Merck & Co and Schering-Plough have temporarily suspended television advertising for their combination cholesterol treatment Vytorin (ezetimibe + simvastatin) in the US, as Vytorin prescriptions and the companies’ share prices buckle under the fall-out from the now notorious ENHANCE trial.

TV advertising for Zetia (ezetimibe) has also been suspended, although print advertising continues for both drugs and the joint venture partners have launched a new print campaign in US newspapers, in which they “proudly stand behind the established efficacy and safety profiles of Zetia and Vytorin”.

Merck/Schering-Plough Pharmaceuticals said the decision to suspend direct-to-consumer (DTC) broadcast advertising for the drugs had been taken in view of “mischaracterisation and misinterpretation” of the ENHANCE results, which showed Vytorin to be no more effective at slowing the progression of atherosclerosis than simvastatin (the now genericised Zocor) alone.

According to research firm TNS Media Intelligence data, the two companies spent around US$102 million on DTC advertising for Vytorin in the first nine months of 2007, and US$83 million on Zetia. The US House Committee on Energy and Commerce, which is aggressively pursuing an investigation of the ENHANCE trial, has asked why “a study showing that Vytorin provides no increased benefit was not issued for nearly two years while direct-to-consumer advertisements were carried on the airways”.

The new print advertisements for Vytorin and Zetia are co-signed by Dr Robert Murray, vice-president for external medical and scientific affairs at Merck & Co, and Dr Robert Spiegel, chief medical officer at Schering-Plough. They note that patients taking Zetia or Vytorin “may be worried about recent news stories questioning the benefit of these medicines … on the basis of a single study that has generated a lot of confusion”.

In fact, the ads continue, Zetia and Vytorin “have been proven to lower LDL (bad) cholesterol along with diet in multiple clinical studies involving thousands of patients. Both the American College of Cardiology and the American Heart Association agree that lowering bad cholesterol is important.”

The damage limitation exercise comes as evidence begins to emerge that sales of Vytorin are wilting under the strain. A Dow Jones report cites data from market research firm Verispan, showing that prescriptions written for Vytorin in the week ended 18 January 2008 fell by around 9.5% to 359,659 from 397,533 in the week ended 11 January. However, the report also mentions a research note from Morgan Stanley, which notes that new prescriptions for Vytorin have been falling but there are “already signs of stabilisation”.

In the meantime, the House Committee on Energy and Commerce has further deepened its investigation into the ENHANCE trial, with the latest requests for information including all records of stock sales by Schering-Plough and Merck corporate officers between April 2006, when the trial ended, and January 2008, when the results were finally released.