UPDATE 1-Irish court invalidates patent on Glaxo's top drug

* Commercial Court rules Seretide combination patent invalid

* Decision is win for Teva, though other patents still apply

* Glaxo may appeal to protect its top-selling drug

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LONDON, June 26 (Reuters) - An Irish court has ruled that a key patent protecting GlaxoSmithKline's (GSK.L: Quote, Profile, Research) biggest-selling medicine is invalid, the British-based drugmaker said on Friday.

The ruling from the Commercial Court in Dublin is a victory for Teva Pharmaceutical Industries (TEVA.TA: Quote, Profile, Research), whose Ivax unit had challenged the combination patent for Seretide. The patent relates to the combination of the active ingredients salmeterol and fluticasone propionate, and expires in 2013.

Seretide, known as Advair in the United States, raked in global sales last year of 4.1 billion pounds ($6.66 billion) as a treatment for asthma and chronic obstructive pulmonary disease (COPD).

Glaxo said it was studying the judgment and would be exploring the possibility of an appeal to a higher court.