PK and PD Study of NPI-001 and Cysteamine Bitartrate

Inclusion Criteria: 1. Males or females, any race, ≥ 10 years of age. 2. Diagnosis of nephropathic cystinosis and able to cease cysteamine therapy for 2 days. 3. Females will be nonpregnant and nonlactating, and females of childbearing potential and males will agree to use contraception as detailed in the protocol. 4. Able to comprehend and willing to sign an informed consent /assent form and to abide by the study restrictions (travel as necessary, clinical phase 1 unit or similar for up to 3 days). Exclusion Criteria: 1. Have undergone kidney transplantation. 2. Are receiving dialysis treatment. 3. History of significant hypersensitivity to NAC or any ingredient of NPI-001 oral solution. 4. Participation in a clinical study involving administration of an investigational drug (new chemical entity) in the 30 days prior to Day 1. 5. Inability to provide blood samples, including difficulty with venous access. 6. Subjects who, in the opinion of the Investigator and/or Sponsor (or designee), should not participate in this study.