Ketamine in Chronic Kid's (KiCK) Pain

Inclusion Criteria:

* Subject, parent, or guardian willing and able to give informed consent
* NRS for pain over the past 24 hours \>4 at baseline
* Chronic pain, which has been present for \>3 months, or persisting longer than is normal for the underlying diagnosis
* Chronic pain related to physiologic diagnoses including but not limited to: cancer, rheumatologic disease, sickle cell anemia, cystic fibrosis, pancreatitis, and neuromuscular disease (e.g. Duchenne muscular dystrophy)
* Able to tolerate and cooperate with neurocognitive assessment
* Age 8-20 years old

Exclusion Criteria:

* If they are known or suspected to have drug addiction
* Uncontrolled psychiatric disorder such as depression, schizophrenia, or bipolar disorder
* Uncontrolled hypertension
* Known liver disease or elevation of AST or ALT greater than 3 times the upper limit of normal.
* Previous intolerance or allergic reaction to ketamine
* Pregnancy
* Use of CYP3A4 inhibitors or inducers within the 2-week period prior the study drug administration or within 5 half-lives of the respective medication, whichever is longer, until study conclusion.
* Consumption of grapefruit or grapefruit products from at least 2 weeks prior to study drug administration until study conclusion.