ka - The "absorption rate constant" for a drug administered by a route other than the intravenous. The rate of absorption of a drug absorbed from its site of application according to first-order kinetics. ka is determined directly, or indirectly, as the slope of the linear relationship between the logarithm of the amount unabsorbed and t, when natural logarithms, i.e. logarithms to the base e, are used. The half-time for absorption is computed as 0.693/ka, i.e. ln 2/ka.
Cf. kel (kel), k0 (k0), t1/2 (t1/2), Half-Life, First-Order Kinetics, Cmax (Cmax)