There are good reasons why investors generally don’t view the massive companies in the FTSE 100 as having high growth prospects. But the 160% rise in the share price of pharma giant Shire (LSE: SHP) over the past five years show that assumption isn’t always correct.

What’s the secret to Shire’s success? Vyvanse. This treatment for ADHD has proved one of the blockbuster drugs of its generation and generated sales of over $1.7bn last year alone.

Of course, patents run out eventually and generics bring down market share and margins, so does the company have another blockbuster waiting in the wings for the next half decade?

The chances are quite good. After a massive shopping spree Shire now has over 40 drugs in clinical trials, many of which focus on treating rare diseases. Major acquisitions, alongside shifting its attention to these low volume but high price treatments, have led management to forecast revenue jumping from $6.1bn last year to a whopping $11bn this fiscal year.

Q2 results suggest this target is achievable as Shire’s organic sales grew 19% year-on-year and total product sales leapt 57% thanks to the addition of Baxalta’s business. If this growth continues, hitting the company’s 2020 target of $20bn in sales doesn’t seem far fetched.

Buying Baxalta and numerous other firms has its drawbacks though. Net debt at quarter end had reached a full $24bn, high enough that rating agencies warned the company to avoid more debt-fuelled acquisitions in order to avoid a downgrade to junk bond status.

Management has listened and called a halt to acquisitions for the time being in order to cut down on debt and focus on its newest assets. With EBITDA margins over 40% and sales growing at a rapid clip, debt of this level should be manageable. Throw in Shire’s high growth prospects and a relatively reasonable 16 times forward P/E and this FTSE 100 giant may warrant a second look for growth investors.

High growth but high debt

As cash increasingly goes the way of the dodo for many consumers, one of the biggest potential winners is payment processor Worldpay Group (LSE: WPG). The former RBS spinout’s latest half-year results saw a 15% increase in the total number of payments processed and a 16% jump in net revenue earned from these transactions year-on-year.

The company is working towards continued revenue growth by plowing earnings into international expansion. Although it’s still early days, this push appears to be paying off as the number of payments processed by its global e-commerce segment rose 33% and net revenue increased 25%.

The downside for investors is that Worldpay is coming out of private equity ownership saddled with a large amount of debt. Net debt at the end of June stood at £1.3bn, roughly three times full-year 2015 underlying EBITDA of £406m. That means interest payments and reinvestment in the business will likely preclude high dividends for the time being.

But for growth investors, Worldpay offers a unique way to gain exposure to the rise of online payments across the world. With shares trading at 25 times forecast 2016 earnings they aren’t exactly cheap. But if the company can continue to grow revenue and earnings by double-digits this valuation may not be ridiculous.

Having only gone public last year, Worldpay doesn't have the track record of the Motley Fool's Top Growth Share, which has increased sales every year since going public in 1997.

The market hasn't ignored this success and shares are up in value over 250% in the past five years. The good news for investors on the outside looking in is that the Fool's top analysts believe the company has the potential to triple again in the coming decade.

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Ian Pierce has no position in any shares mentioned. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.