Thousand Oaks biotech giant Amgen's summer doldrums are stretching into the fall, the Los Angeles Times reports.

This month Aetna Inc., one of the nation's largest insurers, quietly changed its reimbursement guidelines for the company's anemia drugs, echoing Medicare's new tighter reimbursement policy for the medicines.

Aetna is the largest private insurer to do so, and analysts expect others to follow soon. That could seriously harm the company's financial outlook because payments by private insurers account for half of the company's sales among cancer patients.

"Aetna is likely to be the first of many insurers to change their guidelines," said Bear, Stearns & Co. biotech analyst Mark Schoenebaum.

The drugs, which are sold by Amgen under the brand names Aranesp and Epogen, treat anemia by boosting red blood cell production and raising hemoglobin levels. A similar product, Procrit, is manufactured by Amgen but sold by Johnson & Johnson. More than 1 million cancer and dialysis patients in the U.S. took the drugs last year.

Recent studies have raised concerns that the drugs may be harmful in some patients and at higher dosages.

People without anemia normally have hemoglobin levels of 13 to 18 grams per deciliter of blood. Research has shown that using drugs to keep anemic patients' hemoglobin levels around 10 grams per deciliter enables the blood to carry enough oxygen for the patient to avoid a transfusion.

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