The same day the FDA approved Hoffman-La RocheInc.'s Invirase for marketing, a study showed that anotherprotease inhibitor, ritonavir, developed by AbbottLaboratories appeared to confirm that the new class ofanti-HIV compounds is more effective in fighting thevirus than the currently available nucleoside analogdrugs.

Results from the monotherapy studies of ritonavir werereported in Thursday's issue of the New England Journalof Medicine. The trials involved 84 patients in Spain,Australia and The Netherlands who received one of fourescalating doses of the protease inhibitor or a placeboover four weeks. Following the initial month oftreatment, all patients continued receiving ritonavir.

Standard markers for measuring effectiveness of AIDSdrugs are an increase in CD4 counts and a decrease ofviral load. Researchers said the studies showed ritonaviralone out-performed the currently available nucleosideanalogs, such as AZT.

In addition, the researchers found that after 32 weeks,patients receiving the highest dose, 600 mg, sustainedtheir reduction in viral load and their increase in CD4counts. The gain in T cell counts also was the largest atthe highest dose.

Douglas Petkus, a spokesman for Abbott Laboratories, ofAbbott Park, Ill., said the pharmaceutical companyexpects to file a new drug application (NDA) for ritonavirwith the FDA by the end of the first quarter of 1996.

Merck & Co., of Whitehouse Station, N.J., also isdeveloping an HIV protease inhibitor and expects to fileits NDA early next year.

Hoffman-La Roche, of Nutley, N.J., a subsidiary of Basel,Switzerland-based Roche Holdings Ltd., was first to filean NDA for a protease inhibitor and received FDAapproval of Invirase (saquinavir mesylate) Thursday in 97days, a record for an AIDS drug review. (See BioWorldToday's Special News Bulletin, Dec. 7, 1995.)

Wall Street analysts have said ritonavir and Merck'sprotease inhibitor are more potent than Invirase. But theAbbott and Merck products also apparently have greateradverse side effects than Roche's drug.

Protease inhibitors, which attack HIV replication at theend of the cycle, are considered safer and more effectivethan the nucleoside analogs, which strike the virus earlierin the replication process. Invirase was approved for usein combination with nucleoside analogs. n

-- Charles Craig

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