Conditions: CYP2D6 Polymorphism
Allocation: NA | Intervention model: SINGLE_GROUP
Enrollment: 33
Healthy volunteers: no

Brief summary:
Specific Aim: To investigate if isotretinoin (13-cis-retinoic acid) administration decreases CYP2D6 activity in adolescent patients.

Detailed description:
In this aim, we will conduct a drug-drug interaction study evaluating the effects of 13-cis-retinoic acid on non-induced CYP2D6 activity in adolescent patients. Secondary analysis will evaluate the relationship between retinoid concentrations and CYP2D6 activity in these special populations

Arms:
arm 1: dextromethorphan pre- and post isotretinoin

Interventions: intervention 1: Isotretinoin intervention 2: dextromethorphan
Intervention descriptions: intervention 1: Drug interaction study intervention 2: Drug interaction study

Protocol document:
ICF_002.pdf: 
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UNIVERSITY OF WASHINGTON 
CONSENT FORM 
Effects of Isotretinoin on CYP2D6 Activity 
 
Researchers:  
Lead Researcher and Contact Person for Subjects: 
Mary F. Hebert, PharmD, FCCP 
Professor 
 
Pharmacy 
206-616-5016 
Coordinator: 
Alicia Stark 
 
 
 
Student Res. Assist. Pharmacy 
(360) 921-3715  
24-hour emergency telephone number:  206-598-6190 (Paging Operator), ask for Dr. Vary. 
 
Researchers’ statement 
Throughout this form we refer to ‘you’ as the subject. If you are providing permission for a 
minor to participate, ‘you’ refers to ‘your child’. We are asking you to be in a research study.  
The purpose of this consent form is to give you the information you will need to help you decide 
whether to be in the study or not.  Please read the form carefully.  You may ask questions about 
the purpose of the research, what we would ask you to do, the possible risks and benefits, your 
rights as a volunteer, and anything else about the research or this form that is not clear.  When 
we have answered all your questions, you can decide if you want to be in the study or not.  This 
process is called “informed consent.”  We will give you a copy of this form for your records. 
 
PURPOSE OF THE STUDY 
Research tells us that chemicals like vitamin A are involved in determining how the body 
handles drugs.  The purpose of this work is to see if isotretinoin, an acne medication similar to 
vitamin A, changes how the body handles dextromethorphan, a cough medication.  This study 
will include 50 patients that will be receiving isotretinoin for clinical reasons.  
 
STUDY PROCEDURES 
If you agree to participate in this study, the following will occur: 
Your medical records will be looked at and we will ask you questions to make sure you are 
eligible for the study. You may refuse to answer any question you are asked. 
If you are eligible, the study will involve 2 phases lasting up to six months.  Phase 1 will take 
place before you start isotretinoin and Phase 2 will take place while you are receiving 
isotretinoin. 
 
Phase 1 (approximately 4 ½ hours) 
For 3 days before the Phase 1 study day, you will be asked to keep track of everything you eat 
through the smart-phone application “Fooducate” or on a form that we give you.  We ask that 
you not eat grapefruit and not drink grapefruit juice during these 3 days and on your study day. 
On the 4th day, you will come to the University of Washington for a 4-hour study. 


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The study will involve you taking a single normal dose of liquid dextromethorphan by mouth.  
Dextromethorphan is a commonly used cough medication, which is available without a 
prescription.  We will give you water to drink after your dose. 
We will ask that you do not eat anything for 4 hours before the start of your study until 1 hour 
after the start of the study.  After that, we will give you a meal.  During this fasting time you are 
encouraged to drink water. 
We will measure your height, weight and wrist.  We will review your medical record and ask 
you about medications, vitamins and other things that you are taking as well as your health.  
We will have you collect a DNA sample.  These are collected by rubbing a brush, like a soft 
toothbrush, up and down on the inside of each cheek 10 times.  We will look at your genes 
involved in drug handling and response. 
We will collect all your urine over 4 hours and a single 2 tablespoons blood sample.  These 
samples will be used to look at genetic material and run tests. 
During your study and 1 week after your study, we will ask you questions to find out if you have 
any problems or complaints. 
 
