WHY IT MATTERS: The Medco acquisition created a PBM large enough to handle the prescriptions of more than one in three Americans.Pharmacy benefits managers run prescription drug plans for employers, insurers and other customers. They process mail-order prescriptions and handle bills for prescriptions filled at retail pharmacies. They use large purchasing power to negotiate lower drug prices and make money by reducing costs for health plan sponsors and members. WHAT'S EXPECTED: Analysts surveyed by FactSet expect, on average, earnings of $1.04 per share on $27.33 billion in revenue. THE 2011 QUARTER: Express Scripts' net income fell 12 percent in the final quarter of 2011, largely on costs tied to the Medco deal. Express Scripts earned $290.4 million, or 59 cents per share, on $12.1 billion in revenue. Results included charges totaling 14 cents per share related to the Medco deal.