Role of CYP2B6 Polymorphisms in Ketamine Metabolism and Clearance
Phase: NA
Conditions: Healthy Volunteers
Sponsor: Washington University School of Medicine

RESEARCH PROTOCOL 
 
 
 
 
 
 
 
Role of CYP2B6 polymorphisms in ketamine metabolism and clearance  
 
 
 
 
 
 
 
Evan D. Kharasch, M.D., Ph.D. 
Russell D. and Mary B. Shelden Professor of Anesthesiology 
Director, Division of Clinical and Translational Research 
Washington University School of Medicine 
Department of Anesthesiology 
660 S. Euclid Ave., Campus Box 8054 
St. Louis, Mo. 63110 
Voice: (314) 362-8796 
Fax: (314) 747-3371 
E-mail: kharasch@wustl.edu 
 
 
 
 
 
Original Version: July 9, 2013 
 
 
 

2 
 
CONFIDENTIAL: This document is the intellectual property of Evan Kharasch, MD, PhD. Acceptance of this document 
constitutes agreement by the recipient that no unpublished information contained herein will be published or disclosed 
without prior written approval. 
1.  SYNOPSIS 
 
Study Title 
Role of CYP2B6 polymorphisms in ketamine metabolism and clearance  
Objective 
To determine the effects of cytochrome P4502B6 (CYP2B6) genetic variants on 
ketamine metabolism and clearance  
Study Design 
Single-center, open label, single-session study to evaluate ketamine pharmaco-
kinetics in subjects with known CYP2B6 genotype  
Study Period 
Planned enrollment duration: Approximately 3 months.  Planned study duration: 
1 day per subject 
Number of Patients Approximately 40 healthy volunteers identified by CYP2B6 genotyping by 
HRPO-approved screening 
Inclusion and 
Exclusion Criteria 
Inclusion Criteria 
a) 18-50 yr old 
b) CYP2B6*1/*1, CYP2B6*1/*6 or CYP2B6*6/*6 genotype 
c) Good general health with no remarkable medical conditions  
d) BMI < 33 
e) Provide informed consent 
Exclusion Criteria 
a) Known history of liver or kidney disease 
b) Use of prescription or non-prescription medications, herbals, foods or 
chemicals known to be metabolized by or affecting CYP2B6  
c) Females who are pregnant or nursing 
d) Known history of drug or alcohol addiction (prior or present addiction or 
treatment for addiction) 
e) Direct physical access to and routine handling of addicting drugs in the 
regular course of duty (a routine exclusion from studies of drugs with 
addiction potential) 
Study Medication 
Administration 
Subjects will be studied on one occasion at Washington University in St. Louis 
School of Medicine for administration of study drugs and blood collection.  
Study drug is oral ketamine HCl solution (0.4 mg/kg) 
Measurements 
Plasma samples are obtained for 12 hr after ketamine for measurement of parent 
drug and metabolite concentrations.  A 24hr urine collection is also obtained.  
Subjective self-assessment of ketamine effect is performed using visual or verbal 
analog scales.  Ketamine and metabolite concentrations are determined by 
stereoselective LC-MS/MS. 
Outcomes 
Primary:  Plasma norketamine/ketamine AUC ratio 
Secondary:  Plasma ketamine enantiomers and metabolite AUC, maximum 
concentration, apparent oral clearance, and metabolite formation clearances.  
Influence of CYP2B6*6 hetero or homozygote genotype on above primary and 
secondary outcomes 
 
 
 

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CONFIDENTIAL: This document is the intellectual property of Evan Kharasch, MD, PhD. Acceptance of this document 
constitutes agreement by the recipient that no unpublished information contained herein will be published or disclosed 
without prior written approval. 
2.  STUDY PROTOCOL 
 
2.1 Background and Significance 
 
Ketamine is a noncompetitive NMDA receptor antagonist, originally developed in 1964 as a 
"dissociative" anesthetic, and FDA approved in 1970.  It can be administered by intravenous, 
intramuscular, oral, sublingual, intranasal, and rectal routes.  Ketamine has been widely used for decades 
in anesthesia, in part, because unlike most other intravenous anesthetics, it does not significantly depress 
the respiratory and circulatory systems.  In addition, ketamine causes significant anti-nociceptive and 
anti-hyperalgesic (i.e. analgesic) effects at low doses – lower than those which cause loss sedation and 
loss of consciousness. 
 
