AstraZeneca's shares have taken a bashing this morning after data was published showing that its cholesterol drug Crestor failed to beat Pfizer's Lipitor in a head-to-head study.

The Anglo-Swedish drugmaker announced top-line results from the 1,300-patient SATURN study designed to measure the impact of Crestor (rosuvastatin) 40mg and Lipitor (atorvastatin) 80mg on the progression of atherosclerosis in high-risk patients. The results for the primary efficacy measure, which was change from baseline in percent atheroma volume (PAV) in a segment of the targeted coronary artery demonstrated a numerically greater reduction in favour of Crestor but did not reach statistical significance.

However, for the secondary measure, which was change from baseline in total atheroma volume (TAV) within the targeted coronary artery, Crestor did demonstrate a statistically significant reduction compared with Lipitor. Further data will be presented at the American Heart Association meeting in November.

Overall, this is a disappointing result for AstraZeneca as it does not appear to offer any differentiation to Lipitor in high-risk patients, ahead of generic competition to the latter, starting in the USA on November 30. Crestor is the company's biggest-selling drug (second-quarter turnover was up 20% to $1.71 billion) and better results from SATURN would have probably boosted those figures, but given these results, doctors are likely to plump for soon-to-be available cheap copies of Lipitor.

Analyst Navid Malik at Matrix Group has issued a research note saying that the failure of the study to reach statistical significance "calls into question the rationale for use of the 40mg dose altogether". He added that the result "potentially muddies the water on the data previously seen in the JUPITER study, which resulted in a label change for Crestor".

Mr Malik is waiting to see further data from the study, "in particular related to Crestor’s safety profile at 40mg in these high-risk patients, where previous study in PLANET 1 and PLANET 2 showed trends towards kidney toxicity versus Lipitor". He expects to see downgrades to Crestor sales, adding that he sees AstraZeneca as "unable to offset the generic exposure it faces from patent expirations, ongoing poor delivery from its pipeline and an under-weighting in biological drugs".

Investors are worried too and at 9.00am (UK time), AstraZeneca shares were down 3.3% to £28.20.