This webinar will focus on recent scientific and regulatory developments impacting the design of clinical drug-drug interaction studies.

1. WHAT’S NEW IN CLINICAL DRUG-DRUG
INTERACTION STUDIES:
RECOMMENDATIONS FROM REGULATORY AUTHORITIES AND
SCIENTIFIC CONSORTIA

2. M A K I N G T H E C O M P L E X S E A M L E S S
General interest to scientists in
drug development
Clinical pharmacologists
DDI experts
Timing of DDI investigations?
Which species to study?
When can in vitro data be utilized in place of clinical studies?
Which enzymes and transporters should be evaluated?
What are the advantages of a cocktail study?
When is a microdosing study appropriate?
What is new in selection of probe drugs?
‒ Which CYP3A4 inhibitor?
‒ Which P-gp substrate?
What are the current recommendations for study designs?
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3. M A K I N G T H E C O M P L E X S E A M L E S S
Accessed 11/02/17 https://www.fda.gov/regulatory-information/search-fda-
guidance-documents/vitro-metabolism-and-transporter-mediated-drug-drug-
interaction-studies-guidance-industry
Accessed 11/02/17 https://www.fda.gov/regulatory-information/search-fda-guidance-
documents/clinical-drug-interaction-studies-study-design-data-analysis-and-clinical-
implications-guidance
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4. M A K I N G T H E C O M P L E X S E A M L E S S
Cortellis for Competitive Intelligence (downloaded September 2018), Notification:
PSEHB/PED No 0723/4 : Guideline of Drug Interactions for Pharmaceutical
Development and Information Provision, Revision, 23-Jul-2018 (English and Japanese
versions)
Accessed 09/13/2019 from https://www.ema.europa.eu/en/documents/scientific-
guideline/guideline-investigation-drug-interactions_en.pdf
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5. M A K I N G T H E C O M P L E X S E A M L E S S
DRUG-DRUG INTERACTIONS ARISING FROM
CHANGES IN METABOLISM & TRANSPORT
• Enzymes and transporters behave predictably – transition from studying specific
drug pairs to systematically evaluating changes in PK with index drugs in order
generalize the interaction potential with a much broader list of drugs
• Significant step forward in improving drug safety
• Additional payoff to sponsors is the potential to eliminate some clinical DDI trials
• Qualitative estimations
‒ Decision trees
‒ Physiologically based Pharmacokinetic Modeling (PBPK)
• Quantitative estimations
‒ PBPK– predict and simulate magnitude of interactions, evaluate impact of intrinsic and
extrinsic factors
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Empirical Mechanistic

6. M A K I N G T H E C O M P L E X S E A M L E S S
Draft Guidance for Industry; Drug Interaction Studies – Study Design, Data Analysis, Implications for Dosing and Labeling Recommendations. 2012 https://www.regulations.gov/document?D=FDA-2006-D-0036-0032.
Example of Decision Tree
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7. M A K I N G T H E C O M P L E X S E A M L E S S
EXAMPLE: QUALITATIVE USE OF IN VITRO DDI DATA
IN PRODUCT LABELING
Ruzurgi® (amifampridine) indicated for the treatment of Lambert-Eaton
myasthenic syndrome (LEMS) in patients 6 to less than 17 years of
age” (approved May 2019)
“In vitro studies with human liver microsomes indicated that
amifampridine and 3-N-acetyl amifampridine were not direct or time-
dependent inhibitors of CYP1A2, CYP2A6, CYP2B6, CYP2C8,
CYP2C9, CYP2C19, CYP2D6, CYP2E1, or CYP3A4. In vitro studies in
cryopreserved human hepatocytes indicated that amifampridine did not
induce CYP isoforms CYP1A2, CYP2B6, or CYP3A4. Based on in vitro
studies with Caco-2 cells amifampridine is unlikely to act as a substrate
or inhibitor of the P glycoprotein transporter. Amifampridine is not an
inhibitor of the BCRP transporter.”
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Ruzurgi® prescribing information, accessed from DailyMed 9/10/2019
(https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=2731310a-
c060-4d3e-ba41-763d791f63a9)

