pH partition theory

Abstract

The pH partition theory (or pH partition hypothesis, also referred to sometimes as the theory of nonionic diffusion) was conceived during the first half of the twentieth century upon prior observations which suggested that only lipophilic chemical species could cross lipoid biological barriers. The theory states that since most drugs are weak electrolytes, only the nonionized species will be able to permeate across biological barriers; subsequently, weak bases would preferably distribute to acidic body compartments, whereas weak acids would preferably remain in basic ones. The tendency of an ionizable molecule to accumulate in those cells or organelles where the ionized species predominates is known as ion trapping.