Phase 2 (approximately 4 ½ hours) 
This study will not affect if you receive isotretinoin or not.  Your provider will determine if and 
how much isotretinoin you need.  After you have been on the same dose of isotretinoin for at 
least 1 week, we will ask that you come in for your Phase 2 study.   
The only adjustment in your isotretinoin is that:  
• for the 3 days before your phase 2 study, we ask that you take your isotretinoin at the same 
time everyday,  
• you take it at the time that your Phase 2 study day will start and  
• you write down the time you take each dose. 
We will check to make sure that you can still be in the study by reviewing your medical record 
and asking you questions. 
For 3 days before the Phase 2 study day, you will be asked to keep track of everything you eat 
through the smart-phone application “Fooducate” or on a form that we give you.  We will ask 
that you not eat grapefruit and not drink grapefruit juice during these 3 days and on your study 
day. 
On the 4th day, you will come to the University of Washington for a 4-hour study. 
The study will involve you taking a single normal dose of liquid dextromethorphan by mouth. 
We will give you water to drink after your dose. 
We will ask that you do not eat anything for 4 hours before the start of your study until 1 hour 
after the start of the study.  At which time we will give you a meal.  During this time, you are 
encouraged to drink water. 
We will measure your height, weight and wrist.  We will review your medical record and ask 
you about medications, vitamins and other things that you are taking as well as your health.  
We will collect all your urine over 4 hours and a single 2 tablespoons blood sample.  These 
samples will be used to look at genetic material and run tests. 


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During your study and 1 week after your study, we will ask you questions to find out if you have 
any problems or complaints. 
All remaining samples at the end of the study will be saved and shared for future research 
projects.   
[           ] 
I consent to having my leftover samples saved and shared for future research. 
[           ] 
I do NOT consent to have my leftover samples saved and shared for future research. 
Study Design Summary 
 
Phase 1 
Prior to Isotretinoin 
Phase 2 
With Isotretinoin 
Procedures 
Dextromethorphan single dose 
4-hour urine collection 
Single blood sample collection 
3-day food record 
Measure height, weight and wrist  
Check for problems or complaints  
DNA collection 
Dextromethorphan single dose 
4-hour urine collection 
Single blood sample collection 
3-day food record 
Measure height, weight and wrist 
Check for problems or complaints 
3-day isotretinoin dose record 
The total amount of time for this study is approximately 9 hours.  The total amount of blood to 
be taken for this study will be 4 tablespoons. 
 
RISKS, STRESS, OR DISCOMFORT 
Dextromethorphan Risks: 
Dextromethorphan is often used in children and teenagers.  We do not expect that you will have 
problems with a single dose.  However, if you do have problems, the most common will be mild 
dizziness, sleepiness and tiredness.   
 
Allergic reactions have been reported including rash and rarely anaphylaxis (allergy that causes 
difficulty breathing). 
 
There may be unanticipated problems from dextromethorphan. 
 
Blood Drawing Risks: 
Risks of blood drawing include pain with the needle stick, bruising and rarely fainting or 
infection. The amount of blood to be drawn for this study will not affect your blood counts. 
 
Fasting Risks: 
Risks of not eating for 4 hours before and 1 hour after dextromethorphan dosing include:  feeling 
hungry, gurgling, rumbling or growling in stomach, dizziness, faintness, headache, short-
tempered, difficulty paying attention and / or sick to your stomach. 
 
Loss of Confidentiality: 
There is a chance when you are in any study that your personal information could be accidently 
seen by someone not working on the study.  


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Other Risks: 
You will receive isotretinoin whether you are in the study or not.  Therefore, isotretinoin risks 
are not risks of this study. 
If you have study-related problems or complaints, please contact Dr. Vary through the paging 
operator at 206-598-6190 and ask for Dr. Vary and call Dr. Hebert at 206-697-2138. 
 
ALTERNATIVES TO TAKING PART IN THIS STUDY 
Taking part in this study is entirely your choice.  Choosing not to be in the study will not affect 
your isotretinoin treatment or your healthcare. 
 
BENEFITS OF THE STUDY 
There is no direct benefit to you for being in this study.  We hope the results of this study will 
help providers better care for patients needing isotretinoin.   
 
SOURCE OF FUNDING 
The study team and the University of Washington is receiving financial support for this study 
from the National Institutes of Health (NIH). 
 
