What characteristics does weak electrolytes give drugs?

What characteristics does weak electrolytes give drugs?

• A. Hydrophilic and lipophilic
• B. Hydrophobic only
• C. Lipophilic only
• D. Neither

Answer: (A)

Weak electrolytes are partly ionized in solution, so a drug exists as both an ionized (hydrophilic) form and a nonionized (lipophilic) form. This dual character lets the drug dissolve in water due to the ionized portion while the nonionized portion can partition into lipid membranes to cross barriers. The balance between these forms depends on pH and the drug’s pKa, so near the pKa you have meaningful amounts of both forms, giving the molecule both hydrophilic and lipophilic properties. That combination is why the correct answer is hydrophilic and lipophilic. If a drug were only hydrophobic, solubility in aqueous fluids would be poor; if it were only lipophilic, aqueous solubility would also be poor.

Weak electrolytes are partly ionized in solution, so a drug exists as both an ionized (hydrophilic) form and a nonionized (lipophilic) form. This dual character lets the drug dissolve in water due to the ionized portion while the nonionized portion can partition into lipid membranes to cross barriers. The balance between these forms depends on pH and the drug’s pKa, so near the pKa you have meaningful amounts of both forms, giving the molecule both hydrophilic and lipophilic properties. That combination is why the correct answer is hydrophilic and lipophilic. If a drug were only hydrophobic, solubility in aqueous fluids would be poor; if it were only lipophilic, aqueous solubility would also be poor.