Is it too late to buy rapid risers ARM Holdings plc, WPP plc ord 10p and Hikma Pharmaceuticals plc?

After the market-wide Brexit carnage on the morning of 24 June, I've been quite surprised by the rapid rebounds in many FTSE 100 stocks. Today I'm looking at three popular UK growth companies and examining whether it's too late to jump on board these gravity defying stocks.

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Tech king

After trading as low as 970p on 24 June, ARM Holdings(LSE: ARM) has spiked to 1,200p, a 24% gain. At that price ARM is trading on a current P/E ratio of 49, which falls to 33 on next year's earnings. Is that too much to pay?

While a P/E ratio of 49 might seem high, on a relative basis it's actually low for ARM. The tech giant has traditionally traded on high multiples thanks to its impressive growth record, with its P/E ratio climbing as high as 143 in early 2014 and averaging 59 over the last 10 years on a quarterly basis.

While analysts have concerns over slowing smartphone growth, I believe the long term growth story is still intact at ARM. The company is broadening its revenue base to focus on networking, servers and the Internet of Things and these areas should offset any weakness in smartphone chip revenues.

ARM has grown its earnings at an annualised rate of 29% over the last five years and with the city forecasting revenue growth of 20% and 13% for the next two years, long term investors should continue to be rewarded.

Blue sky territory

Advertising giant WPP (LSE: WPP) has rebounded 13% since its post Brexit lows and is now trading in blue sky territory, having surpassed its all-time highs set in April.

As advertising companies are often seen as proxies for global growth, I wasn't expecting to see such a rise from WPP with the current economic uncertainty surrounding the UK and Europe. However WPP has strong exposure to the US and fast growing emerging markets, and this has clearly appealed to investors.

As a WPP shareholder I'm not complaining about the stock's recent performance as the company has been one of the better performers in my portfolio since I bought it, showing gains of almost 30% in less than a year. But would I buy more WPP shares at the current price?

Trading on a P/E ratio of 15 times next year's earnings, WPP doesn't look particularly expensive, however looking at the share price chart it's clear to see that it's prone to peaks and troughs. For this reason, I'll be waiting for another dip in the share price before I add to my position.

Fast gains

Hikma Pharmaceuticals(LSE: HIK) has been on my watch list for a while now and I'm kicking myself that I didn't buy a small position during the Brexit chaos as the stock has risen an incredible 38% since then.

I'm very bullish on the long-term prospects for Hikma as after acquiring Bedford Laboratories and Roxane Laboratories in the last two years, the healthcare company is poised to launch many new drugs in the near future. Furthermore, with a high proportion of its sales in the US, Hikma should benefit from weaker sterling.

However, as with WPP, I'll be waiting for a pullback before buying-in. Patience is everything in this game and I'm sure there will be a better opportunity to buy Hikma in the future at a lower price.

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Edward Sheldon owns shares in WPP. The Motley Fool UK has recommended ARM Holdings and Hikma Pharmaceuticals. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.