Merck & Co., the second-biggest U.S. drugmaker, agreed to buy Idenix Pharmaceuticals Inc. for about $3.85 billion to expand its experimental pipeline for hepatitis C treatments.

Idenix holders will receive $24.50 a share in cash, Merck said in a statement today. The price is more than triple Idenix’s closing level on June 6 of $7.23. The premium is a record for health-care deals larger than $100 million, according to data compiled by Bloomberg.

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