Absorption rate constant

The absorption rate constant K_a is a value used in pharmacokinetics to describe the rate at which a drug enters into the system. It is expressed in units of time⁻¹.^[1] The K_a is related to the absorption half-life (t_1/2a) per the following equation: K_a = ln(2) / t_1/2a.^[1]

K_a values can typically only be found in research articles.^[2] This is in contrast to parameters like bioavailability and elimination half-life, which can often be found in drug and pharmacology handbooks.^[2]