Nastech Pharmaceutical of the USA saw 13% wiped off the value of its shares yesterday after the US Food and Drug Administration rejected its application to market a generic version of Novartis’ osteoporosis treatment Miacalcin.

The FDA turned down Nastech’s version of the nasally-administered drug because it said an interaction between the active ingredient – salmon calcitonin – and a preservative called chlorabutanol used in the formulation could cause allergic reactions.

Nastech said it was seeking a meeting with the FDA to explore the matter further, but was surprised by the verdict as other nasal spray products are on the market using chlorabutanol as a preservative. It also said it saw no evidence of immune reactions in its clinical trials of the product.

If it transpires that Nastech cannot convince the FDA to approved its intranasal salmon calcitonin product as a generic, the company may choose to go down the New Drug Application route, although this is likely to require additional clinical trials.

Miacalcin had sales of $225 million in the USA last year and is still patented in the USA by Novartis until 2015. But Nastech’s formulation is claimed to be dissimilar enough to Miacalcin to bypass the patent, but similar enough to be substitutable for the brand and so classed as a generic.

Nastech first filed for approval of its product in 2003, but approval has been blocked by a Citizen’s Petition asking for more information on its comparability to Miacalcin. A similar tactic was used to block approval of another intranasal salmon calcitonin product, Upsher-Smith’s Fortical, last year.

Nastech is also developing a nasal spray formulation of parathyroid hormone, called PTH1-34, alongside Procter & Gamble. This product is due to be filed for approval in 2007.