Sales of cheap versions of drugs in the United States have sent profits jumping 139% at India's biggest pharmaceutical business.

Ranbaxy Laboratories is one of a growing number of Indian companies profiting from selling copycat medicines when patents expire.

The company made 6bn rupees ($126m; �78m) last year.

Ranbaxy sells its drugs in more than 70 countries but the US is its biggest market.

"We expect the US to continue to be the major contributor of revenue and remain the growth vehicle for the company," said managing director DS Brar.

New drugs

One of the best performing drugs was a generic version of GlaxoSmithKline's Ceftin antibiotic, which Ranbaxy launched last March.

The drug accounted for nearly 15% of the company's $789m sales.

The firm said that other anti-infective drugs such as Amoxicillin, Cefaclor and Cephalexin also performed well in the US.

Last year Ranbaxy applied for permission to sell 23 new versions of drugs whose patents were expiring in the US.

More competition

The company said it had just launched a generic version of GlaxoSmithKline's blockbuster antibiotic Augmentin in the US.

And it expects to launch a copycat version of Roche's anti-acne drug Accutane in the next two months.

But these drugs are unlikely to perform as well as Ceftin.

Ranbaxy's generic Ceftin was the only version on the market, but the drug maker will face competition from rival firms for sales of Augmentin and Accutane.