TABLE 1.

Measurement of intracellular drug interactions between AZT and d4T

Drug treatmenta	% GFP-positive target cellsb	Mean % GFP-positive target cells	Drug resistance indexc	P value for antagonismd
No drug	18.62	20.09
	24.16
	20.08
	17.49
10 μM AZT	7.61	7.15	0.356
	6.70
	7.59
	6.71
10 μM d4T	6.83	6.54	0.325
	7.04
	5.74
10 μM AZT plus 10 μM d4T	7.14	7.25	0.361	<0.001
	8.76
	5.78
	7.33

^aJurkat cells were infected in replicate with pseudotyped reporter viruses carrying the NL4-3 gag-pol sequence in the presence of the indicated drug(s). The drug(s) was added to target cells 16 h before infection and was maintained throughout the experiment.

^bMeasured 48 h after infection.

^cThe drug resistance index is the ratio of the measured replication in the presence of drug(s) to that in the absence of drugs.

^dAntagonism is scored according to the fraction product principle. f₀ represents the fraction of infected cells in the absence of drug; f_AZT and f_d4T represent the fractions of infected cells in the presence of 10 μM AZT and 10 μM d4T, respectively; f_(AZT+d4T) represents the fraction of infected cells in the presence of the combination of 10 μM AZT and 10 μM d4T. If AZT and d4T function independently, then f_(AZT+d4T)/f₀ should equal f_AZT/f₀ × f_d4T/f₀; if f_(AZT+d4T)/f₀ > f_AZT/f₀ × f_d4T/f₀, then there is antagonism, and if f_(AZT+d4T)/f₀ < f_AZT/f₀ × f_d4T/f₀, then there is synergism. f₀, f_AZT, f_d4T, and f_(AZT+d4T) were measured as the means of three or four replicates for each condition. The P value is of the coefficient for the interaction term ln (f_AZT/f₀) × ln (f_d4T/f₀) being equal to zero in a multilinear regression.