Shares in Impax Laboratories were on the slide yesterday after the US Food and Drug Administration rejected its Vadova drug for treating Parkinson's disease.

Impax said it was uncertain whether it would ever be able to bring Vadova (carbidopa/levodopa) tablets to market, but would be seeking a meeting with FDA to review its concerns about the product.

The agency’s letter cites several deficiencies in the application, including observations resulting from an FDA inspection of the contract laboratory employed by Impax to perform bioequivalence studies.

"We followed the study design described in our Investigational New Drug application and we believe the results obtained not only present a valuable product for the patient but are within the regulatory requirements," said Impax president Dr Larry Hsu.

Shares in Impax fell nearly 15% on the news, ending the day at $8.76.

Vadova would be a competitor to Bristol-Myers Squibb’s Sinemet and Sinemet CR levocopa/carbidopa products, which lost patent protection in the USA in 2003, and its generic equivalents.

Impax already sells generic versions of these products, but maintains that Vadova provides faster and more sustained levels of the active compounds in the blood.