Rapidly growing mid-cap biopharma Jazz Pharmaceuticals (NASDAQ:JAZZ) continued its hot streak of double-digit profit improvements after the closing bell this evening with the release of its fourth-quarter earnings results.

For the quarter, net sales increased 28% to $235.8 million from $183.7 in the year-ago quarter. Narcolepsy drug Xyrem provided the biggest punch with sales soaring 45% during the quarter to $164.2 million. For the year, Xyrem sales jumped 50% to $569.1 million, and accounted for 65% of Jazz's total revenue. Specialized acute lymphoblastic leukemia therapy Erwinaze/Erwinase also delivered notable sales growth of 26% to $43.5 million during the quarter. On the flipside, the company's psychiatry product sales dipped by nearly 50% to $9.1 million during the quarter.

Adjusted profit for the quarter rose 13% to $106.1 million, or $1.72 per share, from the $93.9 million, or $1.53 per share, reported in the year-ago quarter. Profit rose predominantly from increased sales of Xyrem and were partially offset by a nearly $20 million increase in selling, general, and administrative expenses, and a 90% increase in research and development costs.

Also announced concurrently with Jazz's earnings release was the departure of its chief financial officer, Kathryn Falberg, effective March 9, 2014, to pursue other interests. According to the company's press release, Matthew Young has been appointed as the new CFO with Falberg acting as a consultant during the transition period.

Looking toward 2014, Jazz issued full-year revenue guidance of $1.1 billion to $1.16 billion, with net Xyrem sales of $755 million-$775 million, net Erwinaze/Erwinase sales of $185 million-$200 million, and net Defitelio sales (a treatment for severe hepatic vaso-occlusive disease that was acquired when it purchased Gentium) of $42 million-$52 million. To add some context to these figures, this represents year-over-year sales growth of 30% at the midpoint of its topline guidance, and 34% sales growth in Xyrem at the midpoint.

Furthermore, Jazz is forecasting full-year adjusted EPS in a range of $8-$8.25, an approximate 29% improvement at the midpoint over the $6.31 in adjusted EPS reported for the full-year tonight.

Shares of Jazz Pharmaceuticals are down nearly $15, or 9%, in after-hours at the time of this writing.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.