Ipsen's Q3 sales up, launches US neck spasm drug

* Q3 sales up 7.8 pct, drug sales up 9.4 at constant rates

* Dysport launched in U.S. for spasm in neck muscles

* Partner Roche says diabetes drug meets Phase III goal

PARIS, Oct 29 (Reuters) - French drugmaker Ipsen (IPN.PA) reported 7.8 percent growth in its quarterly sales and forecast an operating margin of as much as 17.5 percent of sales this year while announcing the U.S. launch of one of its treatments.

Ipsen announced the launch of its muscle relaxant Dysport to treat spasms of the neck muscles, a disorder that is called cervical dystonia in the world's biggest drug market, making it the group's third product available worldwide.

In addition, Swiss partner Roche (ROG.VX) had found that diabetes candidate drug Taspoglutide, stemming from Ipsen's laboratories, met its primary endpoint or key goal in a final phase clinical trial, Ipsen said.

Group sales in the third quarter rose 7.8 percent on a year ago to 256.4 million euros ($380.4 million), taking the nine-month total to 777.5 million euros. At constant exchange rates, sales increased 6.1 percent in the nine months.

Ipsen still expects drug sales excluding the impact of exchange rates to grow between 7 and 9 percent. Total drug sales at constant rates grew 9.4 percent in the quarter and 7.1 percent in the nine months.

Next to a treatment for cervical dystonia, Ipsen's Dysport won regulatory clearance in the United States in April as a cosmetic anti-wrinkle treatment -- the only rival to Botox which is made by U.S. drugmaker Allergan (AGN.N). Botox sales were $1.3 billion in 2008.

As a cosmetic Dysport is marketed in the United States by Ipsen's partner Medicis Pharmaceutical (MRX.N). Ipsen has kept its U.S. rights for cervical dystonia.

Ipsen has made its expansion in the United States among its priorities. ($1=.6740 euros) (Reporting by Caroline Jacobs)