India has revoked a patent for an asthma drug held by US-based Merck following a challenge from local pharmaceutical giant Cipla, marking a new blow to global drug firms in the Indian market. The development is the latest in a string of patent revocations by India and involves interpretation of patent protection rules introduced in 2005 to comply with World Trade Organisation regulations.

The drug produced by Merck & Co, a global health care company, was "not inventive", said the order announced late Tuesday. Schering Corp, later acquired by Merck, had applied for a patent for the asthma drug in 2004 and was granted it in 2011.

Copyright Agence France-Presse, 2012