Amgen’s woes are not over yet. The Thousand Oaks biotech company may see a further withering of profits. Aetna Inc, one of the largest insurers in the nation, has changed its reimbursement guidelines for Amgen’s anemia drugs, the Los Angeles Times reported Friday. That may harm the company financially because payments for private insurers make up half of the company’s sales for cancer patients, the Times reported. Other insurers are expected to follow suit. “Aetna is likely to be the first of many insurers to change their guidelines,” Mark Shoenebaum, analyst for Bear, Stearns & Co., told the Times. The Amgen drugs, called Aranesp and Epogen, treat anemia by raising red blood cell production and hemogoblin levels. This summer, Amgen was hit by a drop in sales when concerns were raised about the drugs potential side effects.