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WASHINGTON (Reuters Health) – Schering-Plough Corp. said on Monday that it received a supplementary approval from the US Food and Drug Administration (FDA) to market the 5 mg tablet of its new allergy drug Clarinex (desloratadine) for perennial allergic rhinitis.

Clarinex previously was approved for the treatment of seasonal allergies in December. Schering-Plough is now hoping the drug will serve as the successor to its blockbuster allergy treatment Claritin (loratadine), which could face generic competition by December 2002.

Kenilworth, New Jersey-based Schering-Plough said that the supplementary FDA approval earned Clarinex the broadest indications of any non-sedating antihistamine currently on the US market. Other sedating antihistamines already have the same indications.

Schering-Plough said that the FDA approval included indications for chronic idiopathic urticaria (CIU), or hives of unknown cause, a condition that affects an estimated 15% to 25% of Americans at least once in their lifetimes.

The company estimated the incidence of perennial allergic rhinitis, or indoor allergies to such things as dust mites, at 20% to 30% of the American population. The firm said that the combined incidence for seasonal and indoor allergies was an estimated 40% to 50% of the US population, citing data from market research firm Decision Resources Inc.

Schering-Plough said that the supplementary FDA approval was based upon two clinical trials of 1,300 patients, in which the 5 mg dose was shown to provide 24 hours of relief from both nasal and non-nasal symptoms. The company said that the most common side effects included dry mouth and fatigue, but they occurred with the same incidence as placebo.

Although many antihistamines have been shown to interact with grapefruit, the company added that grapefruit was shown in the clinical trials not to affect the absorption of Clarinex, supporting the drug's superior side effect profile. Schering-Plough noted that Clarinex also was shown to have no effect on pulmonary function, allowing for its administration to patients with concomitant conditions such as asthma.

Schering-Plough spokesman William O'Donnell told Reuters Health that the company would now detail that broadened indication to doctors. O'Donnell said that the company would conduct a "significant" education campaign.

Although refusing to comment on patient migrations from Claritin to Clarinex, O'Donnell added that the market reception has been encouraging.

Earlier last week, Schering-Plough announced that it was suing Johnson & Johnson of New Brunswick, New Jersey, and American Home Products of Madison, New Jersey, for filing with the FDA to market a generic version of Claritin as an over-the-counter product.

The companies' announcement preceded a comment by US Secretary of Health and Human Services (HHS) Tommy Thompson that he would support the OTC switch for Allegra, Claritin and New York City-based Pfizer Inc.'s Zyrtec.

Some analysts, though, do not believe such a "forced switch" would be possible. Instead, they believe any possible switch would occur after Claritin lost its patent protection.

In Monday afternoon trading on the New York Stock Exchange, shares of Schering-Plough rose $1.68, or 5.2%, to $33.95.