If a drug is very hydrophilic, it will not get past the BBB and will instead show the following relative to lipophilic drugs:

If a drug is very hydrophilic, it will not get past the BBB and will instead show the following relative to lipophilic drugs:

• A. Higher Cv and Higher Kp
• B. Higher Cv and Lower Kp
• C. Lower Cv and Higher Kp
• D. Lower Cv and Lower Kp

Answer: (B)

When a drug is very hydrophilic, it faces the barrier of the blood-brain barrier (BBB), which is difficult to cross for non-lipid-soluble compounds. This means brain concentrations stay low relative to plasma, so the brain-to-plasma partition coefficient is small. In pharmacokinetic terms, the central (or central-compartment) distribution reflects how much drug remains in the blood and readily accessible fluids. Hydrophilic drugs tend not to move deeply into tissues, so a larger fraction stays in the central compartment, making the apparent central volume of distribution larger than for a lipophilic drug that distributes more widely into tissues (including brain). Therefore, a very hydrophilic drug shows a higher central volume and a lower brain-to-plasma ratio than a lipophilic drug.

When a drug is very hydrophilic, it faces the barrier of the blood-brain barrier (BBB), which is difficult to cross for non-lipid-soluble compounds. This means brain concentrations stay low relative to plasma, so the brain-to-plasma partition coefficient is small. In pharmacokinetic terms, the central (or central-compartment) distribution reflects how much drug remains in the blood and readily accessible fluids. Hydrophilic drugs tend not to move deeply into tissues, so a larger fraction stays in the central compartment, making the apparent central volume of distribution larger than for a lipophilic drug that distributes more widely into tissues (including brain). Therefore, a very hydrophilic drug shows a higher central volume and a lower brain-to-plasma ratio than a lipophilic drug.