Allergan has become the latest Western drugmaker to fall foul of India's intellectual property regime, losing patents on two of its glaucoma products.

The Intellectual Property Appellate Board (IPAB) revoked patents protecting Ganfort (bimatoprost/timolol maleate) and Combigan (brimonidine tartrate/timolol maleate) after a challenge by domestic drugmaker Ajanta Pharma.

Ajanta challenged composition of matter patents covering Ganfort and Combigan in India on the grounds of obviousness, arguing that they did not contain an inventive step and merely covered the combination of two active substances with known activity in glaucoma.

In return, Allergan argued that the formulations used in the two products meant they were more effective than either active ingredient used alone and reduced side effects. The IPAB rejected that assertion and also censured Allergan for allegedly withholding information on patent disputes in other countries.

Glaucoma treatments are a major product category for Allergan, bringing in sales of $540 million out of total company revenues of a little over $3 billion in the first half of this year, with Combigan and Ganfort spearheading growth for the franchise in emerging markets.

The Indian company said in a statement that it has already been selling generic versions of the two products under the Bimat T and Bidin LS brand names for some time, adding it will "continue to [do so] backed by this favourable verdict".

The decision comes shortly after the IPAB revoked a patent protecting GlaxoSmithKline's breast cancer treatment Tykerb (lapatinib), carving two years off its patent life, and another case in which patents protecting Roche's Herceptin (trastuzumab) were withdrawn on procedural grounds.

All told there have been several other cases in which IP held by western companies has been overturned since the start of the year, notably affecting  Novartis' leukaemia drug Glivec (imatinib), Merck & Co's Januvia (sitagliptin) and Singulair (montelukast), Roche's Pegasys (peginterferon alfa-2a), Gilead Sciences' Viread (tenofovir), Pfizer's Sutent (sunitinib) and Bayer's Nexavar (sorafenib tosylate).

Last month, Pfizer's chief intellectual property counsel Roy Waldron told a US Congressional hearing that India was indulging in "protectionist and discriminatory policies" on IP and urged the government to adopt an "equally bold response" to the situation.