Binding, drug-receptor distribution affected

The ready equilibration between free amine and ammonium salt is important for the formulation and activity of amine-based pharmaceuticals. The neutral forms are typically insoluble in water, and therefore the medications are sold in their salt forms, to allow for ready oral or intravenous administration. The pK of the amino function also affects the distribution, metabolism, exaction, and binding to receptor sites. Thus, after ingestion, the acidic environment of the stomach (pH 2-4) will keep the drug protonated, therefore minimizing absorption through the nonpolar gastric walls. Once in the intestines (pH 5-7), the acid-base equilibrium... 

---