Inclusion Criteria:
* Male and female subjects
* Aged 18 to 55 years
* For female subjects, surgically sterile or at least 2 years menopausal, or using an acceptable method of birth control. If of childbearing potential, have a documented negative blood or urine pregnancy test within 24 hours prior to dosing.
* Clinical laboratory values \<2 times upper limit of normal (ULN) or deemed not clinically significant by the investigator
* Ability to understand the requirements of the study, provide written informed consent, abide by the study restrictions, and agree to return for the required assessments
Exclusion Criteria:
* Human immunodeficiency virus (HIV) infection, or hepatitis or other ongoing infectious disease.
* Current evidence of alcohol abuse (greater than 4 units of alcohol on most days; 1 unit = 1/2 pint of beer, 1 glass of wine or 1 oz. of spirits), or in the option of the investigator that subject may be alcoholic.
* Current abuse of illicit substances, using the Diagnostic and Statistical Manual (DSM) IV definition of drug abuse.
* Current smoker or use of other tobacco products.
* Currently pregnant, planning to become pregnant during the course of the study, or nursing mother.
* Type I or Type II diabetes.
* Malignancy in the last 5 years, with the exception of nonmetastatic basal cell or squamous cell carcinoma of the skin or localized carcinoma in situ of the cervix.
* Currently taking prescription or over-the-counter medications including herbal therapies, within 14 days of enrollment into the study.
* History of allergy, sensitivity, or intolerance to NMDAR ligands including ketamine, dextromethorphan, memantine, methadone, dextropropoxyphene, or ketobemidone or concomitant use of such agents.
* Received another investigational drug or device within 30 days of enrollment in this study.
* Previously participated in this study.
* Psychiatric disease including major depression, bipolar disorder, anxiety, or schizophrenia, or other medical condition that, in the opinion of the investigator, would interfere with the evaluation of the study drug safety. 13) In the option of the Investigator or the Sponsor's Study Monitor, has a history of severe renal or hepatic impairment, severe active hepatic disease, or other clinically significant medical condition that may preclude safe study participation.