More recently, there has been marked interest in the use of ketamine for other applications.  Oral 
ketamine has been evaluated extensively for use in chronic pain management.1  Use in pediatric sedation, 
analgesia, and emergency room analgesia is also of interest.2-5  More recently, has been the discovery that 
ketamine may be effective in the therapy of treatment-resistant depression, and with very fast response 
rates.6-9  A review of clinicaltrials.gov reveals a plethora of recent studies on ketamine.  Thus there is very 
active research and clinical interest in ketamine. 
 
Ketamine is administered clinically as a racemic mixture (R- and S-ketamine).  Ketamine undergoes 
extensive metabolism, primarily via N-demethylation to norketamine, and to several other metabolites.10-
13  First-pass metabolism of oral ketamine is considerable, thus it is only about 30% bioavailable.  There 
are stereoselective differences in ketamine enantiomers metabolism and disposition.  It has recently been 
established that cytochrome P4502B6 (CYP2B6) is the major isoform catalyzing ketamine N-
demethylation in vitro, at therapeutic concentrations.14-16  A recent clinical investigation confirmed the 
predominant role of CYP2B6, and lack of significant CYP3A involvement, in ketamine pharmacokinetics 
and metabolism.17  
 
CYP2B6 is a highly polymorphic enzyme.18  The most common variant allele, CYP2B6*6, found most 
commonly in Africans, Africans-Americans, and some Asian populations, is associated with diminished 
hepatic CYP2B6 enzyme expression. Compared with wild-type CYP2B6*1/*1.  A recent in vitro 
investigation demonstrated that CYP2B6.6 (the protein encoded by the CYP2B6*6 allele) has diminished 
catalytic activity towards ketamine N-demethylation (compared with wild-type CYP2B.1, and liver 
microsomes from humans heterozygous or homozygous for the CYP2B6*6 allele also had diminished 
catalytic activity towards ketamine N-demethylation, compared with CYP2B6*1/*1.16 
 
Nonetheless, there is no formal evaluation of ketamine pharmacokinetics, metabolism or clearance in 
CYP2B6*6 carriers.  This investigation will formally address the role of CYP2B6 polymorphism in 
ketamine disposition. The research proposed will test the hypothesis that CYP2B6 variants (CYP2B6*6 
hetero or homozygotes) in vivo will have decreased ketamine metabolism and clearance. 
 
2.2 Objective  
Determine the influence of CYP2B6 genetic variation, specifically CYP2B6*6 polymorphism, on 
ketamine metabolism and clearance.  Other, rare genotypes may be enrolled as a secondary objective.  
 
2.3 Patient Selection 
Subjects will be recruited from the greater St. Louis community that has been identified as carriers of 
CYP2B6 polymorphisms (identified by participation in Washington University HRPO approved study 
HRPO#201203033).  Thirty evaluable, healthy male and non-pregnant female 18-50 yr volunteers, in 
approximately equal sex distribution, will be studied.  Minorities will be actively sought and included, 
with minority composition to reflect that of the greater Washington University/St. Louis community. 

4 
 
CONFIDENTIAL: This document is the intellectual property of Evan Kharasch, MD, PhD. Acceptance of this document 
constitutes agreement by the recipient that no unpublished information contained herein will be published or disclosed 
without prior written approval. 
2.3.1 Inclusion Criteria 
Each subject must meet all of the following criteria: 
a) 18-50 yr old 
b) CYP2B6*1/*1, CYP2B6*1/*6 or CYP2B6*6/*6 genotype (see table)  (Note:  subjects of other rare 
genotype but with one or more 516G>T, 785A>G, 983T>C or 1459C>T polymorphism may be 
enrolled at PI’s discretion) 
c) Good general health with no remarkable medical conditions 
d) BMI <33 
e) Provided informed consent 
 
