US regulators have upped the warning over an increased risk of infection in patients taking Wyeth and Amgen’s rheumatoid arthritis blockbuster Enbrel, and have included additional information on tuberculosis.

The companies said that, while the drug’s prescribing information had previously included a bolded warning on the risk of infection, this has now been strengthened to the more serious black-box type, with new information added on screening and monitoring patients for TB, including those who have tested negative for latent infection.

Enbrel (etanercept) is a tumour necrosis factor (TNF) inhibitor that works by blocking the body’s production of the inflammatory protein TNF, which is found in excess in patients with an immune disease such as rheumatoid arthritis, ankylosing spondylitis or psoriasis. However, although cutting the amount of TNF in the body will help treat such diseases, it can also impact on the power of the immune system, thereby leaving patients taking the drug more susceptible to infections.

Serious infections such as TB have been recorded in patients taking Enbrel, and the drug’s prescribing information has now also been updated with the incidence of infection reported in clinical trials; in global studies involving more than 20,000 participants, TB was observed in approximately 0.01% of patients.

In line with other anti-TNF therapies
The groups stress that the boxed warning is similar to labeling for other therapies in the TNF inhibitor class of drugs, and that the risks defined “are consistent with the risk of tuberculosis and infections that have been included in previous versions of the US prescribing information”.

Meanwhile, Amgen stock slipped further on news that investment group Moody's is thinking of downgrading its ratings after regulators recommended further restrictions on the firm’s anaemia drugs last week.

The US Food and Drug Administration's Oncologic Drugs Advisory Committee recommended that erythropoiesis-stimulating agents such as Amgen’s Aranesp (darbepoetin alfa) and Epogen (epoetin alfa), plus Johnson & Johnson’s Procrit (also epoetin alfa), should not be used in patients with metastatic breast cancer or cancer of the head and neck. Furthermore, the panellists voted 11 to two that the anaemia drugs should not be used in patients with cancer who have a curative disease.

Shares in Amgen closed down 3% yesterday at $43.08.