Dutch court case to test patent on Glaxo's Advair

* Nov. 26 Hague case pits Glaxo against Novartis unit Sandoz

* Patents previously overturned in Germany, Britain, Ireland

* Generic firms face difficulties copying complex product

By Ben Hirschler and Greg Roumeliotis

LONDON/AMSTERDAM, Nov 25 (Reuters) - GlaxoSmithKline (GSK.L) will seek to defend the patent on its top-selling lung drug Advair in a Dutch court on Friday in the latest in a series of legal skirmishes across Europe over the inhaled medicine.

Earlier patent defeats in Germany, Britain and Ireland suggest its lawyers face an uphill battle. But even if the patent is overturned, it is far from clear how quickly or easily generic firms could launch a cheap copy of the complex product.

The latest case -- between Glaxo and Sandoz, a division of Novartis (NOVN.VX) -- will be heard in the district court of The Hague, a court spokeswoman said. She could not say when a verdict would be delivered, though European courts often hand down decisions several weeks after a hearing.

Advair, or Seretide as it is known in most of Europe, is a key product for Glaxo, selling 5 billion pounds ($7.9 billion) last year and accounting for 18 percent of group revenues.

Despite the generic threat, overall confidence in Advair has actually increased recently after Teva Pharmaceutical Industries (TEVA.O) said it was no longer seeking to develop a copy that would be "substitutable" for the original in the all-important U.S. market. [ID:nLDE6A415H]

Substitutable generics, which can be dispensed by pharmacies even when a prescription is written for the original brand, are far more likely to win market share than non-substitutable ones.

In Europe, though, the hurdles for a substitutable inhaled drug are lower, and Teva plans to file for regulatory approval in 2012. Some analysts think Sandoz could be even closer to launching a copycat version in Europe, after its partner Vectura (VEC.L) disclosed orders for a first batch of inhaler devices last week. [ID:nLDE6AF0WM]

Glaxo Chief Executive Andrew Witty has long argued that Advair will remain a major product, despite losing U.S. patent protection in 2011, because of the technical difficulties of making inhaled drugs.

A lack of generic competition would certainly be a boon for Glaxo as it seeks to gradually move patients from Advair to a new treatment for asthma and chronic obstructive pulmonary disease (COPD) being developed with Theravance (THRX.O).

Glaxo recently gave a promising glimpse of its once-daily successor to Advair, called Relovair, which it expects to be the first next-generation combination respiratory medicine to reach the market. [ID:nLDE68L1N6] [ID:nLDE69K1SZ] (Editing by Will Waterman) ($1=.6345 Pound)