Allele 
Protein 
cDNA Change 
Amino acid change 
Enzyme 
activity 
 
CYP2B6*4 
CYP2B6.4 
785A>G 
K262R 
 Incr. 
Lang et al., 2001; 
Kirchheiner 
et 
al., 
2003 
CYP2B6*5 
CYP2B6.5 
1459C>T 
R487C 
  
Lang et al., 2001 
CYP2B6*6 
CYP2B6.6 
516G>T; 785A>G 
Q172H; K262R 
Decr. expr 
Lang et al., 2001; 
Tsuchiya et al., 2004; 
Hofmann et al., 2008 
CYP2B6*7 
CYP2B6.7 
516G>T; 785A>G; 1459C>T 
Q172H; K262R; R487C 
  
Lang et al., 2001 
CYP2B6*9 
CYP2B6.9 
516G>T 
Q172H 
  
Lamba et al., 2003 
CYP2B6*13 CYP2B6.13 415A>G; 516G>T; 785A>G 
K139E; Q172H; K262R 
Decr.? 
Lang et al., 2004 
CYP2B6*16 CYP2B6.16 785A>G; 983T>C 
K262R; I328T  
Decr. expr. Wang et al., 2006 
CYP2B6*18 CYP2B6.18 983T>C 
I328T  
Decr. expr. Klein et al., 2005 
CYP2B6*19 CYP2B6.19 516G>T; 785A>G; 1006C>T 
Q172H; K262R; R336C 
Decr. expr. Klein et al., 2005 
CYP2B6*20 CYP2B6.20 503C>T; 516G>T; 785A>G 
T168I; Q172H; K262R  
Decr. expr. Klein et al., 2005    
CYP2B6*26 CYP2B6.26 499C>G; 516G>T; 785A>G 
P167A; Q172H; K262R 
Decr  
Gatanaga et al., 2007 
 
2.3.2 Exclusion Criteria 
Subjects will not be enrolled if any of the following criteria exist: 
a) Known history of liver or kidney disease 
b) Use of prescription or non prescription medications, herbals, foods or chemicals known to be 
metabolized by or affecting CYP2B6  
c) Females who are pregnant or nursing 
d) Known history of drug or alcohol addiction (prior or present addiction or treatment for addiction) 
e) Direct physical access to and routine handling of addicting drugs in the regular course of duty 
(this is a routine exclusion from studies of drugs with addiction potential) 
 
2.4 Design and Procedures 
 
2.4.1 Study Design 
Single-center, open-label, single-session study.  The study population will be thirty evaluable healthy 
male and nonpregnant female 18-50 yr volunteers.  All subjects will undergo the same study procedures. 
 
2.4.2 
Minimization of Bias 
Placebo control and double-blinding are not required.  Plasma drug concentration is not influenced by 
subjects’ or investigators’ knowledge of study aims and hypotheses.  Results will be coded by enrollment 
number, such that pharmacokinetic data analysis will be blinded as to subjects’ genotype group. 
 
 
 

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CONFIDENTIAL: This document is the intellectual property of Evan Kharasch, MD, PhD. Acceptance of this document 
constitutes agreement by the recipient that no unpublished information contained herein will be published or disclosed 
without prior written approval. 
2.4.3  Pre-Study Period 
Subjects who are potential candidates for the study will be educated as to the study procedures, benefits, 
and potential risks.  They will fill out a health self-assessment, including a structured interview to screen 
for history of substance abuse or addiction.  Each subject who qualifies for entry into the study on the 
basis of inclusion/exclusion criteria, prestudy evaluations and completion of an informed consent will be 
assigned the next available patient number.  This indicates enrollment in the study.  Weight will be 
recorded.  A urine HCG pregnancy test for women of childbearing potential will be performed on the 
study day prior to study drug administration.  Subjects who drop out of the study prior to completing the 
study will be replaced by using the next available patient number. 
 
