Which characteristic promotes absorption of a drug across lipid membranes?

Which characteristic promotes absorption of a drug across lipid membranes?

• A. Lipid solubility
• B. Water solubility
• C. Large molecular weight
• D. Poor permeability

Answer: (A)

Membrane permeation across lipid barriers depends on a drug’s ability to partition into the lipid portion of the membrane. Lipid solubility (lipophilicity) allows the drug to dissolve in the hydrophobic core of the membrane and diffuse down its concentration gradient, which drives absorption through biological membranes like the gastrointestinal lining. Water-soluble drugs, by contrast, don’t readily enter the lipid core, so their passage by passive diffusion is limited, reducing absorption. Large molecular weight and poor permeability describe molecules that already have trouble crossing membranes, so they don’t promote absorption. Thus, the lipid-soluble nature of a drug best explains why it crosses lipid membranes efficiently.

Membrane permeation across lipid barriers depends on a drug’s ability to partition into the lipid portion of the membrane. Lipid solubility (lipophilicity) allows the drug to dissolve in the hydrophobic core of the membrane and diffuse down its concentration gradient, which drives absorption through biological membranes like the gastrointestinal lining. Water-soluble drugs, by contrast, don’t readily enter the lipid core, so their passage by passive diffusion is limited, reducing absorption. Large molecular weight and poor permeability describe molecules that already have trouble crossing membranes, so they don’t promote absorption. Thus, the lipid-soluble nature of a drug best explains why it crosses lipid membranes efficiently.