The drug, launched last year, could yield annual sales of pounds 500m within three years, analysts say. However, some patients have reported chest pains after taking it.
Chest pains occurred in 3-5 per cent of 10,500 patients in the new study. But tests on 8,500 at or shortly after treatment showed no evidence of ischaemia, a decrease in blood supply to the heart, which can be a warning of a heart attack.
Glaxo officials said they did not know the cause of the chest pain but were exploring non-heart functions such as the lungs.
Didier Cowling, Nomura analyst, said the study did little more than confirm what was already known. It might reassure doctors prescribing the drug.
Glaxo shares fell 14p to 750p in a declining market.Reuse content