UPDATE 1-AbbVie profit beats estimates on surging Humira sales

(Adds details on sales, tax inversions)

July 25 (Reuters) - AbbVie Inc, which last week announced plans to buy Dublin-based drugmaker Shire Plc for $55 billion, reported stronger-than-expected quarterly results on surging sales of its Humira treatment for rheumatoid arthritis.

The U.S. drugmaker said on Friday that it had earned $1.1 billion, or 68 cents per share, in the second quarter. That compared with $1.07 billion, or 66 cents per share, a year earlier, when it took charges for research, separation costs and a restructuring.

Excluding special items, AbbVie earned 82 cents per share. Analysts on average expected 76 cents, according to Thomson Reuters I/B/E/S.

Sales rose 5 percent to $4.93 billion, topping Wall Street expectations of $4.7 billion. AbbVie attributed the growth mainly to Humira, an injectable treatment whose global sales jumped 26 percent to $3.29 billion.

Humira, the world's top-selling drug, now accounts for 67 percent of sales. The company's heavily reliance on the medicine is a main reason AbbVie sought out Shire, which has an array of lucrative treatments for rare diseases.

AbbVie, after buying Shire, plans to locate the combined company to Britain, where taxes are lower. The maneuver, called tax inversion, is being used by many U.S. companies, especially drugmakers, and has come under fire from President Barack Obama and some members of Congress.

(Reporting by Ransdell Pierson; Editing by Jeffrey Benkoe and Lisa Von Ahn)