GlaxoSmithKline has increased its stake in American lung drug firm Theravance to 19% after picking up 5.75m shares in a private placing today.The UK drugs giant is paying $22.5 a share for the holding, valuing the deal at $129.4m and taking its total interest in its respiratory drug partner to 15.15m shares.It has been working with Theravance since 2002 when the pair got together to develop a new treatment for asthmas and bronchitis. Relovair is now in Phase III development.Glaxo hopes it will be the one that replaces its blockbuster drug Advair, which racked up sales of £5bn last year."We were keen to take advantage of this opportunity to increase our shareholding in Theravance," Moncef Slaoui, Glaxo's chairman of research & development said Monday."This reflects the confidence we have in the Relovair programme and the wider late stage respiratory pipeline that we have built up through the collaboration."