* FDA panel due to discuss ocriplasmin recommendation on Thursday
* ThromboGenics remains confident
* Shares reach five-week low (Adds analyst, company comments, share price)
BRUSSELS, July 24 (Reuters) - ThromboGenics' main drug, the eye treatment ocriplasmin, may have a high rate of adverse side effects, the U.S. Food and Drug Administration said in a preliminary report made available on Tuesday.
The report was issued two days before a panel is due to discuss whether or not to recommend the drug for approval and sent ThromboGenics shares down as much as 19 percent to a five-week low.
"There are several adverse events which occur at a much higher rate in ocriplasmin treated patients which raise concerns about the drug's potential effect on the retina," the FDA said.
The FDA report added that the side effects may be transient and cause no long-term harm, but it did not have enough data to know for sure.
At 1410 GMT, ThromboGenics shares were down 7.6 percent at 23.13 euros.
However, KBC Securities analyst Jan De Kerpel said he was not so concerned, adding that the FDA often used harsh language.
"Before drawing the conclusion that we have now here very negative information in front of us, I need to see more data or clarification," he said.
ThromboGenics itself said it believed it can demonstrate to the FDA that the side effects are transient and remained confident the drug will be approved.
"We have evidence that these things are all transient. There is nothing that is really sustained. Of course, we will address this during the discussion," said Chief Financial Officer Chris Buyse.
"We are well prepared and we are very confident that this drug will be approved, hopefully after positive advice on Thursday."
ThromboGenics licensed the eye drug ocriplasmin in March to Novartis's opthalmic division to sell outside the United States, but it plans to market the product itself within the United States. (Reporting by Ben Deighton; editing by Philip Blenkinsop)