Volume of Distribution and Plasma Protein Binding?

[Bathrover]

I am a little confused about how volume of distribution is defined,

Vd = Dose / [Drug]plasma

For drugs that are bound to plasma proteins, do they still count toward the plasma or is the denominator considering only the free drug and thus if a drug binds plasma proteins more rigorously it will in effect reduce the [Drug]plasma and increase Vd?

Thanks =)

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[seminoma]

Drugs that bind very strongly to plasma proteins are trapped in the plasma and thus have a very low Vd.