Pfizer beat back a challenge from generic drugmakers to a patent that protects its pain medicine Lyrica, its second-best selling drug when a federal judge ruled in its favor on Thursday.

Judge Gregory Sleet of the U.S. District Court in Delaware issued an order preventing the manufacture of generic versions of Lyrica before its patent protection expires in 2018. Some generic drugmakers had hoped to launch their versions as soon as this year.

Industry analyst Mark Schoenebaum of ISI Group said a generic challenge to Lyrica could have cut Pfizer's earnings per share by as much as 17 cents in the next five years.

The generic drugmakers argued they could produce a clinically identical drug using a formulation that was not protected.

Patent rulings are often appealed.

Pfizer reported worldwide first quarter Lyrica sales of $955 million, making it second only to its cholesterol fighter Lipitor, which is fast losing revenue in the face of competition from cheaper generic versions.

U.S. Lyrica sales in the quarter were $395 million.

Lyrica is used to treat fibromyalgia, diabetic nerve pain, post herpetic neuralgia - or pain following a case of shingles - and seizures in adults with epilepsy.

In June, the Food and Drug Administration approved Lyrica as a treatment for nerve pain associated with spinal cord injuries.

The generic companies challenging the Lyrica patent were units of Teva Pharmaceutical Industries of Israel, Lupin and Sun Pharmaceutical Industries of India, U.S.-based Mylan and U.S.-based Watson Pharmaceuticals.