AstraZeneca has reported a 12% fall in revenue for the first quarter on the back of falling sales of anti-cholesterol drug Crestor.

The pharmaceutical firm announced revenues of $5.4bn (£4.2bn) for the January to March period, down from revenues of $6.1bn in the same period a year earlier.

AstraZeneca lost exclusive rights to Crestor in the US in July, sparking several copycat versions of the statin to appear in the American market and challenge its dominance.

Crestor accounted for $5bn of AstraZeneca's sales in 2015 — considerably more than any other drug in its portfolio.

The Anglo-Swedish firm said the negative impact of the Crestor patent expiry on sales would recede in the second half of the year.

Its pre-tax profits shrank to $582m in the first quarter from $723m in the same period in 2016.

Emerging markets became the largest sales region for the group during the quarter, accounting for nearly a third of total sales.

"Our good start to the year supported our guidance for 2017," AstraZeneca chief executive Pascal Soriot said.

"The pipeline continued to deliver in what we expect will be a pivotal year for AstraZeneca as we announced important developments, in particular in oncology.

"We anticipate the significant progress of the pipeline to continue, including our immuno-oncology and targeted treatments."

The group said it expected results from its MYSTIC cancer immunotherapy trial in mid-2017.