Merck on Wednesday posted a significant fourth-quarter net loss, reflecting the widespread legal challenges and litigation environment for the US drugmaker and its industry peers.

The magnitude of the loss, weaker-than-expected sales increases in key products, and uncertainty over important cholesterol drugs sales this year, in the face of the US patent expiry of its drug Fosamax, combined to unnerve investors. Merck’s shares fell 3 per cent to $46.69 in New York trading.