Novartis $NVS is taking a pretty solid hit today. Shares are falling about 13% in premarket trading, and the reason isn't the economy or a weak quarter, but one failed drug.

The experimental drug del-desiran failed in a Phase 3 clinical trial. Novartis paid around $12 billion last year for Avidity, the company developing it. Analysts had expected the drug could eventually generate over $3 billion annually.

As if that weren't enough, it's already the second major clinical trial failure in a few days.

This is, I think, a nice illustration of what's a bit different about pharmaceutical stocks. A company can spend billions on development or buy an entire biotech, everything can look fine for years, and then one trial result comes in and a large chunk of expected value is gone.

Of course, Novartis as a whole is far from finished and hasn't even changed its outlook for this year. The question is how much to trust other drugs in the pipeline and, above all, the company's acquisition strategy.

Does anyone have Novartis in their portfolio? And will you use this drop to buy?