Shares in Swiss drugmaker Actelion fell more than 5% yesterday after it altered the labelling of its pulmonary arterial hypertension drug Tracleer and sent out a letter to doctors providing new information on the risk of liver damage with the product.

Analysts said the effect on the shares was overblown, as it is already known that Tracleer (bosentan) can cause liver damage and regular monthly liver function checks are already recommended in the labelling for the product. Investors may be sensitive to negative newsflow on the product, which is facing increased competition following the approval of rival PAH drug Revatio (sildenafil) from Pfizer last year.

Tracleer is Actelion’s biggest-selling product, bringing in nearly $500 million in sales in 2005, up 41% over 2004.

Actelion’s shares closed at 108.1 Swiss francs yesterday, but had recovered with interest in mid-morning trading, up more than 6% to 114.2 francs.