TABLE 1.

GS 4071 inhibits the replication and neuraminidase activity of influenza A and B viruses in vitro

Virus	IC50a (nM) of GS 4071		IC50 (nM) of zanamivir
	Culture assayb	Enzymatic assayc	Culture assay	Enzymatic assay
Laboratory strains
A/WS/33 (H1N1)	22	1.0	19	0.7
A/FM/1/47 (H1N1)	24	NDd	20	ND
A/Victoria/3/75 (H3N2)	0.6	0.5	3.5	1.7
A/Port Chalmers/1/73 (H3N2)	0.8	0.3	3.1	1.1
B/Mass/3/66	117	0.8	90	1.7
B/Hong Kong/5/72	155	1.7	150	1.0
Clinical isolates
A/Texas/36/91 (H1N1)	94	0.5	70	0.3
A/Johannesburg/33/94 (H3N2)	40	0.8	241	4.6
B/Harbin/07/94	91	2.0	30	2.1

^aIC₅₀s are taken to be the concentration of compound necessary to reduce the plaque number or the extent of cell killing by 50% in tissue culture assays or the enzymatic activity by 50%, relative to duplicate samples assayed in the absence of inhibitor. 

^bReplication in tissue culture was determined by a plaque reduction assay for the laboratory strains and by a CPE assay for the clinical isolates. Values represent the means obtained from at least three independent experiments except in the case of A/Johannesburg/33/94 (H3N2) which was tested only twice. 

^cEnzymatic assays were performed as described in the text with tissue culture medium harvested from cultures in which full cell death occurred. Values represent the means of two independent experiments. 

^dND, not determined.