One of the most outstanding performers on the the S&P/ASX 200 (Index: ^AXJO) (ASX: XJO) in the last 12 months with a 76% gain has been the fantastic Mayne Pharma Group Ltd (ASX: MYX).

The market has been increasingly bullish on the growing Australian pharmaceutical company since it announced the US$652 million acquisition of a portfolio of drugs from industry giants Teva Pharmaceuticals and Allergan.

The blockbuster deal that closed earlier this month saw Mayne Pharma acquire 37 approved and five FDA filed products for less than 6x forecast FY 2017 EBITDA (that is, earnings before interest, taxes, depreciation and amortisation for the 2017 financial year). According to management the transaction is expected to launch the company into the top 25 retail generic pharmaceutical companies in the United States.

With these deals expected to be significantly accretive to earnings in FY 2017, Mayne Pharma’s shareholders certainly have a lot to look forward to. Especially when you consider that the company has just reported a stunning FY 2016 result this morning that excludes the benefits of these acquisitions.

On the top line Mayne Pharma posted an 89% rise in full year revenue to $267.3 million. While that was undoubtedly strong, it will be the bottom line performance that steals the headlines. For FY 2016 the company reported a stunning 379% jump in net profit to $37.4 million.

The great result was driven by strong performances in all of Mayne Pharma’s divisions, but most notably in its Generic Products Division. This segment’s sales rose 84% to $106.8 million thanks partly to the launch of the BAC tablet and dofetilide products, as well as further market penetration by its oxycodone, hydrocodone, and methamphetamine products.

Net operating cash flow came in 139% higher year on year at $53.5 million after including $26.5 million of tax payments, a $6.7 million one-off settlement payment with a former distributor, and $8.1 million for transactions and other one-off costs.

With earnings per share coming in 302% higher at 4.6 cents, Mayne Pharma’s shares are changing hands at approximately 42x full year earnings. Whilst this might seem expensive, I believe its explosive earnings growth potential more than justifies the premium.

In my opinion Mayne Pharma is right up there with the likes of fellow healthcare shares CSL Limited (ASX: CSL) and Ramsay Health Care Limited (ASX: RHC) as fantastic long-term buy and hold investments.

Finally, before making an investment in Mayne Pharma or any other share I would highly recommend taking a look to see if you own either of these three wealth-destroying ASX shares. Each could be harming your portfolio right now and might be best swapped out.

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Motley Fool contributor James Mickleboro has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.