LONDON, May 12 (Reuters) - Private equity firm Clayton, Dubilier & Rice (CD&R) has agreed to buy London-listed UDG Healthcare for 2.6 billion pounds ($3.7 billion), the pharmaceuticals services company said on Wednesday.

CD&R will pay 10.23 pounds in cash per share in UDG, representing a premium of 21.5% to Tuesday's close. By 0735 GMT the London-listed shares were up 22.2% at 10.30 pounds.

UDG, which has its headquarters in Dublin, specialises in healthcare advisory, communications, commercial, clinical and packaging services.

"We believe that this is an attractive offer for UDG shareholders, which secures the delivery of future value for shareholders in cash today," UDG Chairman Shane Cooke said in a statement.

UDG has two divisions - Ashfield and Sharp - and employs about 9,000 people in 29 countries.

"UDG has long established itself as a leading provider of high-value services to pharma and biotech companies globally, supported by a highly skilled workforce," said CD&R partner Eric Rouzier.

The deal is expected to be declared effective during the third quarter of 2021, subject to shareholder and regulatory approvals.

UDG also reported half-year results to the end of March, showing adjusted pretax profit up 10% at $82.4 million on revenue down 5% at $661.4 million. ($1 = 0.7074 pounds) (Editing by Louise Heavens and David Goodman)