Naltrexone Prodrugs for Transdermal Delivery (Administrative Supplement)

Naltrexone, an opioid antagonist, is currently used in oral tablet form to help maintain opioid addicts in a drug-free state. Most recently, naltrexone has been indicated as an adjunct in the treatment of alcohol dependence, as well as reported to reduce alcohol craving in certain alcoholic populations. Transdermal delivery of naltrexone is desirable for opioid addicts and alcoholics in order to help reduce side effects associated with oral therapy and improve compliance. Naltrexone itself does not have the essential physicochemical properties that would allow a therapeutic dose of the drug to cross the human skin barrier. We plan to continue designing and synthesizing derivatives (prodrugs), which are more skin permeable than naltrexone, in order to make a therapeutically successful drug delivery system. We hypothesize that prodrugs of naltrexone will improve the transdermal delivery rate of naltrexone, and that these prodrugs will make excellent research tools for investigating quantitative structure-permeability relationships (QSPRs) for transdermal flux and concurrent metabolism. These prodrugs should improve naltrexone delivery rates across the skin, because they are more lipophilic, less crystalline, and therefore more soluble than naltrexone. The specific aims of this project include: (1) to synthesize a series of naltrexone prodrugs designed to elucidate fundamental QSPRs for transdermal flux and concurrent metabolism of the prodrugs, (2) to characterize the physicochemical parameters of the naltrexone prodrugs, including molecular weight, molecular volume, lipophilicity, hydrogen-bonding potentials, melting points, heats of fusion, and solubilities in select solvents, (3) to measure the naltrexone prodrugs' penetration and concurrent metabolism through human skin in vitro, (4) to characterize the pharmacokinetics of the naltrexone prodrugs in guinea pigs in vivo, and (5) to characterize the pharmacokinetics of the most promising naltrexone prodrugs in pigs in vivo. Correlation of our in vitro data with the in vivo models will aid in the creation of a reliable QSPR database, as well as help to identify the most promising prodrug for eventual human use.