Structure Modification of Drugs or Prodrugs Influencing Their Bioavailability and Therapeutic Effect

Prodrugs are inactive derivatives of active drug substances which, on undergoing an enzymatic or chemical transformation in vivo, release the active parent drug that can then elicit the desired pharmacodynamic effect. Prodrugs can be classified into carrier prodrugs and bioprecursors. In most cases, carrier prodrugs are simple chemical derivatives of compounds that are only one or two chemical or enzymatic steps away from the active parent drug. Bioprecursors require enzymes of biotransformation phases for their activation; the active species results from a cascade of metabolic reactions involving oxidative/reductive processes. Currently codrugs (mutual prodrugs) become an efficient approach to drug optimization. The soft drug approach is briefly mentioned to clarify the difference between soft drugs and prodrugs.