By midday, shares of the online medical encyclopedia have taken off 8.1% to $43.30.
In its first quarter ending March, management anticipates sales of $130 million to $133 million, above $128.7 million consensus, and full-year revenue of $545 million to $575 million, compared to estimates of $568.03 million.
However, the New York-based business warned of softness in the first quarter.
"The first five weeks of sales activity does not reflect year-on-year growth, which is in contrast to the sales momentum we experienced in the fourth quarter of 2013. This change in sales activity does not appear to be the result of any macro issues within our markets," said CEO David Schlanger in a statement.
"The change could be attributable to various factors, such as the continued shift in some of our customers' budgeting and buying patterns, which makes comparison to prior periods and forecasting more challenging."
If weakness in sales should persist, the company said it would impact the rate of revenue growth in the latter half of this year.
For the fourth quarter, the company expects fourth-quarter revenue between $145.5 million and $146.5 million, compared to Thomson Reuters' expectations of $144.43 million, and around 10% higher than the year-ago quarter. Per-share earnings between 23 cents and 25 cents came in above consensus of 18 cents a share.
The board approved an increase of $50 million to the existing stock repurchase program. The amount currently available for buybacks totals $70 million.