Question

3 multiple choice 1 point
when comparing smds, those with a lower volume of distribution tend to be metabolized and excreted more rapidly than those with a higher volume of distribution. the smd methotrexate, which can be used to treat rheumatoid arthritis, has a $v_d$ of 28-56 l; the protein therapeutic tocilizumab, which can also be used to treat rheumatoid arthritis, has a $v_d$ of 6-8 l. would you expect the half-life of tocilizumab to be longer or shorter than that of methotrexate, and why?
the half-life of tocilizumab would be longer because the metabolism of protein therapeutics occurs primarily inside of cells and is not directly dependent on liver metabolism.
the half-life of tocilizumab would be shorter because protein therapeutics are inherently more unstable than smds and tocilizumab would therefore be metabolized faster.
the half-life of tocilizumab would be shorter because it remains in the systemic circulation and will therefore be metabolized and excreted faster.
the half-life of tocilizumab would be longer because it is a larger molecule and will therefore be metabolized more slowly.

Explanation:

Volume of distribution ($V_d$) reflects how widely a drug distributes outside the bloodstream. A lower $V_d$ (like tocilizumab's 6-8 L) means the drug stays mostly in systemic circulation, where it is more accessible to metabolic and excretory pathways, leading to faster clearance and a shorter half-life. The other options are incorrect: protein therapeutics do undergo liver-related processing, stability alone does not explain this relationship, and size does not override the impact of distribution on half-life here.

Answer:

C. The half-life of tocilizumab would be shorter because it remains in the systemic circulation and will therefore be metabolized and excreted faster.