Pozen and AstraZeneca are taking their proposed arthritis pain reliever to a Phase III clinical trial under a revised partnership agreement.

Pozen (Nasdaq: POZN) will receive a $30 million payment immediately from AstraZeneca, a global pharmaceutical firm. The new agreement could be worth as much as $345 million for Pozen.

The companies are working on a compound called PN 400. It combines AstraZeneca’s popular heartburn drug Nexium with the anti-inflammatory drug naproxen.

Pozen has proprietary technology that enables the combination of drugs into one compound. It continues to seek approval for a migraine headache pain reliever in partnership with GlaxoSmithKline.

"Millions of people worldwide suffer from arthritis and we are excited about the prospect of developing and bringing an important new therapy to these patients," said Tony Zook, president and chief executive officer at AstraZeneca.

"PN 400 represents an important product development opportunity for AstraZeneca in line with our commitment to bring additional new pain medicines to market that can make a difference in peoples’ lives,” he added. “We are committed to working with POZEN to develop this innovative product and hope to bring it to market as quickly as possible."

Pozen had been due to receive a $20 million payment under the original agreement signed in August of last year.

Pozen and AstraZeneca plan to file a new drug application with the Food and Drug Administration in the first half of 2009.

Pozen stock closed Thursday at $9.98. Its share price has recovered from a 52-week low of $8.29, which was set on August 16 when the FDA declined to approve the Pozen-GSK migraine drug.

AstraZeneca will pay Pozen an additional $55 million if certain development and regulatory requirements are met.

In July, Pozen said a pilot study for PN 400 “met expectations.”