They may be multibillion-dollar corporations, but the crisis over Avandia illustrates the vulnerability of big pharmaceutical companies to crises of public confidence.

Until last week, GlaxoSmithKline was widely viewed as one of the better-positioned top-tier groups in the world – with a strong pipeline of drugs and less vulnerability to patent expiries on its key products than some of its closest rivals – but a single, widely criticised report that linked one of its top medicines to an increased risk of heart attack has been enough to trigger a £9 billion sell-off in the company’s shares.

Even the report’s author, Steven Nissen, has admitted that further research is needed to establish the truth about Avandia’s safety profile, but there is little doubt that sales will be affected. The question is just how long this lasts and whether public trust can be restored.

The scientific debate is likely to continue for months. America’s Food and Drug Administration (FDA) has reserved judgment so far, but it is expected to issue a report within the next few weeks.

While it is possible that Avandia could be pulled from the market, it is unlikely and more probable that it will carry stronger “black box” warnings on its label to doctors. Avandia is Glaxo’s topselling product after Advair, the asthma drug, generating sales of £1.6 billion last year out of £23.2 billion.

Even before the scandal broke, it was under pressure from new drugs, such as Eli Lilly’s Byetta and Merck’s Januvia.

Part of the problem for Glaxo is that it is being led unwillingly into a political row in Washington over the position and role of the embattled FDA.

For many American politicians, the row over Avandia represents a political weapon in a wider debate on drug safety regulation and the prices charged by big drug companies.

While the future remains highly uncertain for Glaxo at the moment, there are some reasons to be cheerful.

After a 9 per cent increase in sales last year, ten products launching this year and thirty-one in late-stage development, it remains a fundamentally strong business – with or without Avandia.

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