To assess whether an opioid antagonist has any impact on the release of a strong painkiller in the blood when it is given to healthy volunteers when they have eaten and also when they have fasted.

This is an exploratory study to assess the influence of an opioid antagonist on the pharmacokinetics of a strong painkiller when co-administered in a fasted and fed state.

Determination is by measurement of drug concentrations in the blood at serial collection time points pre-dose until 32 hours post-dose, following an administration of a single oral dose. Pharmacokinetics parameters of AUC and Cmax are the primary endpoints.

Healthy male or female subjects aged 18 to 55 inclusive Healthy and free of significant abnormal findings as determined by medical history, physical examination, vital signs, laboratory tests and ECG.