Investors were looking for clarity on Catamaran's contract with Medicare provider HealthSpring, which was acquired by U.S. health insurer Cigna Corp .
The contract, which brought in about a third of Catamaran's 2012 revenue of $9.94 billion, is up for renewal this year.
In a call with analysts, Chief Executive Mark Thierer said the company had "good business relationship" with Cigna but did not provide any details on the renewal of the contract.
"The markets were a little disappointed that there was no resolution around Cigna," said Paradigm Capital analyst Gabriel Leung.
Pharmacy benefit managers such as Catamaran Express Scripts Holding Coand CVS Caremark Corpadminister health plans and drug benefits for employers and run mail-order pharmacies.
The company's first-quarter revenue jumped 88 percent to $3.22 billion but still missed analysts' expectations due to lower-than-expected sales volumes and the exit of some of its health plan customers.
Analysts on average had estimated revenue of $3.51 billion.
"This is a high-multiple stock and sometimes small misses can have a material effect on the stock. We think its way overdone," said analyst Tom Liston of Cantor Fitzgerald.
Shares of the company trade at a multiple of 30.7 to its forward earnings, well above rival Express's multiple of 13.9, according to Thomson Reuters StarMine data.
Catamaran shares were trading down 5 percent at C$53.77 on Thursday on the Toronto Stock Exchange. Its Nasdaq-listed shares fell more than 6 percent.
Catamaran's net income in the quarter rose 95 percent to $51.4 million, or 25 cents per share.
On an adjusted basis, it earned 42 cents per share, topping analysts' average estimate of 40 cents per share.
The company maintained its full-year adjusted profit forecast of $1.81-$1.88 per share. It still expects revenue of $14.2 billion to $14.6 billion for the year.
(Reporting by Krithika Krishnamurthy in Bangalore; Editing by Joyjeet Das and Saumyadeb Chakrabarty)