Study in Healthy Volunteers to Investigate the Effects of Rifampin on the Pharmacokinetics of NKTR-118

Inclusion Criteria: * Provision of signed and dated, written informed consent prior to any study-specific procedures. * Male and female (nonchildbearing potential, nonlactating) healthy volunteers aged 18 to 55 years inclusive, with suitable veins for cannulation or repeated venipuncture. * Female volunteers must have a negative pregnancy test at screening and at admission, must not be lactating, and must be of nonchildbearing potential. * Male volunteers should be willing to use barrier contraception ie, condoms, from the first day of dosing until 3 months after dosing with the IP. The female partner should use contraception during this period. * Volunteers must have a BMI between 18 and 30 kg/m2, inclusive, and weigh at least 50 kg. Exclusion Criteria: * Any clinically significant disease or disorder (eg, cardiovascular, pulmonary, gastrointestinal, liver, renal, neurological, musculoskeletal, endocrine, metabolic, malignant, psychiatric, or major physical impairment), as judged by the Investigator. * Any clinically significant illness, medical/surgical procedure or trauma, in the opinion of the Investigator, within 4 weeks of the first administration of IP. * Any clinically significant abnormalities in clinical chemistry, hematology, or urinalysis results as judged by the Investigator. * Significant orthostatic reaction at enrollment as judged by the Investigator. * Abnormal vital signs, after 10 minutes supine rest as defined in protocol.