Shares of mid-cap biopharma Questcor Pharmaceuticals (UNKNOWN:QCOR.DL) attempted to keep its rally alive by reporting impressive growth in its fourth-quarter results after the bell this evening.

For the quarter, Questcor -- whose lone FDA-approved products is Acthar Gel, a product with 19 current indications – delivered strong sales growth of 51% to $242.9 million which was almost entirely a result of improved Acthar sales. Questcor notes that 8,100 vials of Acthar were shipped during the fourth-quarter, a 28% improvement over the 6,330 that were shipped during the fourth-quarter last year.

Questcor's CEO Don Bailey specifically pointed out that new paid prescriptions "grew about 30%" from the year-ago quarter with rheumatology-related new paid prescriptions providing the biggest surge. Bailey also mentioned that rheumatology now accounts for close to 30% of Questcor's total business after only three quarters of educating rheumatologists on its drug.

Additional sales strength was witnessed from its nephrotic syndrome segment which delivered paid new prescription growth of 5% year-over-year, as well as its multiple sclerosis relapse segment which saw 9% year-over-year new paid prescription growth.

Profit for the quarter improved an equally impressive 53% to $1.67 per share from $1.09 in the fourth-quarter of 2012.

Questcor's release points out that it repurchased 960,000 shares of its common stock during the quarter at an average price of $55.26 per share, and that its board had declared a $0.30 quarterly dividend. Despite mentioning numerous other indications it may seek for Acthar, Questcor did not issue any forward guidance.

Questcor shares were down near $4 per share, or 5%, in after hours at the time of this writing.