• 1) 17-item total severity Clinician Administered PTSD Scale (CAPS); change in scores from baseline to endpoint
• 2) % or patients with treatment response measured by CGI-I (1=very much improved; 2= much improved) and CGI-Severity

• Additional rating scales [ Time Frame: Measured weekly throughout the study ] [ Designated as safety issue: No ]
• CSF levels of norepinephrine (NE) and NE metabolites, as measured by lumbar puncture [ Time Frame: Measured at baseline and end of treatment ] [ Designated as safety issue: No ]
• Hippocampal volume, as measured by volumetric MRI [ Time Frame: Measured at baseline and end of treatment ] [ Designated as safety issue: No ]
• Adverse Event Rating [ Time Frame: Measured weekly throughout the study ] [ Designated as safety issue: Yes ]

• 1) Additional rating scales; changes from baseline to endpoint
• 2) Subgroup analyses of effects of demographic and clinical characteristics on treatment outcome.
• 3) CSF levels of norepinephrine (NE) and NE metabolites, as measured by lumbar puncture before and after the trial.
• 4) Hippocampal volume, as measured by volumetric MRI before and after the trial.

This study will evaluate the effectiveness of the Nk1 antagonist, GR205171, as compared to placebo, in improving overall PTSD symptoms.

This is a 10-week, double-blind, placebo-controlled trial of an NK1 antagonist, GR205171, in post traumatic stress disorder.

The purposes of the study are:

1. To measure the effectiveness of the study drug, GR205171, as compared to placebo, in improving overall PTSD symptoms.
2. To determine whether neurobiological markers, as measured through pre and post-study MRI and lumbar puncture, can predict the effectiveness of GR205171 in PTSD patients.

People with PTSD between the ages of 18 and 65 may be eligible for this study. Potential participants receive a thorough psychiatric and medical screening, and if found eligible, enter into the 10-week trial. Participants must be free of psychotropic medications for at least 2 weeks prior to the beginning of the 10 weeks.

There are weekly in-person visits throughout the study, where study physicians evaluate the participant's progress and monitor the occurrence of side effects, and participants have blood drawn for safety lab tests.

Participants have the option of participating in an MRI and lumbar puncture both during the first 2 weeks of the study and at the end of the 2 weeks.

Post-traumatic stress disorder (PTSD) is a chronic and common anxiety disorder that follows exposure to an overwhelming traumatic event. The majority of patients with PTSD also meet criteria for other psychiatric disorders, and many attempt suicide. Despite its impact on society, little is known about the etiology or pathophysiology of this disorder. PTSD is responsive to pharmacological treatments such as selective serotonin reuptake inhibitors (SSRIs), but response rates rarely exceed 60%, and even fewer patients (20-30%) achieve clinical remission. Thus, there is a clear need to develop novel and improved therapeutics for PTSD.

A growing body of preclinical studies suggests that activation of substance P (SP) and its NK1 receptor is anxiogenic and that NK1 antagonists, with chronic administration, exert significant dampening effects on this system. SP is a neuropeptide belonging to the tachykinin family, and has been implicated in several neurological and psychiatric illnesses. Excess activity of the SP-NK1 system thus stands as a prime candidate for involvement in the pathophysiology of anxiety disorders such as PTSD.

We propose to investigate the efficacy of the highly specific NK1 antagonist GR205171 in PTSD in a placebo-controlled clinical trial. Furthermore, we propose to investigate whether certain biological surrogate markers (neuroendocrine and neuroimaging) are predictive of treatment response. If a patient is already taking medication for PTSD and has achieved therapeutic response, he/she will not be tapered off effective medication(s) to participate in this study, and will not be eligible for the study. Taper and discontinuation of medications in preparation for this study will only occur in those patients who are not responding to medication treatment for PTSD.

Hypotheses:

1. PTSD patients randomized to the NK1 antagonist GR205171 will achieve higher response rates acutely compared to patients randomized to placebo.
2. Biological surrogate makers involving neuroendocrine (CSF SP and NE) and neuroimaging function will be predictive of treatment response.

• Stress Disorders
• Post-Traumatic Stress Disorder

• Drug: NK1 antagonist GR205171
• Drug: Placebo

• Placebo Comparator: Participants will take placebo
• Experimental: Participants will take the study drug GR205171

Inclusion Criteria:

• Diagnosed with PTSD (as determined by the initial evaluation) that has lasted for at least 3 months prior to study entry
• A negative urine toxicology during screening
• Females willing to use an effective form of birth control throughout the study

Exclusion Criteria:

• Current diagnosis of schizophrenia, a psychotic disorder, bipolar disorder, or other psychiatric disorder except for depression secondary to the PTSD
• Participation in a clinical trial of a new drug within 4 months of study entry or any other trial within 3 months of study entry
• Current evidence or history of serious unstable medical illness or organic brain impairment, including stroke, brain tumor, demyelinating disease, heart, lung, stomach, kidney, or liver impairment
• Serious suicidal or homicidal risk
• Substance abuse or dependence within 90 days of study entry
• Use of effective psychiatric medications within 2 weeks of study entry or use of Prozac within 5 weeks of study entry
• Current treatment with any other medication other than those approved by study physicians
• Consumption, on average, of more than 4 drinks/day per week, if male, of more than 3 drinks/day per week if female
• Donation of a unit (450ml) of blood within the previous month or intent to donate blood within one month of completing the study;
• Pregnant or breastfeeding
• Previous treatment with an NKI antagonist