What role does ionization play in drug absorption?

Ionization significantly impacts the absorption of drugs, primarily due to the nature of cell membranes. Cell membranes consist of lipid bilayers, which present a barrier to charged (ionized) substances. The principle of ionization is crucial in pharmacokinetics because it determines a drug's ability to cross these membranes.

When a drug is ionized, it carries a charge that limits its ability to diffuse through lipid membranes. Non-ionized (or neutral) drugs, on the other hand, can more easily penetrate these membranes due to their lipophilic nature. As a result, non-ionized forms of drugs tend to be absorbed more readily into the bloodstream after oral administration or other routes.

The statement indicating that ionized drugs are repelled by cell membranes highlights this important distinction; it shows that the charge on an ionized drug prevents it from moving through the lipid-rich environment of cell membranes, leading to limited absorption. Thus, understanding the characteristics of ionization helps in predicting the absorption and overall bioavailability of drugs in the body.