Sales and earnings at AstraZeneca (LSE: AZN) have been disappointing in recent years. Could it be time to give the FTSE 100 pharma giant the elbow and look instead to FTSE 250 growth stock BTG (LSE: BTG) or AIM-listed biotech Silence Therapeutics (LSE: SLN)?

Astra versus BTG

AstraZeneca has seen annual earnings declines that have totted up to the extent that 2015 earnings came in some 40% lower than in 2011. And earnings are set for further falls in both the current year and 2017, according to City consensus forecasts.

In contrast, BTG’s earnings have been on the rise, and the consensus forecast yesterday was for an 18% increase for the company’s financial year ending 31 March. That may be revised upwards somewhat, after the company said in a pre-close trading update today that revenue for the year is now expected to be at the upper end of its guidance range, albeit boosted by currency tailwinds.

With BTG reinvesting cash generated from its specialty pharmaceuticals and licensing businesses into its interventional medicine portfolio, analysts expect earnings to accelerate higher in the next two years, with growth of around 20% rocketing to 40%. If the company delivers, a current price-to-earnings (P/E) ratio of well above 30 would fall to around 20.

BTG appears to have a clear routemap for producing strong long-term earnings growth, and the shares could prove to be a good buy at their current 625p level.

However, I believe Astra also offers excellent value right now. The shares are trading at below £40, and the P/E on what is expected to be the bottom of the company’s earnings declines next year is an attractive 14, with a 5% dividend yield to boot.

Despite going through a difficult period, Astra’s medium-to-long-term future is looking bright, which is perhaps recognised by the £55-a-share offer US giant Pfizer made for the company a couple of years ago.

Silence Therapeutics

Silence Therapeutics is a very different proposition to Astra and BTG in that earnings are currently negative. In fact, the company doesn’t even generate any revenue — and the situation isn’t expected to change for a few years yet.

This small biotech firm — it has a market cap of £86m at a current share price of 123p — describes itself as “a leader in the discovery, development and delivery of novel RNA therapeutics for the treatment of serious diseases “.

I always find it irritating when companies use unexplained specialist acronyms, initialisms and other abbreviations in their communications to investors and potential investors. I had to look up RNA, which would seem to be ribonucleic acid, which is apparently important in the coding, decoding, regulation, and expression of genes.

Silence has been burning less than £10m a year cash on developing its pipeline, and with net cash of £52m reported in its annual results today, the company is clearly well-funded. However, putting an appropriate valuation on the business at this stage is not easy. As such, I would be more comfortable investing in Astra and BTG.

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G A Chester has no position in any shares mentioned. The Motley Fool UK has recommended AstraZeneca and BTG. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.