 The main purpose of this study is to determine if it is safe to use the study drug, clavulanic acid, in combination with cocaine. In this study, subjects will receive intravenous i.v. cocaine and the study drug, clavulanic acid. The safety of clavulanic acid is being studied so future studies can be done to find out if this drug is helpful in treating cocaine dependence. Currently, there is no available medication treatment for cocaine dependence. 