GSK has agreed to pay up to $2.2 billion to settle most lawsuits in US state courts claiming that a discontinued version of the heartburn drug Zantac caused cancer, the company announced on Wednesday.

GSK Plc shares surged after the UK pharma company agreed to pay as much as $2.2 billion to resolve about 80,000 US court cases alleging that its old reflux medication Zantac was contaminated with a suspected carcinogen.

GSK said it expects to take a charge of £1.8 billion ($2.3 billion) in its third-quarter results in relation to the settlements, which will be funded through "existing resources," and said there will be "no changes to GSK's growth agenda or investment plans for R&D as a result."