3. Precursors and metabolites

A precursor (M-P) is a compound prepared from an active drug (M) to which a product (P) is attached, in order to modify its physico-chemical characteristics (stability, solubility, lipophilicity...) and improve its pharmacokinetic properties. After administration, bioconversion of the precursor leads to regeneration of the initial constituents, following chemical or enzymatic transformation [12] (figure 11 ).

Precursors are different from the metabolites formed from a drug, which may or may not have the same pharmacological properties as the drug itself.