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.{{cite book|author=John E. Murphy|title=Clinical Pharmacokinetics|url=https://books.google.com/books?id=0P07DwAAQBAJ&pg=PT26|date=1 July 2016|publisher=ASHP|isbn=978-1-58528-538-9|pages=26–}} The K_a is related to the absorption half-life (t_1/2a) per the following equation: K_a = ln(2) / t_1/2a.

K_a values can typically only be found in research articles.{{cite book|author1=Miles Hacker|author2=William S. Messer|author3=Kenneth A. Bachmann|title=Pharmacology: Principles and Practice|url=https://books.google.com/books?id=5YDMmjWXe-AC&pg=PA257|date=19 June 2009|publisher=Academic Press|isbn=978-0-08-091922-5|pages=257–}} This is in contrast to parameters like bioavailability and elimination half-life, which can often be found in drug and pharmacology handbooks.