The stock dropped 185p to 9435p in lunchtime trading after the Irish bookie said group operating profits rose 10% to €180mln on a 24% increase in revenue to €1.1bn.
The merger, which was finalised last month, created one of the world's largest online betting and gaming companies.
On a proforma basis the enlarged group had £1.32bn of revenues and £229mln of underlying operating profits in the year to December 31. Online business contributed 80% of group revenues and 87% of operating profits.
PPB said it would need to cut jobs to remove some duplicated roles from its 7,000-strong workforce in the enlarged company, but did not say how many.
Chief executive Breon Corcoran said the new financial year had begun well, adding: "We continue to operate in a highly competitive industry. We are excited however, by the opportunity to enhance our competitive position."
The group said it benefited from double-digit growth across all its online and retail divisions. It boosted its full-year dividend by 18% to 180 cents per share.
Online revenue lifted 23% and online operating profit rose 11% to €152mln. UK retail revenue put on 15% and 6% on a like-for-like basis while operating profit increased 12% to €23mln.