Merck & Co and partner Schering-Plough were celebrating new labelling for their combination cholesterol-lowering drug Vytorin yesterday that support the claim that it is more effective than a key rival in lowering LDL or ‘bad’ cholesterol.

The updated label includes data from a clinical trial which showed that Vytorin (ezetimibe and simvastatin), sold as Inegy in some markets, was more effective than AstraZeneca’s fast-growing Crestor (rosuvastatin) in lowering LDL cholesterol at all the doses tested.

The data came from a 2,600-patient study which found that Vytorin achieved reductions in LDL cholesterol of between 52% and 61%, compared to 46% to 57% for AstraZeneca’s drug.

The latter company has hit back with data of its own showing that combining Crestor with Merck and S-P’s single-agent Zetia (ezetimibe) cuts LDL cholesterol by 70%, the largest fall ever seen in a clinical trial.

Combined sales of Vytorin and Zetia for the Merck/Schering-Plough Pharmaceuticals joint venture were $2.4 billion last year, twice their 2004 tally, while Crestor brought $1.3 billion into AstraZeneca’s coffers.

Vytorin is a critical product for both Merck and S-P, providing the greatest sales potential of any product in either companies' near-term portfolio.