CHICAGO, May 19 (Reuters) - An injectable gel used to improve the appearance of lips, cheeks and other facial features may cause swelling, nodules and other problems, researchers in Spain reported on Monday.

The compound, called polyalkylimide, has been used primarily in Europe, said Dr. Jaume Alijotas-Reig, and colleagues at Vall d'Hebron University Hospital and Autonomous University in Barcelona, Spain.

Early reports on polyalkylimide injections indicated there were no significant signs of rejection of the material or adverse reaction to introduction of a foreign substance, the researchers said.

"However, more recent evidence refutes these statements, and so the complete safety of polyalkylimide implant gels can no longer be assured," they added in a small study published in the Archives of Dermatology.

Their findings were based on 25 patients, eight of whom had a previous implant of one kind or another, including silicone breast implants.

The group developed a variety of problems including swelling, hardening and swollen or tender nodules near the injection site, as well as fever, arthritis and dry eyes or mouth a year or more after the treatment.

After nearly two years, 11 of the group appeared to be free of adverse effects but 10 still had recurrent problems, the study found.

"We do not know the real number of cases that have developed delayed adverse effects because of the tendency of many physicians to not report negative events," the researchers said in their report.

The compound, which came on the market in 2001, "is increasingly one of the most commonly used fillers in Europe," they said.

Considering the increased use of the implants, doctors "should be aware that intermediate or delayed adverse effects can occur ... just as they can with collagen, polyacrylamide, polylactic acid or methacrylate," the researchers said, referring to other compounds used as cosmetic fillers.

The compound, sold as Bio-Alcamid, is patented by Polymekon Sri of Brindisi, Italy, and marketed in partnership with Ascente Medical Corp of Toronto, both privately held.

Polymekon's website says studies have proven it safe and effective. (Reporting by Michael Conlon; editing by Mohammad Zargham)

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