2.4.4  Study Period 
Subjects will be required to refrain from: 1) alcohol for 48 hr prior to and during study days, 2) caffeine-
containing beverages the day of study drug administration, 3) no grapefruit, oranges or apples or their 
juices for 5d prior to the study day, 4) food/liquids after midnight the day prior to drug administration (to 
eliminate food influence on oral drug absorption), 6) non-study medications (including over the counter 
and/or herbal), for 3d prior to study visit, without prior PI approval. 
 
Subjects will be studied at Washington University in St. Louis School of Medicine.  The study day will 
consist of an approximately 12.5-13 hr stay for drug administration, blood sampling, and urine collection.  
Subjects will be given a container to take home and continue their urine collection, and return the next 
morning to return their 24 hr urine collection.   
 
Subjects will have a peripheral IV catheter inserted for blood sampling.  Subjects are then administered 
0.4 mg/kg oral racemic ketamine with 200cc water.  At various time points, up to 12 hours after drug 
administration, venous blood samples will be drawn.  Typical sampling (5cc) will be before, and 0.25, 
0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 10, 12 hr after ketamine (13 samples, 65 ml).  Coincident with blood 
sampling, subjective self-assessment of drug effect is performed using visual or verbal analog scales 
(scored from 0 to 100) for levels of alertness/sedation (almost asleep to wide awake), energy level (no 
energy to full of energy), confusion (confused to clear headed), clumsiness (extremely clumsy to well-
coordinated), anxiety (calm/ relaxed to extremely nervous), and nausea (no nausea to worst nausea). 
 
Two hours after dosing is completed subjects will be free to move around and be given a standard meal. 
Subjects will have free access to food and water during the study session and other meals will be provided 
during the day.  At the end of the session the IV catheter is removed and subjects go home.  
Transportation home will be provided if required.   
 
2.4.5 Study Drug and Doses 
ketamine HCl solution (0.4 mg/kg administered orally).  This is equivalent to about 0.1-0.15 mg/kg IV.   
 
Drugs will be obtained from commercial sources or the Barnes-Jewish Hospital investigational pharmacy.  
 
2.5  Observations and Measurements 
 
2.5.1 Drug and metabolite concentrations  
Plasma and urine concentrations of ketamine and metabolites are determined by LC-mass spectrometry 
using stereoselective methods developed and currently implemented in the PI’s lab. 
 
2.5.2 Calculations 
Area under the curve (AUC) of plasma ketamine concentration is determined by noncompartmental 
methods using nonlinear regression analysis.  Clearance is dose/AUC.  
 

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CONFIDENTIAL: This document is the intellectual property of Evan Kharasch, MD, PhD. Acceptance of this document 
constitutes agreement by the recipient that no unpublished information contained herein will be published or disclosed 
without prior written approval. 
2.5.3 Primary Outcome Measure 
Ketamine metabolism, measured as plasma norketamine/ketamine concentration-time AUC0- ratio, by 
CYP2B6*6 hetero or homozygote genotype. 
 
2.5.4 Secondary Outcome Measures 
1) ketamine enantiomers area under the plasma concentration curve (AUC0-∞), maximum plasma 
concentration, apparent oral clearance (and by CYP2B6*6 hetero or homozygote genotype) 
2) norketamine enantiomers formation clearances (and by genotype) 
 
2.5.5   Statistical Methods 
Plasma and urine ketamine and metabolite concentrations are analyzed by noncompartmental methods. 
Outcome measures in wild-type and CYP2B6*6 carriers will be evaluated by ANOVA.  If the hypothesis 
is correct, we will observe diminished ketamine metabolism and clearance in CYP2B6*6 carriers.   
 
2.5.6   Sample Size 
This is a pilot study.  We plan to study 30 evaluable subjects, assembled by CYP2B6 genotyping, 
described previously (HRPO#201203033), to compose groups of 10 wild-type (CYP2B6*1/*1), 10 
CYP2B6 heterozygotes (CYP2B6*1/*6) and 10 CYP2B6*6 homozygotes (CYP2B6*6/*6). 
 
