When is a drug deemed so 'successful' that it deserves to be pulled off a trial?

There doesn't seem to be a standard rule on this, although apparently independent monitoring boards can make the decision if they see fit. A drug could take up to 10, 15 years or more to complete all 3 phases of its clinical trial, but this time varies depending on factors such as the type of treatment and problems with the new drug.

Is this the best way to ensure the safety and efficacy of drugs, the two most important duties of the MHRA's expert advisory body, the Commission on Human Medicine? A member of the British Pharmacopoeia Commission, who prefers to remain anonymous, had this to say about the recent controversy surrounding Vioxx:

'The adverse reaction with Vioxx only became effective after 18 months and the risk was an increased cardiovascular event. Slightly. A slight but real risk, but this wasn’t showing up if a patient was taking it for 18 months. If a patient was only taking it for 12 months, it only became apparent after 18 months. There's a very fine balance, you have the experts, the scientific experts as employees of the MHRA and those employed on commissions to advise of the work of the MHRA – they only take decisions based on information they receive.'

So why not gather as much information as possible before making a decision that could harm patients? This may have made a difference during the clinical trials for the anti-cholesterol drug Crestor (Rosuvastatin). There have been calls to have it removed from the market due to safety concerns as it carries a higher risk of side effects compared to other statins. But these negative reports have been buried under a barrage of good news. It has now emerged the statin drug trial was halted six months early after being hailed a success.

'The study was funded by the drug company Astra-Zeneca, the maker of the statin used in the trial, Rosuvastatin, marketed under the name Crestor. Astra-Zeneca had no access to unblinded trial data and played no role in the study’s analysis or interpretation, according to Brigham and Women’s Hospital.'