Teva Pharmaceutical Industries posted lower first-quarter profit as its revenue in the United States was hurt by a drop in sales of a key product due to generic competition.

Teva, the world's biggest maker of generic drugs, earned $1.12 per diluted share excluding one-time items in the quarter, compared with $1.47 a year earlier. Revenue fell to $4.9 billion from $5.1 billion, the Israeli company said on Thursday.

Teva was forecast to earn $1.10 a share excluding items on revenue of $4.85 billion, according to Thomson Reuters I/B/E/S.

Teva is five months into a sweeping reorganization it promised would bring extra rewards for shareholders. The company has grown rapidly in recent years through a series of multibillion-dollar acquisitions but its shares have badly underperformed its rivals in the past two years.

Among its key challenges is the looming 2015 patent expiration of its most important branded product, the multiple sclerosis drug Copaxone, which accounts for about 20 percent of sales and some 50 percent of profit.

Copaxone posted a 17 percent rise in global sales in the quarter to $1.1 billion. The drug, which is injected, faces competition from oral treatments that are already available or expected to hit the market in coming years.

"Our generic operations, which are a core component of our business, performed in line with our expectations and were particularly strong in Western and Eastern Europe," said Jeremy Levin, Teva's chief executive officer.

Teva's U.S. sales, which comprise 50 percent of total sales, fell 11 percent in the first quarter to $2.4 billion as sales of sleep disorder drug Provigil declined substantially due to generic competition that began in the second quarter of 2012.

Teva declared a quarterly dividend of 1.15 shekels (32 cents) a share, unchanged from the fourth quarter when it raised its payout by 15 percent.