Enbrel (generic name: etanercept) is used to treat rheumatoid arthritis. The drug has been linked with serious blood reactions and nervous system disorders such as multiple sclerosis, myelitis, optic neuritis, and pancytopenia, including aplastic anemia.

The FDA approved Enbrel on November 2, 1998, as the first of a new class of drugs for rheumatoid arthritis (RA) known as biologic response modifiers. Enbrel is a popular drug used by more than 80,000 RA patients in the United States and rapidly gaining in popularity. Enbrel may be responsible for serious blood reactions and and may stimulate nervous system disorders. Reports of 10 occurrences, half of which were fatal, have prompted the drug's manufacturer, Immunex Corp., to issue a cautionary statement about Enbrel's use.

Immunex has warned that patients using Enbrel have been diagnosed with neurological and hematological disorders. In a letter to healthcare professionals, the company said, "Rare cases of central nervous system disorders such as multiple sclerosis, myelitis, and optic neuritis have been reported in patients with rheumatoid arthritis who have received Enbrel therapy." Furthermore, the letter noted some "rare reports of pancytopenia, including aplastic anemia." Both are significant hematological events.

The report specifically notes 11 cases of nervous system disorders and 10 cases of blood-cell shortages that significantly increase the risk of fatal infections.

In a public statement, the company commented that: "In the majority of these cases, there was a close temporal relationship between the start of treatment with etanercept (Enbrel) and the occurrence of hematological disorders (range two weeks to five months). Since the clinical experience with etanercept is still limited as this product has only recently been marketed, onset after this period cannot be ruled out."