Shares in pharmaceuticals firm Hikma sank 9% after US regulators delayed approval for a new drug.
Hikma has been developing a generic version of GlaxoSmithKline’s lung drug Advair, but US regulators found “major” issues with its application.
The company said there was now “a low likelihood” that the drug would be approved this year.
Hikma was the biggest faller in the FTSE 100, although the index was barely changed in early trade at 7,385.27.
Mondi was another big faller, down nearly 5% after the South African packaging company reported a fall in profits.
First-quarter operating profits dropped 6% to 252m euros (£212m) as a result of lower selling prices and rising costs.
On the currency markets, the pound was unchanged against the dollar at $1.2938, and fell 0.2% against the euro to 1.1886 euros.