR and these underlying conditions has not been established (see PRECAUTIONS, Eosinophilic Conditions).

These changes to the Physician's Circular and Patient Product Information are being made voluntarily, based on reports received during marketed use of SINGULAIR since its approval and its use by over 600,000 patients worldwide.

In order to communicate this information to patients, similar changes in laymen's terms have been incorporated into the Patient Product Information for SINGULAIR.

At Merck, our primary concern remains the safety and well-being of the patients who use our products. You can assist us in this regard by reporting all adverse events involving patients on SINGULAIR to the Merck National Service Center at 1-800-672-6372 or to the FDA MedWatch program by phone at 1-800-FDA-1088, by FAX at 1-800-FDA-0178, or by mail at MedWatch, HF-2, 5600 Fishers Lane, Rockville, MD 20857.

Please take the time to read the revised Physician's Circular and Patient Product Information for SINGULAIR which are enclosed. Questions from health care professionals may be directed to the Merck National Service Center. Thank you very much for your time and attention to this matter.

Louis M. Sherwood, M.D.
Senior Vice President
Medical and Scientific Affairs

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