British drugmaker GlaxoSmithKline on Wednesday said its net profit rocketed in the first quarter on a vast exceptional gain following a deal with Swiss peer Novartis.

Earnings after tax surged to £8.089 billion ($12.3 billion, 11.0 billion euros) in the three months to the end of March, compared with £668 million in the same period a year earlier, GSK said in a results statement.

GSK took an exceptional gain of £9.262 billion before tax -- or £7.342 billion after tax -- on the Novartis transaction which completed in the first quarter.

GSK sold its oncology business to Novartis for $16 billion, while buying the Swiss group's vaccines division in return.

The pair also formed a joint venture for consumer health products.