Which property of lipid-soluble drugs assists in permeating cell membranes?

Lipid-soluble drugs primarily permeate cell membranes through their ability to dissolve in the lipid bilayer that forms the cellular membrane. This property of solubility allows these drugs to readily diffuse across the membrane, which is composed of phospholipids that have hydrophobic (water-repellent) tails.

When a drug is lipid-soluble, it can easily integrate into the membrane and move across it without requiring transport mechanisms. This is crucial because many cells surround themselves with lipid membranes to maintain an internal environment distinct from the outside, and lipid solubility is key for a drug's absorption, distribution, and eventual therapeutic action within the body.

Other factors like size, charge, and stability can influence drug behavior, but they do not directly relate to the ability to traverse the lipid layers of the membrane in the same fundamental way that solubility does. Size may affect how easily a drug can fit through membrane pores, but lipid solubility is the primary determinant for passive diffusion across membranes. Charge can influence a drug's ability to enter cells, as charged molecules may have difficulty passing through the nonpolar lipid layers. Stability is essential for a drug's shelf-life and effectiveness but does not directly impact membrane permeability.