What is the volume of distribution and how does it affect loading dose calculations?

• A. Volume of distribution is the actual physical space in the body where drug resides; smaller Vd means a larger loading dose.
• B. Volume of distribution is the rate of drug elimination; higher Vd means a smaller loading dose.
• C. Volume of distribution measures the time to peak concentration; Vd does not affect loading dose.
• D. Volume of distribution is a theoretical space in which the drug distributes; a large Vd means a larger loading dose is needed to achieve target plasma concentration.

Answer: (D)