Comparing year-over-year results for Mylan (NYSE:MYL) will continue to be complicated for the next year and a half or so. Last year, the company acquired Indian generic drugmaker Matrix, and later this year it will complete its acquisition of Merck's generic drug business.

Net revenue rose 56% for the first quarter to $542.7 million. Subtracting the $91 million in revenue generated by Matrix, the old Mylan sill grew revenue by an impressive 30% over the same quarter last year.

Much of that growth was due to $84 million in sales of its generic version of Pfizer's (NYSE:PFE) blood pressure medication Norvasc, which it started selling in March. The large volume of sales won't last because Pfizer delisted its patent on Norvasc in June, opening the floodgates of competition. In fact, there are already 15 competitors on the market pushing down the price.

Another new product is faring much better: the generic version of Ditropan, a medication for overactive bladder made by Johnson & Johnson (NYSE:JNJ) subsidiary Ortho-McNeil Pharmaceutical. The exclusivity period ended May 9, but because the drug has an intricate manufacturing protocol, only one other company's product has made it onto the market.

The Matrix acquisition has done more for Mylan than just give it a presence in India to compete against Dr. Reddy's Laboratories (NYSE:RDY) and Ranbaxy Labs for generic drug sales. First, the acquisition has increased gross margins because Mylan has moved some of its manufacturing to India, where the labor costs are lower. Secondly, the acquisition has expanded Mylan's production capacity; Mylan expects to file 60 abbreviated New Drug Applications (aNDAs) this fiscal year, compared with 24 aNDAs last year.

In Merck's generic drug business, Mylan is swallowing a company one and a half times as large as it is. It's financing the acquisition by taking on a huge amount of debt. After the merger is finalized in October, the company will make a substantial equity offering to generate cash to pay off some of the debt. Mylan will be so much larger than it is now that the increased number of shares shouldn't affect EPS too much. Mylan will need to balance its desire to pay off debt with shareholders' desire to not decrease their equity too much by offering too many shares. Investors will either need to trust that management will strike the right balance, or they should sit on the sidelines and wait to see what the new larger-than-life Mylan looks like on the other side of the merger.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Pfizer is an Inside Value recommendation and Johnson & Johnson was picked by the Income Investor team. The Fool's disclosure policy ensures that you know all that information.