Biotechnology shares plunged towards a bear market as losses in one of the year’s best-performing industries snowballed amid concerns about drug prices.

The Nasdaq Biotechnology Index dropped by more than 6 per cent in New York, with declines accelerating in afternoon trading. The gauge slumped 22 per cent from a record in July and is headed for its worst week since 2008.

Investors have been singling out biotech since Democratic presidential hopeful Hillary Clinton on Monday tweeted about possible “price gouging” in the market for prescription pills.

Having surged more than 450 per cent in the six-year bull market, the industry is now finding less favour among investors than its more staid older cousins, which include Aetna Inc and HCA Holdings Inc.