Millions of patients being transferred to cheaper generic versions of statin drugs may suffer a greater risk of heart attacks and strokes, a study says.

Patients in Britain who have been prescribed branded statins such as Lipitor or Crestor are being switched by their GPs to a cheaper drug, simvastatin, to save money.

The claim is that simvastatin is similar in its effects to Lipitor, the market leader in branded statins, so that nobody will suffer by the switch and the NHS will save tens of millions of pounds a year.

Pfizer, which makes Lipitor, investigated whether such switches were really risk-free by using an NHS data-base compiled from GP data.

It reported yesterday at the European Society of Cardiology Congress in Vienna that patients switched from Lipitor to simvastatin had a 43 per cent higher chance of a major cardiovascular event, such as a heart attack.

Overall risk of death was not increased, but heart attacks increased by 36 per cent and the risk of a stroke more than doubled.

Pfizer’s researchers also found that many people gave up taking the tablets after they were switched, although this could not account for the increase in heart attacks and strokes, which were counted only in people who continued to take their drugs.

Berkeley Phillips, cardiovascular medical manager at Pfizer, emphasised that this was an observational study, useful for forming a hypothesis but not for proving it. “All we can say is that there is an association between switching statins and the effects observed,” he said. “We can’t say it is cause and effect.”

One possible explanation, he said, was that statins are actually different in their effects. The sample, of 2,511 people who had been switched, did not show any difference in the level of “bad” LDL cholesterol, but relatively few GPs had recorded the data.

“We only have that data for 15 per cent of the sample,” Dr Phillips said. “Maybe if we had more it would show that switching leads to higher LDL levels, which could help explain the findings.”

Previous head-to-head comparisons of statins had shown that the choice of drug had little effect on death rates, he said, except in very high-risk patients.

The differences tended to be seen in morbidity, he said: how ill people were and how well their symptoms were controlled.

The Department of Health, which is actively promoting the switch to cheaper drugs, said: “Though it is possible to make significant savings by using generic statins, switching would not be done in cases where it might compromise clinical efficacy or patient safety.

“If patients do not respond positively to one statin, their GP should be free to prescribe another which suits them better, including higher strength branded drugs.

“It is important to note that this is an observational study. While the analysis is interesting it raises many unanswered questions, such as why people were switched from one drug to another, the reasons why compliance with medication was different between the two groups, and the dosages in question. It would be a mistake to draw firm conclusions at this stage.”

But Dr Phillips said that the findings “raised concerns for policies that encourage widespread statin switching without careful clinical assessment of individual patients”.

The study has been accepted for publication in the British Journal of Cardiology.“I hope it will raise a lot of interest and that other countries might want to take a look at their own data-bases and see if the effects are the same,” Dr Phillips said.

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