However, smaller lipid materials or lipid soluble materials, such as diethyl ether, halothane, can easily enter the brain. These compounds are used as general anesthetics. In the kidney there are a number of regions important for drug elimination. In the tubules drugs may be reabsorbed. Blood capillaries and renal glomerular membranes.
Active transport requires a carrier molecule and a form of energy.
Passive Diagram XI-5, Diagram of Passive Transport with a Concentration Gradient Most drugs cross biologic membranes by passive diffusion. Diffusion occurs when the drug concentration on one side of the membrane is higher than that on the other side. Drug diffuses across the membrane in an attempt to equalize the drug concentration on both sides of the membrane. If the drug partitions into the lipid membrane a concentration gradient can be established. This parameter is related to the size and lipid solubility of the drug and the viscosity of the diffusion medium, the membrane.