As an aside, you typically use a prodrug because you think it will lead to better drug properties than the parent compound.
This is really key. Sometimes you make a prodrug because the active drug isn't soluble enough or you can't crystalize it nicely or it unstable and degrades quickly.
The Claritin example is a good one. The prodrug requires metabolism into the active compound, but genetic variation can mean some people don't metabolize it well. There are also interactions with other drugs too. So they just changed to the active drug.
This is really key. Sometimes you make a prodrug because the active drug isn't soluble enough or you can't crystalize it nicely or it unstable and degrades quickly.
The Claritin example is a good one. The prodrug requires metabolism into the active compound, but genetic variation can mean some people don't metabolize it well. There are also interactions with other drugs too. So they just changed to the active drug.