TRENTON, N.J. - Amgen Inc. is recalling some lots of its blockbuster Epogen and Procrit anemia treatments because the injected drugs may contain glass flakes that could cause blood clots, swelling of veins, immune system reactions and other problems.

The Thousand Oaks, Calif., biotechnology company says the flakes are barely visible in most cases, and they have fielded no complaints or reports about problems that can be directly tied to them. Patients experiencing problems should contact their doctor.

Amgen says the flakes are caused by the interaction of the drug with glass vials over the product's shelf life.

The affected lot numbers and expiration dates can be found on websites for the products, and patients can call 1-800-77-AMGEN to ask questions. Patients harmed by the recalled products, or their doctors, should notify the Food and Drug Administration and either Amgen or Johnson & Johnson's Centocor subsidiary.

This is not the first recall this year over a liquid medicine containing glass particles.

Baxter International announced a recall on May 17 for its genetically engineered Hylenex, a solution for rehydrating sick children. Baxter officials also said bits of glass had peeled off the inside of vials.

Epogen treats anemia in patients with chronic renal failure who are on dialysis. Procrit also treats it for cancer patients on chemotherapy and some HIV-infected patients.

Amgen makes both products at plants in Puerto Rico. It has long had a deal under which Johnson & Johnson sells Procrit in the U.S. The drugs work by stimulating production of oxygen-carrying red blood cells, which reduces anemia and can decrease the need for blood transfusions.

Sales of the products have declined somewhat in recent years because of restrictions by the U.S. Centers for Medicare and Medicaid Services over concerns that higher doses of the drugs can be dangerous. Research has shown the medicines are linked to increased risk of death, heart attack, stroke, life-threatening blood clots and growth of tumors in cancer patients.

Amgen reported $2.6 billion in 2009 sales for Epogen, its No. 2 best-selling drug. Johnson & Johnson posted 2009 sales of $2.2 billion worldwide for Procrit and a similar drug it sells overseas called Eprex.

Shares of Amgen rose 60 cents to $56.32 Friday.