LONDON - Shares in Scotia Pharmaceuticals plc fell 63 percent Tuesday to close at 45.5 pence after the company said it has received notification from the FDA that its application for Foscan, a photodynamic therapy for head and neck cancer, is not approvable.

The company is not sure what the problem is, and said it could take weeks before it knows what is needed to put it right. "This is an area of unchartered water - we are talking about a new type of treatment in an area of unmet therapeutic need," CEO Rob Dow told BioWorld International.

The FDA helped Scotia to design the pivotal trial, initially involving 50 people, and then expanded to 64. "Although it agreed to the design of the trial with us, I think when they looked at the data, the efficacy demonstrated in the number of patients so far was not enough for approval," Dow said.

"The data show clinical benefit. I think the point may be, 'Have we shown it in enough people?'"

Dow said he will not be sure what further data is required until he has a face-to-face meeting with the FDA. "If the FDA wants data on a bigger number of patients, we have data on 147 people we could submit straightaway. But it could be that the FDA wants another study, which will take significantly longer."

Scotia, based in Stirling, Scotland, has enough money to last until March 2001.

Dow said, "Working with the FDA to resolve this is an interactive process. We have got enough time to find out what needs to be done, and tell our shareholders and bondholders and ask for their support.

"For a small company in the financial position we're in, this is a serious setback. In the industry overall, many people go through non-approvable letters and go on to get approvals."

Scotia is in discussions to find a marketing partner for Foscan and Dow said these remain live despite the setback. The submission of Foscan in Europe is ongoing.