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Sales and marketing expenses increased $5.1 million, from $11.0 million during the three months ended March 31, 2012, to $16.1 million during the three months ended March 31, 2013. The increase was primarily attributable to $4.0 million in salaries and benefits expenses due to the increase in staffing of the Company's field sales force, the classification of $1.4 million of medical affairs expenses to selling and marketing expenses during the first quarter of 2013, and a $0.2 million increase in consulting expenses, which were partially offset by a $0.5 million decrease in launch-related marketing and commercialization expenses.

General and administrative expenses during the three months ended March 31, 2013 were $5.2 million and remained unchanged compared to the comparable prior year quarter. Increases in facilities costs of $0.1 million and $0.2 million in legal fees associated with intellectual property related matters during the first quarter of 2013 were primarily offset by a $0.3 million reduction in audit fees compared to the prior year.

Interest expense decreased $0.9 million, from $4.5 million during the three months ended March 31, 2012 to $3.6 million during the three months ended March 31, 2013. The decrease in interest expense was primarily attributable to the absence in the current year quarter of debt extinguishment costs on prior debt facilities, partially offset by higher borrowing balances in the current year. In February 2012, the Company incurred approximately $2.5 million in pre-payment and end of loan payments associated with the extinguishment of prior debt facilities.

Income tax benefit increased $0.7 million, from $0.2 million during the three months ended March 31, 2012 to $0.9 million during the three months ended March 31, 2013. The increase in income tax benefit during the first quarter of 2013 was primarily due to a reduction in the Company's deferred tax valuation allowance resulting from a determination that a portion of deferred tax assets associated with deferred revenues from milestone payments would be realized in future years.

Note Regarding Use of Non-GAAP Financial Measures

Horizon provides non-GAAP net income (loss) and net income (loss) per share financial measures that include adjustments to GAAP figures. These adjustments to GAAP exclude non-cash items such as stock compensation and depreciation and amortization, non-cash interest expense, and other non-cash charges. Horizon believes that these non-GAAP financial measures, when considered together with the GAAP figures, can enhance an overall understanding of Horizon's financial performance. The non-GAAP financial measures are included with the intent of providing investors with a more complete understanding of operational results and trends. In addition, these non-GAAP financial measures are among the indicators Horizon's management uses for planning and forecasting purposes and measuring the Company's performance. These non-GAAP financial measures should be considered in addition to, and not as a substitute for, or superior to, financial measures calculated in accordance with GAAP. The non-GAAP financial measures used by the Company may be calculated differently from, and therefore may not be comparable to, non-GAAP financial measures used by other companies. Please refer to the financial statements portion of this press release for a reconciliation of these non-GAAP financial measures to the comparable GAAP financial measures.