Biotechnology stocks are among the most risky securities, fluctuatingwidely on the vagaries of investors, and Friday Gilead Sciences Inc.was reminded of the market's volatility.

The Foster City, Calif., company's lead product, Vistide (cidofovir),received a unanimous vote of confidence from FDA advisorycommittees on antiviral and ophthalmic drugs. The eight panelmembers recommended approval of Vistide for AIDS-relatedcytomegalovirus (CMV) retinitis, a potentially blinding disease thatinfects 90 percent of AIDS patients.

If cleared by the FDA, Vistide, a nucleotide analogue, would beGilead Science's first marketed product.

The recommendation, however, came as the stock market closedFriday, too late to offset reports earlier in the day the advisorycommittee members appeared concerned about preclinical toxicologydata showing Vistide was linked to tumors in certain female rats usedin animal studies of the drug.

Investors aware of the panel's early questions began abandoningGilead Science's stock (NASDAQ:GILD), sending it plummeting$8.25 to $26.50, a 24 percent drop, before NASDAQ halted tradingat about 11 a.m.

Later in the hearing, the committee members apparently weresatisfied the tumor side effects seen in rats were not an issue.

Lana Lauher, Gilead's spokeswoman, noted the advisory panel'sunanimous decision was based on Vistide's safety and efficacyprofile. The company submitted data from three Phase III studies, shesaid, and committee members were told no non-AIDS relatedmalignancies were reported in the more than 500 patients who havereceived the drug.

In a statement released after the meeting Friday, Gilead officials said,"Data from preclinical studies completed in 1994 in female Sprague-Dawley rats indicated cidofovir caused mammary tumors in thisanimal model. In a 52-week study in primates no carcinogenicity wasobserved."

Gilead officials have said the clinical trials revealed the dose-limitingside effect of Vistide is kidney toxicity, which can be managed.

Data from all three clinical trials of Vistide showed the drug achievedstatistical significance, when compared to placebo, in slowingprogression of the disease.

The third and most recent study, reported last week, was halted after64 of 90 patients were enrolled because the drug had demonstrated itseffectiveness. (See BioWorld Today, March 12, 1996, p. 1.)

Details of the third trial were released for the first time at theadvisory committee hearing. Gilead officials said the results showedVistide slowed mean progression time of the virus to 89 days inAIDS patients newly diagnosed with CMV retinitis. Progression ismeasured from the time the disease is detected. The mean time toprogression for patients not receiving the treatment was 21 days.

Unlike current treatments that are administered daily, Vistide is takenonce a week for the first two weeks and then once every other week.

Drugs approved for AIDS-related CMV retinitis are foscarnet, madeby Astra AB, of Sodertlje, Sweden, and ganciclovir, made by RocheHoldings Ltd., of Basel, Switzerland. Chiron Corp., of Emeryville,Calif., received approval March 5, 1996, for Vitrasert, which is anintraocular implant of ganciclovir.

Among those supporting approval of Vistide Friday were members ofvarious AIDS activist groups, including the Houston Center forAIDS, Act Up New York, and the Miami-based Florida AIDS ActionCouncil. n

-- Charles Craig

(c) 1997 American Health Consultants. All rights reserved.