US regulators have rejected Schering-Plough and Merck & Co’s bid to get approval for a combination tablet of the firms’ big-selling Claritin and Singulair.

The two companies said they received a not-approvable letter from the US Food and Drug Administration for a proposed fixed combination of S-P’s Claritin (loratadine) and Merck’s Singulair (montelukast) for the treatment of allergic rhinitis symptoms in patients who want relief from nasal congestion.

Neither the agency nor the firms would say whether the drug has been turned down for safety or efficacy issues and the S-P/Merck joint venture limited itself to saying that it is evaluating the FDA's response. When the combo was filed in August last year, S-P noted that the product “provided a consistent and clinically relevant effect on congestion that was not demonstrated with the individual components”.

It was noted that the FDA’s decision will not affect the availability or continued use of either Claritin, which is already off-patent or Singulair, though the agency has just set up a probe into a potential link between the latter drug and suicidial behaviour.

If approved, the hay fever medicine would have been sold through the JV which currently markets the controversial cholesterol-buster Vytorin - a combination of Zetia (ezetimibe) and Merck's statin Zocor (simvastatin).