Generic drugs maker Barr Laboratories yesterday revealed that it has been slapped with a patent infringement lawsuit by fellow US firm Sepracor in relation to the inhalable asthma medicine Xopenex (levalbuterol HCl).

Xopenex is indicated for the treatment or prevention of bronchospasm in adults, adolescents, and children six years of age and older with reversible obstructive airway disease and is one of Sepracor’s biggest products with sales of approximately $609 million in the USA, based on IMS sales data for the twelve months ended May 2007.

In a statement, Barr said it is challenging the patents covering the asthma drug and is seeking Food and Drug Administration approval for a copycat version of Xopenex in the USA; the agency accepted its application in May and it is currently under review. Sepracor has subsequently notified Barr that it has begun proceedings in the US District Court of Delaware to prevent it from marketing its version of Xopenex.

It’s not the only piece of bad news to hit the product recently. Last month, Sepracor revealed that under a new scheme the Centers for Medicare and Medicaid has bundled its Xopenex inhalation solution with generic albuterol, significantly lowering the product’s current reimbursement rate from the beginning of July onwards unless a “better alternative” can be identified and agreed upon with government officials. Sepracor says it has no idea as yet what the impact on revenues will be.