Pernix Therapeutics Holdings Inc. (NYSE: PTX) will acquire Somaxon Pharmaceuticals Inc. (Nasdaq: SOMX) in a stock-for-stock deal valued at $25 million.

Somaxon, headquartered in Solana Beach, Calif., makes Silenor, a prescription sleep medication for patients with insomnia.

Pernix is a specialty pharmaceutical company based in the Woodlands, Texas that develops generic pharmaceutical products. The company agreed to buy Cypress Pharmaceutical Inc. and Hawthorn Pharmaceuticals Inc. in November for $101 million.