In a Phase II study (M97-720) through 204 weeks of treatment, genotypic analysis of viral isolates was successfully conducted in 11 of 16 patients with confirmed HIV RNA above 400 copies/ ml revealed no primary or active site mutations in protease (amino acids at positions 8, 30, 32, 46, 47, 48, 50, 82, 84 and 90) or protease inhibitor phenotypic resistance.