Revenues at Britvic Ireland fell in the quarter to September 30th, despite a rise in total revenue for the group.
The company blamed "the extremely challenging macro-economic environment", saying the soft drinks market showed no sign of a return to growth in the short term.
"Continuing weakness in the convenience and impulse, and licensed on-premise markets, with volumes down by 1.7 per cent and 20.5 per cent in the 12 weeks respectively, has adversely impacted our business," the company said in a statement.
"The ongoing adverse performance of these channels has contributed to Britvic Ireland's expected volume decline of 13.9 per cent in the quarter to the end of September, and a euro-revenue decline of 16.3 per cent."
In the same period, sterling-based Irish revenues were down 9 per cent, and full-year revenue declined 5.6 per cent.
This is in contrast to a rise in full-year revenue for the drinks group in 2009 of 5.6 per cent to £978.8 million.
The rise in group revenue reflects growth in Britvic's GB carbonates division of 11 per cent, 5.7 per cent growth in the GB stills sector and international growth of 18.5 per cent.
On a quarterly basis, total revenues rose 4.2 per cent year on year to £246.5 million for the 12 weeks to September 27th, 2009, driven by increases in both volume and average realised price.
Chief executive Paul Moody said a "re-engineered business" in Ireland would be well placed to exploit market growth as it returns.
"Strong revenue growth achieved by selling more branded soft drinks at higher prices characterises our performance in the latest quarter and the full year. Compelling brand-equity programmes and strong innovation, supported by excellent execution at the point of sale, have been instrumental in our success," he said.
"The combination of top-line growth and close management of costs mean that we will meet our recently-increased expectations for 2009. Additionally, despite the poor visibility of future market performance, we remain fully confident at this early stage that we have the momentum, brands and in-market execution to deliver another strong set of results for the year ahead."