Medco Health Solutions Inc. said Tuesday it will compare the blood thinner Plavix, the world's second-best selling drug, with Effient, a potential blockbuster drug sold by Indianapolis-based Eli Lilly and Co.

Medco's proposed study, which would take more than two years, will exclude patients with a genetic mutation that reduces the effectiveness of Plavix and other drugs. Plavix is less expensive than Effient and will be vulnerable to low-cost generic competition in late 2011, and Medco said customers could save money if the study shows Plavix is more effective.

Plavix is sold by Bristol-Myers Squibb Co. of New York and French drugmaker Sanofi-Aventis. About 25 percent of people cannot metabolize Plavix effectively due to a genetic mutation, and Medco plans to exclude those patients from its study. It said genes do not have as much of an effect on Effient.

Franklin Lakes, N.J.-based Medco is a pharmacy benefits manager, and handles benefits for plan operators and members. For Medco, sales of generic drugs are more profitable than higher priced brand-name products.

Medco operates an automated pharmacy and distribution center in Whitestown, and it plans to employ more than 1,400 people there by 2012. The company studies drug data, genetic testing and medical-claims data at the facility.

The  company plans to test Plavix and Effient on more than 14,000 patents with acute heart disease, and evaluate rates of death due to heart problems, heart attacks, and stroke over a six month period. It plans to begin enrolling patients this fall. The study will end in mid-2011 and data will be presented early in 2012, Medco said.