Amgen Inc. is grappling with a potential tax bill exceeding $7 billion as the IRS proposes significant adjustments to their taxable income from 2010 to 2015, causing investor anxiety reflected in a 5.4% drop in share price. Despite these challenges, the biopharmaceutical firm reported strong first-quarter earnings of $4.25 per share and revenue of $6.2 billion, surpassing market expectations. The company aims to consolidate ongoing tax court cases while addressing disputes over profit accounting from its Puerto Rico operations.