GlaxoSmithKline (GSK), Europe’s biggest drugs maker, suffered a fresh blow yesterday when American regulators delayed approval of the firm’s cervical cancer vaccine.

The British company said that after the review of Cervarix by the US Food and Drug Administration (FDA), it had asked GSK to answer further questions about the drug.

Analysts said this is likely to delay the drug’s launch in the US market by at least six months.

It is the latest in a series of setbacks for the world’s second-largest pharmaceutical company. Earlier this year sales of its diabetes drug Avandia plummeted by about 50 per cent after reports linking it to heart attacks.

GSK is also facing competition from cheaper generic versions of its products, including Paxil and Wellbutrin, for depression, and needs to bring new drugs to the market.

GSK had seen Cervarix as a key component in its pipeline of new drugs. Analysts had been banking on it generating billions of dollars in sales.

Assuming a six-month delay, analysts at investment bank Panmure Gordon said the setback could knock up to 4 per cent from GSK’s earnings estimates for 2008 to 2010.

Rival vaccine Gardasil, produced by Merck, is already available in America.

In January, GSK announced a head-to-head study of cervical cancer vaccines, pitting Cervarix directly against Merck’s offering.

But Gardasil has been available on the lucrative American market since last year and produced third-quarter sales of $418 million (£207 million).

Cervarix gained EU approval in September and is licensed in a total of 45 countries worldwide, but America represents the largest slice of an estimated $2 billion market for cervical cancer vaccines.

The FDA’s response on Cervarix reflects a general trend among regulators, which have become more cautious in the past few years, demanding more information and licensing fewer drugs.

Peter Cartwright, an analyst at Evolution Securities in London, said: “Cumulatively this is not good for GSK as Cervarix is slated to be a good product. The danger is that Merck will get more entrenched.”

Both Cervarix and Gardasil protect against cancer-causing strains of the sexually transmitted human papillo-mavirus (HPV) and are specifically designed to be given to girls and to young women.

Gardasil targets four strains of HPV - two responsible for cervical cancer and two causing the less serious condition of genital warts - while Cervarix addresses only the two cancer strains.

HPV is widespread, with 80 per cent of women in the US contracting some form of it by the age of 50. About 280,000 women worldwide die of cervical cancer each year, according to World Health Organisation figures, making it the second most common cancer among women after breast cancer.

At the end of October the UK Government announced a £100 million project to vaccinate girls aged 12 to 13 against HPV. The vaccine, which will not be compulsory, costs about £300 for a full course.

GSK’s shares closed down 29p or 2.04 per cent at £12.94, while Merck gained 1.2 per cent to $60.27, in the mid-morning US trade. On a more positive note, GSK announced clinical trial results on Sunday that show a combination of Tyverb - marketed as Tykerb in the US - and Roche’s drug Xeloda, can help to fight breast cancer that has spread to the brain.

History of ailments

2007 GSK faces competition from cheaper generic versions of its products, including Paxil and Wellbutrin, for depression

May 2007 Jean-Pierre Garnier, the chief executive, says that he will retire in May 2008. Andrew Witty, president of the European pharmaceuticals division, will replace him

October 2007 Avandia diabetes pill loses more than half of US sales after a report links it to heart attacks. GSK was forced to print larger warnings on the packets

December 2007 It emerges that David Stout, GSK’s global head of pharmaceuticals, will depart in February after he was overlooked for the chief executive role

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