CONFIDENTIALITY OF RESEARCH INFORMATION 
We will collect personal information such as your name, address, email, phone, date of birth, 
social security number and medical record number.  Coded data will be stored confidentially 
(linked to identifiers). Coded data will be stored in locked files or on password protected 
computers.  Personal identifiers will not be entered into the computer database. 
We have a Certificate of Confidentiality from the federal National Institutes of Health. This 
helps us protect your privacy. The Certificate means that we do not have to give out identifying 
information about you even if we are asked to by a court of law. We will use the Certificate to 
resist any demands for identifying information.   
 
We can’t use the Certificate to withhold your research information if you give your written 
consent to give it to an insurer, employer, or other person. Also, you or a member of your family 
can share information about yourself or your part in this research if you wish. 
 
There are some limits to this protection. We will voluntarily provide the information to: 
• a member of the federal government who needs it in order to audit or evaluate the research; 
• individuals at the University of Washington, the funding agency, and other groups involved in 
the research, if they need the information to make sure the research is being done correctly; 
• the federal Food and Drug Administration (FDA), if required by the FDA; 
• state or local authorities, if we learn of child abuse, elder abuse, or the intent to harm yourself 
or others. 
 
A description of this clinical trial will be available on http://www.clinicaltrials.gov, as required 
by U.S. law.  This Web site will not include information that can identify you. At most, the Web 
site will include a summary of the results. You can search this Web site at any time.  
Your participation in this study will be noted in your UW medical record. 


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There may also be other risks that are not yet known. 
 
DATA SHARING 
The National Institutes of Health require that federally funded studies like this study share data 
with other investigators upon request.  If requested, your data will be shared according to the 
National Institutes of Health requirements.  Only coded data will be shared.  Your identifying 
information will not be shared. 
 
OTHER INFORMATION 
You may refuse to be in and you are free to quit this study at any time without penalty or affect 
on your healthcare. 
You will be paid $100 for finishing all study procedures associated with each study phase and an 
additional $50 for finishing all study procedures.  Total payment will be $250 if all study 
procedures are completed.  Your payment for the study will be less if the study is partially 
completed.  We will need to collect your social security number to pay you. 
You will not be charged for any study related procedures. 
RESEARCH-RELATED INJURY 
If you think you have a medical problem or illness related to this research, contact Dr. Vary 
through the paging operator at 206-598-6190 and ask for Dr. Vary and call Dr. Hebert at 206-
697-2138 right away. They will treat you or refer you for treatment. 
 
 
 
Printed name of study staff obtaining consent 
Signature 
Date 
 
Subject’s statement 
This study has been explained to me.  I volunteer to take part in this research.  I have had a 
chance to ask questions.  If I have questions later about the research, or if I have been harmed by 
participating in this study, I can contact one of the researchers listed on the first page of this 
consent form.  If I have questions about my rights as a research subject, I can call the Human 
Subjects Division at (206) 543-0098.  I give permission to the researchers to use my medical 
records as described in this consent form.  I will receive a copy of this consent form. 
 
 
Printed name of subject 
 
Signature of subject  
 
 
Date 
 
When subject is a minor: 
 
 
 
Printed name of parent 
 
Signature of parent 
 
 
 
Date 
 
Copies to: 
Researcher 
 
 
Subject 
 
 
Subject’s Medical Record (if applicable) 

Prot_000.pdf: 
 
Effects of Isotretinoin on CYP2D6 Activity 
NCT03076021 
3/6/2017 
 
 


Background: 
CYP2D6 is a key drug metabolizing enzyme responsible for the metabolism of 
~25% of all drugs eliminated by the cytochrome P450 system, including clinically 
important drugs such as antiarrhythmics, opioids, cough suppressants, 
antidepressants, antipsychotics, antihypertensives, and antihistamines. As such, 
understanding CYP2D6 regulation in humans is critical not only for special populations, 
but also more broadly for patients in general.  This study will be the first step towards 
gaining insight into possible endogenous biomarkers of CYP2D6 regulation and activity 
in humans, thus moving us closer to individualized drug dosing. In the general 
population, many of these drugs have been titrated to clinical response, but there has 
been a desire to individualize therapy. Even after accounting for genotype, CYP2D6 
activity varies 4- to 30-fold in extensive metabolizers. If our hypothesis proves to be 
true, we will continue research in this area, with the goal of developing one or more 
useful biomarkers to be used in conjunction with genotype to help guide dosing of 
CYP2D6-metabolized drugs. 
 