3.0 Management of Intercurrent Events 
 
3.1 Adverse Experiences 
The investigator will closely monitor subjects for evidence of adverse events.  All adverse events will be 
reported and followed until satisfactory resolution.  The description of the adverse experience will include 
the time of onset, duration, intensity, etiology, relationship to the study drug (none, unlikely, possible, 
probable, highly probable), and any treatment required. 
 
3.2 Premature Discontinuation 
If a subject withdraws from the study, the subject will be replaced in order to provide the required number 
of subjects.  Subjects will be withdrawn if the investigator decides that discontinuation is in the best 
interest of the subject, or the subject requests withdrawal from the study. 
 
3.3 Potential Risks 
 
3.3.1 Potential risks from ketamine  
Oral ketamine has been reported to produce fewer and milder adverse effects than parenteral ketamine, 
because lower peak plasma levels are reached after oral intake, there is extensive first-pass metabolism, 
the main metabolite norketamine reaches higher plasma levels, and norketamine might have a more 
favorable safety profile than ketamine.1  The most frequently observed adverse effects of oral ketamine 
reported (across a range of doses) were effects on the central nervous system, such as sedation, 
somnolence, dizziness, sensory illusions, hallucinations, nightmares, dissociative feeling and blurred 
vision.  Qualitatively similar adverse effects in patients were seen with intramuscular (0.4 mg/kg) and oral 
(4 mg/kg) ketamine, but there were fewer side-effects in the latter group, suggesting that adverse effects 
of oral ketamine are about one tenth that of intravenous ketamine.  No distinction was made between 
effects of a single dose and effects after long term dosing.1  Adverse effects of ketamine (0.1 mg/kg IV) in 
healthy volunteers were minimal.19  Based on prior experience with ketamine, the dose proposed (0.4 
mg/kg oral, equivalent to 0.1-0.15 mg/kg IV), and prior published experience, some subjects may 
experience very mild drowsiness for about 1-2 hr after ketamine administration.  As a precaution, 
volunteers are kept under observation if pharmacologic effects are present, and they are admonished to 
neither drive nor operate dangerous machinery for the remainder of the study day.  Overall the risks 
associated with the use of ketamine in healthy volunteers are very small. 

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CONFIDENTIAL: This document is the intellectual property of Evan Kharasch, MD, PhD. Acceptance of this document 
constitutes agreement by the recipient that no unpublished information contained herein will be published or disclosed 
without prior written approval. 
3.3.2  Other Potential Risks 
Intravenous catheter placement can cause a bruise.  The amount of blood drawn will not constitute a risk 
to subjects, since sessions are carefully timed to prevent phlebotomy from exceeding recommended 
limits.  No psychological risks to subjects are envisioned.  
 
3.4  Procedures to Minimize Potential Risks 
The ketamine dose to be studied is subanesthetic, less than the recommended starting dose (0.5 mg/kg) for 
oral therapy in ketamine-naïve patients, and commensurate with that currently used in clinical studies 
(clinicaltrials.gov).  Studies are conducted in the Washington University Department of Anesthesiology 
Research Unit under the general supervision of the PI, a board-certified anesthesiologist thoroughly 
trained and experienced in the administration of drugs, assessment of adverse effects, and their treatment.  
Subjects are monitored by trained (RN) nursing personnel.  A urine pregnancy test will be performed on 
women of childbearing potential and subjects excluded if pregnant.  Subjects will be informed that 
participation is voluntary and they may refuse to participate and may withdraw from the study at any time 
without penalty.  Subjects will be told that in the event of a physical injury as the direct result of study 
procedures, they will be cared for by a member of the investigating team at no cost, within the limits of 
the Washington University compensation plan. 
 
