(2) Das(i)=Dma (fa(i)/(1-fa(i)))1/ma


Table 5. CI calculation between two drugs a and b at the 50% effect level under three alternative conditions: additive, synergic, antagonistic. To obtain CI as a function of the effect level i, the calculation has to be repeated for each arbitrary level i between 0 and 1. A 95% confidence interval around D in general and around Dm in particular, can be computed using the formulas for standard error (SE, eq. 13 and eq. 14). A 95% confidence interval around CI at any effect level i can be computed from the standard error formulas presented in eq. 12, 13 and 14

Combined drugs a+b

Dm (uM) #(1) 10 30 17 14 24.4 m #(1) 33 3 3 3

Dac(i) #(4) 4.25 3.5 6.1 Dbc(i) #(5) 12.75 10.5 18.3 p/(p+q) #(6) 0.25 0.25 0.25 q/(p+q) #(6) 0.75 0.75 0.75 CI (i) #(7) 1.03 0.82 1.59

SE(D) = 1/2 . {10 [log(D)+SE(log(D)]-10 [log(D)-SE(log(D)]} **(eq. 13)**

A 95% confidence interval around D in general and around Dm in particular, can be

A 95% confidence interval around CI at any effect level i can be computed from the

}

1/2 **(eq. 12)**

SE(CI(i))={{ Dac(i)/ Das(i) . [SE(Dac(i)/ Dac(i)+ SE(Das(i)/ Das(i)]}2

Single drug a

fa(i) 0.5 Das(i) #(2) 10