Based on in vitro and animal studies as well as preliminary human data, we 
hypothesize that retinoic acid concentrations and retinoid signaling in the liver 
regulates CYP2D6 expression and activity in humans, which in turn contributes to 
inter-individual pharmacokinetic variability of CYP2D6 substrates.  This study will 
directly test our hypothesis by evaluating CYP2D6 activity prior to and in the presence 
of concomitant 13-cis-retinoic acid (isotretinoin) in adolescent patients.  Higher retinoic 
acid concentrations should lead to lower CYP2D6 activity. This much needed work will 
provide foundational mechanistic understanding and translate new basic science 
research findings into humans.  The administration of all-trans-retinoic acid down 
regulates CYP2D6 in the humanized mouse model. The sum of the data regarding 
retinoid regulation of CYP2D6 from in vitro studies and animal models leads us to 
believe that administration of retinoic acid will lead to decreased CYP2D6 transcription, 
expression and activity.  Since animal models are not always predictive of the effects in 
humans, it is now time to translate this work into humans. 
 
In non-pregnant adolescents, there is more than 2-fold variation in retinol 
concentrations.  Isotretinoin has been a commonly used medication in adolescent 
patients for decades as it is uniquely effective at improving severe acne.  
However, we are unable to locate any published studies evaluating the effects of 
isotretinoin on CYP2D6 activity in humans.  Some degree of acne affects almost all 
adolescents 15-17 years of age, with approximately 15–20% of teenagers developing 
moderate to severe acne. In 2000, approximately 2 million prescriptions were written for 
isotretinoin in the United States. If our hypothesis holds true, given the frequency of 
isotretinoin use in the adolescent population and the potential for interaction with 
CYP2D6 substrates, it is essential that we evaluate isotretinoin’s effect on CYP2D6 
activity and simultaneously directly test the hypothesis that retinoids play a role in 
CYP2D6 regulation in humans.  The therapeutic administration of isotretinoin 
provides us with a unique opportunity to directly explore the mechanism of 
CYP2D6 regulation by retinoic acid in humans.   
 


In summary, adolescent patients commonly experience medical conditions that require 
treatment with CYP2D6 substrates.  Although genetics play an important role in 
CYP2D6 variability, even after accounting for genetic variation, there is still a great deal 
of unaccounted variability in CYP2D6 activity.  High variability makes the utilization of 
CYP2D6 substrates challenging in this special population. With strong basic science 
data suggesting that retinoids play a key role in regulation of CYP2D6, exploring the 
relationship between CYP2D6 activity and retinoid concentrations in humans will 
provide mechanistic understanding of the variability in drug therapy, which is critical to 
the provision of individualized pharmacotherapy and the first step toward development 
of an endogenous biomarker that potentially could be used in combination with genetics 
to predict CYP2D6 activity. 
 
Objective: 
To investigate if isotretinoin (13-cis-retinoic acid) administration decreases CYP2D6 
activity in adolescent patients 
 
Design: 
Routinely at the UW Dermatology clinic, female patients with severe cystic acne who will be 
receiving isotretinoin undergo an initial evaluation, which includes laboratory tests (including a 
pregnancy test).  Thirty days later, the pregnancy test is repeated and isotretinoin is initiated at 
0.5 mg/kg/day. Twenty-eight days later, the pregnancy and laboratory tests are repeated and 
isotretinoin is increased to 1 mg/kg/day and continued for 3-4 months.  Pregnancy and 
laboratory tests are repeated every 28 days.  A similar protocol is followed for the male patients, 
excluding the pregnancy tests. The timing of our proposed study will fit into routine clinical visits 
and enhance the ease and success of study conduct.
 
 
Study Design 
This is a prospective, pharmacokinetic study of oral dextromethophan in adolescent patients.  
The study will be divided into 2 phases.  Phase 1 will occur prior to initiation of isotretinoin and 
involve a single dose of oral dextromethorphan. Phase 2 will occur ≥ 1 week after initiation of 
steady-state isotretinoin and will repeat the single oral dose of dextromethorphan.   Each 
subject will serve as his or her own control.  All studies will be performed at the University of 
Washington. 
 
