Poly(ethylene glycol) conjugated drugs and prodrugs: a comprehensive review.

Low molecular weight Poly(ethylene glycol) (PEG) (< 20,000)-drug conjugates, prepared over a 20-year period, have been scrutinized and their properties and efficacy reviewed. No commercial products have thus far been reported for these types of compounds. However, during the past 5 years a renaissance in the field of PEG-(anticancer) drug conjugates has taken place, initiated by the use of higher molecular weight PEGs (> 20,000), especially 40,000, which is estimated to have a plasma circulating half-life of approximately 8-9 h. This recent resuscitation of small organic molecule delivery by high molecular weight PEG conjugates was founded on meaningful in vivo testing using established tumor models and has led to a clinical candidate. Recent applications of high molecular weight PEG prodrug strategies to amino-containing drugs are also detailed.