<P> A drug in blood exists in two forms: bound and unbound . Depending on a specific drug's affinity for plasma protein, a proportion of the drug may become bound to plasma proteins, with the remainder being unbound . If the protein binding is reversible, then a chemical equilibrium will exist between the bound and unbound states, such that: </P> <Dl> <Dd> <Dl> <Dd> Protein + drug ⇌ Protein - drug complex </Dd> </Dl> </Dd> </Dl> <Dd> <Dl> <Dd> Protein + drug ⇌ Protein - drug complex </Dd> </Dl> </Dd> <Dl> <Dd> Protein + drug ⇌ Protein - drug complex </Dd> </Dl>

If a patient takes a drug that is highly protein-bound would there be a drug reaction