NEW YORK (TheStreet) -- Shares of Pernix Therapeutics  (PTX) - Get Report plunged 17.95% to $8.18 in afternoon trading Thursday after the company updated its full-year 2015 guidance.

The company now expects net sales for the three months ended March 31, 2015, to be in a range of $32 million to $35 million, compared with $19 million in the same period in 2014.

Pernix also expects net sales in the range of $220 million to $240 million for the full year 2015.

The company said results in the quarter were mostly affected by "lower Treximet prescription volume, a reduction in channel inventory related, in part, to the lower prescription volume, adjustments to gross-to-net discounts, and delays in the delivery of Treximet patient samples to our field sales force."

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"We expect Treximet to respond positively to our promotional efforts as the sampling launch commences in full force, similar to the success we achieved in re-launching Silenor," said Doug Drysdale, Chairman and CEO of Pernix, in a statement. 

"With the pending acquisition of the Zohydro ER franchise, we are building a strong portfolio of three strategically promoted brands, each in large markets, with significant growth potential. We are confident in our ability to build value for our shareholders from our current products and future portfolio additions," Drysdale continued.

PTX data by YCharts

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