UPDATE 1-EU approves Novartis' Diovan for paediatric use

* Novartis hypertension drug approved for use in EU children

* Approval opens way for 6-month Diovan patent extension

* Analysts forecast Diovan sales of $6 bln in 2010

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ZURICH, April 23 (Reuters) - Swiss drugmaker Novartis (NOVN.VX) said the European Commission approved Diovan, its biggest selling drug, to treat children and adolescents with high blood pressure, a move likely to extend patent protection.

Novartis said on Friday following the approval and in line with European paediatric regulation, it would apply for a six-month extension to its patent protection for valsartan, Diovan's active ingredient.

The number of children with high blood pressure in the EU is unknown, said Novartis, but data from EU countries suggest the rate could be up to 11 percent, higher than previously thought.

"We are seeing an increasing number of children and adolescents being diagnosed with high blood pressure, a trend largely the result of the growing number of young people who are overweight or obese," said Franz Schaefer, professor of paediatrics at Heidelberg University Hospital, Germany in the Novartis statement.

Diovan is the world's biggest-selling blood pressure drug, with sales expected to reach $6 billion in 2010. [ID:nLDE63C0BC].

Novartis shares traded largely unchanged at 55.95 Swiss francs at 0808 GMT, underperforming a slightly higher European Stoxx 600 healthcare sector index.SXDP (Reporting by Martin de Sa'Pinto, editing by Will Waterman)