TABLE 1.

Effect of exogeneously added guanosine on the anti-YFV 17D and anti-hPIV3 activity of ribavirin, EICAR, and MPA in Vero cells^a

Amt (μg/ml) of guanosine added	EC50 for antiviral activity
	YFV 17Db			hPIV3c
	Ribavirin	EICAR	MPA	Ribavirin	EICAR	MPA
0 (control)	40 ± 9.0	1.05 ± 0.07	0.06 ± 0.03	27 ± 4.6	1.90 ± 0.22	0.055 ± 0.005
25	>100	≥21	>2.5d	>100	>100	>100
10	>100	10 ± 5.6	0.15 ± 0.06	>100	>100	2.5
2.5	>100	1.5 ± 0.1	0.06 ± 0.06	60	3.97	0.25
1.0	≥86	1.2 ± 0.1	0.057 ± 0.008	50	1.99	0.059

^aGuanosine at the concentrations used had no effect on virus-induced CPE formation.

^bData against YFV 17D are from two independent experiments (and up to eight separate determinations).

^cData against hPIV3 are from one or two independent experiments (and up to three separate determinations in the latter case).

^dThe highest concentration used in one experiment was 2.5 μg/ml. In another experiment, the EC₅₀ was >100 μg/ml.