What characteristics determine distribution into bone tissue?

• A. Bone has low perfusion and a dense matrix; distribution is slow and limited
• B. Bone is highly perfused and drug distributes quickly
• C. Bone distribution is identical to soft tissues
• D. Bone distribution is only determined by molecular weight

Answer: (A)

Bone distribution is controlled by how well blood reaches the tissue and by the mineralized, dense bone matrix itself. Bone has relatively low blood flow compared with highly perfused organs, and the mineralized matrix (hydroxyapatite with collagen) creates a barrier to rapid diffusion and provides binding sites for certain drugs. As a result, drugs take longer to reach bone and, once there, may accumulate or bind, leading to a distribution that is slow and limited overall. This contrasts with soft tissues that are highly perfused and allow faster distribution. Distribution is not determined solely by molecular weight; diffusion is also constrained by bone perfusion and binding to the bone mineral and matrix.