The Study of GW493838, an Adenosine A1 Agonist, in Peripheral Neuropathic Pain

Inclusion criteria (subjects must meet all of the following criteria in order to be eligible for this study): * Females of non-child-bearing potential * diagnosis of peripheral neuropathic pain as a result of: postherpetic neuralgia (PHN) from shingles for at least 3 months duration OR focal neuropathic pain related to nerve injury caused by trauma or surgery * defined area of pain Exclusion criteria * discontinue agents for the treatment of neuropathic pain * unable to refrain from alcohol and sedative use during the study * confounding chronic pain which could not be differentiated from the peripheral neuropathic pain under study * intractable pain of unknown origin or active infection in the area of nerve injury. * clinically significant medical history or abnormality found on physical examination, laboratory assessment or ECG at Screening or Baseline * severe asthma that has required oral corticosteroid use in the last 12 months or the subject had severe asthma that required, at anytime, hospitalization or mechanical ventilation support. * clinical evidence of major depression (by medical history) except those subjects controlled by SSRIs. * a known allergy or hypersensitivity to any of the investigational products (including rescue analgesia- acetaminophen), or pharmacological class of the investigational product (i.e. adenosine) and/or investigational product excipients. * a clinically significant abuse of substances, defined as: Patterns of substance intake consistent with disruption of normal function in society; Past or current impairment of organ function reasonably related to substance intake; Any indication of difficulty in abstaining from substances for the duration of the study. * had previously participated in a clinical study during the past 30 days in which the subject was exposed to an investigational or non-investigational drug or device * currently participating in another clinical study in which the subject was exposed to an investigational or non-investigational drug or device * prior blood reduction (450 mL or more) during the previous 30 days * at risk of non-compliance * a woman of childbearing potential or a woman who was lactating.