Which statement about tissue compartments and equilibration with blood is true?

Which statement about tissue compartments and equilibration with blood is true?

• A. All equal and equilibrate instantly
• B. Some compartments equilibrate instantly; others have slower distribution
• C. No compartments equilibrate with blood
• D. All compartments distribute at identical rates

Answer: (B)

Distribution of a drug into body tissues is not uniform; the body is modeled as compartments with different perfusion and tissue binding characteristics. The central compartment, which includes blood and well-perfused organs, is typically in rapid or near-instant equilibrium with the blood, while peripheral compartments (like fat or less-perfused tissues) gain the drug more slowly due to slower blood flow and barriers to transfer. So, some compartments reach equilibrium with the blood quickly, while others take longer to equilibrate. This difference in transfer rates explains the two-phase pattern often seen in plasma concentration over time: an initial rapid distribution phase followed by a slower distribution phase driven by the slower compartments.

Distribution of a drug into body tissues is not uniform; the body is modeled as compartments with different perfusion and tissue binding characteristics. The central compartment, which includes blood and well-perfused organs, is typically in rapid or near-instant equilibrium with the blood, while peripheral compartments (like fat or less-perfused tissues) gain the drug more slowly due to slower blood flow and barriers to transfer. So, some compartments reach equilibrium with the blood quickly, while others take longer to equilibrate. This difference in transfer rates explains the two-phase pattern often seen in plasma concentration over time: an initial rapid distribution phase followed by a slower distribution phase driven by the slower compartments.