Three members of the US Congress have asked for close oversight of Express Script's $29.1 billion takeover of fellow pharmacy benefit manager Medco Health Solutions to make sure that consumers will not be at risk of rising drug costs.

If the deal goes through, Express Scripts will become the largest PBM in the USA with a customer base of around 135 million, well ahead of next biggest rival CVS Caremark which serves around 85 million people.

Representatives Henry Waxman, Frank Pallone and Diana DeGette have sent a letter to the Federal Trade Commission Chairman Jon Leibowitz urging a "thorough examination" of the merger, which was first announced last month and is scheduled to close in the first half of next year.

"If combined, the newly merged PBMs would control one-third of total 2011 PBM market share and 60% of the market share for mail-order drugs… changing a market with 'three equal competitors' into one with 'one huge player and a distant second and third', says the letter.

The National Community Pharmacists Association (NCPA) also has qualms about the takeover, telling a House subcommittee on Friday last week that consolidation has pervaded the PBM market in recent years and generally resulted in "higher drug costs, decreased patient access to pharmaceutical care and lower quality of care."

It contends that consolidation has made it difficult for patients and health plan sponsors to shop around for deals.

The NCPA has urged support for two legislative proposals currently in the offing, including one bill (H.R. 1946) which would allow independent community pharmacies to band together in contract negotiations with PBM, and another (H.R. 1971/S. 1058) which would introduce consumer protections to help ensure that pharmacy benefit dollars are spent wisely.

The House Judiciary Committee is rumoured to be planning a hearing on the merger on September 20, according to a report on