 
Experimental Methods:   
4.3.3. Study Design Summary:  
Test 
Phase 1 
Pre-isotretinoin 
Phase 2 
Concomitant Isotretinoin 
CYP2D6 genotype (pre-DM study) 
X 
 


Dextromethorphan single 30 mg oral dose 
X 
X 
Concomitant steady state isotretinoin 
administration 
 
X 
4-hour urinary DM/DX MR 
X 
X 
Total plasma all-trans retinoic acid, 13-cis-
retinoic acid, retinol (all-trans and 13-cis), 
retinyl palmitate, 4-oxo-all-trans retinoic acid, 4-
oxo-13-cis-retinoic acid and retinol binding 
protein concentrations 
X 
X 
Serum creatinine, BUN, ALT, bilirubin, albumin 
X 
X 
Urine creatinine and pH 
X 
X 
4.3.4. Dextromethorphan administration: Following a ≥4 hour fast, subjects will receive DM 
(alcohol free) 30 mg orally on each study day.  DM was selected as our CYP2D6 probe because 
it is a standard probe for CYP2D6 activity and has a well-established safety record in 
adolescent patients and children.(4,131-134)  
4.3.5. Isotretinoin administration:  Isotretinoin administration will follow routine clinical 
practice.  Isotretinoin administration will not be altered for research purposes. The Phase 2 
study with concomitant isotretinoin will take place once patients have been taking oral 
isotretinoin 1 mg/kg/day for ≥ 1 week.  If the patient does not tolerate 1 mg/kg/day and is 
reduced to 0.5 mg/kg/day as their final isotretinoin dose, then ≥ 1 week after starting that dose, 
subjects will complete their Phase 2 study.  Subjects receiving higher doses will also be 
included. We will attempt to study all subjects while receiving ~1 mg/kg/day, but recognize that 
some patients might require higher or lower doses and will be studied on their clinically 
indicated dose. 

SAP_001.pdf: 
Effects of Isotretinoin on CYP2D6 Activity 
NCT03076021 
3/6/2017 
 
 


 
Dextromethorphan/dextrorphan metabolic ratio: All urine will be collected over 4 hours 
following DM administration for measurement of our endpoint, urinary DM/DX MR, as previously 
described.  Urine pH will also be measured.  We recognize that urinary DM/DX MR is influenced 
by renal clearance (blood flow, secretion and filtration), changes in CYP3A activity or changes in 
urine pH.  Urine samples will be analyzed for DM, DX, 3-methoxymorphinan, 3-
hydroxymorphinan and DX-O-glucuronide concentrations using our validated UHPLC-MS/MS 
assay. 
 
CYP2D6 genotype:  Buccal swabs will be collected from each subject for CYP2D6 genotyping 
prior to the first DM study.  The following CYP2D6 genotypes will be determined:  CYP2D6*3 
(2549delA), CYP2D6*4 (1846G>A), CYP2D6*5 (CYP2D6 deleted), CYP2D6*6 (1707delT), 
CYP2D6*9 (2613 delAGA), CYP2D6*10 (100C>T), CYP2D6*17 (1023C>T), CYP2D6*35 (-1584 
C>G and 31G>A) and CYP2D6*41 (2988 G>A) as previously described using commercially 
available TaqMan assays.  The genotype will be used to predict the subject phenotype (PM, IM, 
EM or UM) as well as activity scores (0, 0.5, 1,1.5, 2 and 3) as described previously.   Only 
extensive metabolizers with index scores based on genotype of 1,1.5 and 2 will proceed with 
the DM portion of the study. 
 
DX/DM MRs were calculated by dividing the molar quantity (urine) of the metabolite by that of 
the parent. DX plus DX-O-glucuronide/DM urinary MR was calculated by dividing the sum of the 
molar quantity of metabolites by that of the parent. Urine samples with concentrations above or 
within 5% of the LLOQ were accepted, and concentrations lower than that were excluded from 
data analysis. DX/DM and DX plus DX-O-glucuronide/DM MRs were analyzed only in CYP2D6 
EMs (AS = 1-2). The GMR and 90% CI were used to compare urinary MRs between study 
timepoint 1 (pre-treatment control) and study timepoint 2 (with isotretinoin treatment). The 90% 
CI of the GMR for the MR with isotretinoin treatment over pre-treatment control was compared 
to the bioequivalence range of 0.8 and 1.25 according to FDA Guidance of Clinical Drug 
Interaction Studies.  If the 90% CI does not include 1, there is an indication of a potential drug 
interaction. Statistical analyses were all conducted on GraphPad Prism 9.5.1 (GraphPad 
Software, Inc., La Jolla, CA, USA).