A Study of Whether 2 New Oral Formulations of a Strong Pain Killer Release the Same Amount of Drug Into the Body as the Marketed Medication

Inclusion Criteria * Healthy male or female subjects aged 18 to 55 inclusive. * Female subjects who are sexually active or become sexually active must be willing to use highly effective methods of contraception throughout the study. A highly effective method of birth control is defined as one which results in a low failure rate (i.e. less than 1% per year) when used consistently and correctly such as sterilisation, implants, injectables, combined oral contraceptives, some IUDs (Intrauterine Device), or vasectomised partner. * Female subjects less than one year post-menopausal must have a negative serum pregnancy test and be non-lactating. * Female subjects who have been post-menopausal for \> 1 year and have elevated serum follicle-stimulating hormone (FSH) or are treated with hormone replacement therapy (HRT). * Male subjects must be willing to use contraception with their partners throughout the study and for 30 days after completion of the study and agree to inform the Investigator if their partner becomes pregnant during this time. * Body weight ranging from 55 to 100 kg and a BMI ≥ 18.5 and ≤ 29.9. * Healthy and free of significant abnormal findings as determined by medical history, physical examination, vital signs, laboratory tests and ECG. * Willing to eat all the food supplied throughout the study. * The subject's primary care physician has confirmed within the last 12 months that there is nothing in their medical history that would preclude their enrolment into a clinical study. Exclusion Criteria * Any history of drug or alcohol abuse. * Any history of conditions that might interfere with drug absorption, distribution, metabolism or excretion. * Use of opioid or opioid antagonist-containing medication in the past 30 days. * Any history of frequent nausea or vomiting regardless of etiology. * Any history of seizures or symptomatic head trauma. * Paralytic ileus, respiratory depression, hypoxia or elevated carbon dioxide levels in the blood. * Participation in a clinical drug study during the 90 days preceding the initial dose in this study. * Subjects must not participate in both the pilot and definitive phase or in more than one Cohort. * Any significant illness during the 4 weeks preceding entry into this study. * Use of any medication including vitamins, herbal and/or mineral supplements during the 7 days preceding the initial dose or during the course of this study (with the exception of the continued use of HRT and contraceptives). Note: subjects taking oral contraceptives containing CYP3A4 inhibitors such as gestodene should be excluded as this may lead to elevated plasma concentrations.