3.5   Data and Safety Monitoring Plan 
The monitoring plan has been specifically developed to maximize research participant safety and for the 
protocols planned herein.  In general, the PI has developed a specific set of Standard Operating 
Procedures (SOPs) for clinical research.  All individuals working under the PI are required to read, be 
familiar with, and compliant with the SOPs.  The specific monitoring plan for this investigation is 
commensurate with the risks and the size and complexity of the investigations planned.  These risks, as 
described above, are small.  The basic clinical protocol design has been used previously by the PI in 
hundreds of subjects, and the response to the drugs, adverse events (essentially only nausea and vomiting 
with opioids) and potential risks are well-characterized and well-known to the PI.  Based on these 
considerations, we utilize a monitoring plan that involves:  
(1) engaging a colleague not involved in the study to serve in a monitoring capacity.  Based on the small 
size and low-risk, we envision only a third person (the colleague), not a full DSMB. 
(2) a specific plan for submitting Adverse Event Reports to the IRB.  That plan is detailed in the PI's SOP 
for Adverse Event Reporting (attached). 
 
4.  HUMAN SUBJECTS RESEARCH 
 
4.1 Protection of Human Subjects 
This study will involve normal subjects, whose participation will be strictly voluntary.  This study is not a 
clinical trial which is designed to assess the safety and/or efficacy of drugs, devices, diagnostics, 
treatments, or preventive measures in humans for the treatment of any disease.  The study will be covered 
under appropriate Washington University Institutional Review Board protocols and consent forms.  The 
study will be conducted under the supervision of the PI, a Board-Certified and GCP-certified 
anesthesiologist with several years experience in the conduct of human volunteer studies. 
 
4.2 Sources of Materials 
For studies involving healthy volunteers, no medical records are used.  Data on health and medication use 
are provided by subjects who fill out a health status questionnaire.  Specimens include blood obtained 
exclusively for research purposes.   
 
4.3 Recruitment and Informed Consent 
Subjects will be approached for participation from a cohort of individuals previously genotyped for 
CYP2B6 (HRPO approved protocol #201203033), in which subjects provide written consent for contact 

8 
 
CONFIDENTIAL: This document is the intellectual property of Evan Kharasch, MD, PhD. Acceptance of this document 
constitutes agreement by the recipient that no unpublished information contained herein will be published or disclosed 
without prior written approval. 
and recruitment for additional research studies.  Subjects with specific genotypes (CYP2B6*1/*1, 
CYP2B6*1/*6 or CYP2B6*6/*6) will be invited to participate in this protocol.  Subjects will be provided 
verbal and written descriptions of the study aims, procedures, risks, and benefits, and will be required to 
give written informed consent.  A member of the investigative team provides all study descriptions, 
informed consent, and answers all questions.  No deception is required for the purposes of this study.  
Subjects are informed verbally and in writing that participation is voluntary and they may refuse to 
participate and may withdraw from the study at any time without penalty. 
 
4.4 Potential Benefits of the Proposed Research to the Subjects and Others 
There is no benefit to individual subjects in this study.  Society may benefit from a better understanding 
of ketamine metabolism, drug interactions and pharmacokinetics, leading to improved practice standards 
among clinicians. 
 
4.5 Inclusion of Women 
Studies and their advertisements actively encourage the participation of women in the research.  As a 
matter of operational policy, our studies of healthy volunteers routinely and deliberately include 
equivalent numbers of women and men. To ensure sufficient enrollment of women, we typically close 
enrollment to men once their quota has been filled.  This approach has been highly successful.  Women of 
childbearing potential are not excluded from our research protocols.  Pregnancy testing is performed as a 
matter of course to protect female research subjects, and subjects are instructed when appropriate to use 
adequate contraceptive measures. 
 
4.6 Inclusion of Minorities 
All of our studies and their advertisements actively encourage the participation of minorities in research.  
Our minority recruiting typically matches the demographic composition of the Washington University 
community from which subjects will be recruited (78% white, 21% Black, <1 % Hispanic).   However, 
based on the higher incidence of CYP2B6*6 allele in African-Americans, we anticipate a higher 
enrollment of minorities related to increased incidence of genotype.  
 
4.7 Inclusion of Children 
Children <18 yr will not be studied in this pilot investigation because there is no direct benefit to them, 
and the study aims address only adults. 
 
 
5.  REFERENCES 
 
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CONFIDENTIAL: This document is the intellectual property of Evan Kharasch, MD, PhD. Acceptance of this document 
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without prior written approval. 
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