In this four-period crossover study , healthy subjects aged 18-45 years were randomized to receive a single intact , oral 45-mg tablet of one of three hydrocodone ER prototypes ( low - , intermediate - , or high-level coating ) or an intact , oral tablet of hydrocodone IR/acetaminophen ( APAP ) 10/325 mg every 6 h until four tablets were administered , with each of the four treatments administered once over the four study periods .