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Alpha (α) rate constant
The first-order rate constant for the exponentialdistribution of drug from the plasma into the tissues. It can be found from the slope of the distribution portion of a two-compartment curve, or a hockey-stick curve, and the half-life for distribution for a two-compartment drug can be calculated from 0.693/α. It is a proportionality constant (similar to kel and β) with units of “per time” and indicates the proportion of remaining drug that will be distributed in unit time if the current rate of distribution is maintained. The span of the exponential curve describing first-order distribution lies between the A+B intercept and the B-intercept. A value for α from a two-compartment plasma concentration versus time curve can be obtained by manual curve-stripping, or through use of software.