FIG. 1.

Matrix of drug concentrations used during two-drug antiviral combination experiments. During each two-drug combination assay, individual drugs (A and B) were tested alone at five concentrations that spanned the linear region of their experimentally determined dose responses (data not shown). For drugs A and B, dose 1 was 0.16 times the IC₅₀, dose 2 was 0.33 times the IC₅₀, dose 3 equaled the IC₅₀, dose 4 was 3 times the IC₅₀, and dose 5 was 6 times the IC₅₀ (dose numbers are indicated by subscripts). To test the combination activity of drugs A and B, 11 combination doses were administered to cells, as indicated by the matrix.