I love picking up bargain FTSE 100 shares after they’ve suffered a short, sharp sell-off. Two stocks on my watchlist are now in that exact position. Should I buy them?

The first is pharmaceuticals giant AstraZeneca (LSE: AZN). I’ve been desperate to buy its shares for yonks, but decided they were too expensive after repeated long-term outperformance.

Suddenly, and to my surprise, the AstraZeneca share price is down 11.88% in the last month. So what sparked the sell-off?

What’s gone wrong?

The shares boomed for years as CEO Pascal Soriot successfully replenished the company’s drugs pipeline. However, in September, it’s suffered a couple of setbacks as a new lung cancer and breast cancer treatment both underwhelmed. The results overshadowed successes elsewhere, including US approval for its Fasenra inflammatory disease drug.

Pharmaceutical companies will always have their share of successes and failures, but a long-term investor like me can look past them.

What I’m still struggling to look past is that the shares trade at 35.01 times earnings, well above the average FTSE 100 valuation of around 15.3 times. According to its discounted cash flow (DCF) ratio, they’re overvalued by 7%.

I won’t quibble too much about the relatively low 2.03% yield, that’s largely down to the booming share price. The stock’s up just 5.6% over one year, but almost 60% over five years.

There’s so much to like about AstraZeneca, including gross margins of 75.69%, and a 16.83% return on equity. But it isn’t a blinding bargain, so I’ll wait to see if it gets a bit cheaper.

Housebuilder Barratt Developments (LSE: BDEV) has also had a rocky month, its shares falling 10.35%. Over one year, they’re up just 5.98%.

So what’s up with Barratt? Isn’t the sector supposed to be booming in anticipation of falling interest rates and Labour’s house-building spree?

Barratt is also heading south

Barratt’s gearing up for that by forming a master developer platform with UK government agency Homes England and Lloyds Bank, which will focus on large building sites.

That’s all in the future though. On 4 September, Barratt reported a 75% plunge in full-year profits from £705m to just £170.5m. It pinned that on cost-of-living pressures, higher mortgage rates and low consumer confidence. Completions fell 18.6% to 14,000, although this was at the upper end of expectations. It’ll build even fewer homes in 2025.

Now here’s the killer. It halved the annual dividend to just 16.2p a share. Adding to the uncertainty, it’s pressing ahead on with its £2.5bn takeover of rival Redrow, despite competition concerns.

Given the problems, I’d hoped Barratt’s shares would be cheaper. Today’s trailing P/E of 17.48 times earnings doesn’t blow me away. And while the trailing yield’s a blockbuster 6.89%, it’s forecast to fall to just 3.21% next year.

I’m also worried that Labour will struggle to turn its housebuilding dream into a reality. So I won’t buy Barratt either. I can see much better value elsewhere on today’s FTSE 100.