8. M A K I N G T H E C O M P L E X S E A M L E S S
LEVERAGING PHYSIOLOGICALLY-BASED
PHARMACOKINETIC MODELING (PBPK) MODELING
• Qualitative estimations
• Quantitative estimations
‒ Rare diseases
‒ Oncology
‒ Patient subpopulations (special populations and those with genetic variants)
• Renal impairment
• Pregnancy
• Pediatrics
• Poor metabolizers
‒ Predict the impact of altering dosing regimens
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9. M A K I N G T H E C O M P L E X S E A M L E S S
In Vitro Metabolism and Transporter-Mediated Drug-Drug Interaction
Studies. Guidance for Industry (Draft Guidance), October 2017.
https://www.fda.gov/media/108130/download
Need to understand clinical
exposure in relationship to in
vitro inhibition/induction data
Physiologically- Based
Pharmacokinetic
Modeling Flow Chart
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10. M A K I N G T H E C O M P L E X S E A M L E S S
EXAMPLE: UTILIZING QUANTITATIVE PBPK
PREDICTIONS IN PRODUCT LABELING
INREBIC® (fedratinib) indicated for the treatment of adult patients with
intermediate-2 or high-risk primary or secondary (post-polycythemia vera or
post-essential thrombocythemia) myelofibrosis (approved August 2019)
“Effect of Strong and Moderate CYP3A4 Inhibitors: Coadministration of
ketoconazole (strong CYP3A4 inhibitor: 200 mg twice daily) with a single
dose of INREBIC (300 mg) increased fedratinib AUCinf by 3-fold…Based on
modeling and simulation, coadministration of a strong CYP3A4 inhibitor such
as ketoconazole (400 mg once daily) with INREBIC 400 mg once daily is
predicted to increase fedratinib AUC at steady state by 2-fold…Based on
modeling and simulation, coadministration of moderate CYP3A4 inhibitors,
erythromycin (500 mg three times daily) or diltiazem (120 mg twice daily),
with INREBIC 400 mg once daily is predicted to increase fedratinib AUC at
steady state by 1.2-, and 1.1-fold, respectively.”
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Inrebic® prescribing information, accessed from DailyMed 9/18/2019
(https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f0f55a2a-
4e0c-4cba-8571-03e1424486d7)

11. M A K I N G T H E C O M P L E X S E A M L E S S
WHEN SHOULD DDI INVESTIGATION START?
MHLW: “Information on the investigational drug’s … drug metabolism should
normally be clarified from in vitro studies before starting phase I studies.”*…
“if the major elimination pathway of an investigational drug is metabolism,
drug metabolizing enzymes contributing highly should be identified and the
degree of contribution should be clarified as much as possible”*
EMA: “In vitro metabolism studies should generally be performed before
starting phase I to identify the main metabolites former in vitro…
In vitro studies should also be performed to identify candidate enzymes
responsible for the main metabolic pathways of the parent drug”
FDA: “Sponsors should evaluate DDIs before the product is administered to
patients who are likely to take concomitant medications that could interact
with the investigational drug. Furthermore, sponsors should collect enough
DDI information to prevent patients from being unnecessarily excluded from
any clinical study because of their concomitant medication use.”
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*transcript provided by Cortellis

12. M A K I N G T H E C O M P L E X S E A M L E S S
WHICH SPECIES?
EMA: “Pharmacokinetic interaction studies should generally be
performed in humans. Preclinical studies in animals may sometimes be
relevant, but due to marked species differences, direct extrapolation of
such results to humans is difficult…therefore…in vivo…means in
humans…in vitro studies should be performed using human enzymes
and transporters”
MHLW: “quantitatively evaluate the effect of the precipitant drug on the
object drug’s main elimination pathways…This is achieved by first
conducting in vitro studies using human tissues and drug-metabolizing
enzymes”
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13. M A K I N G T H E C O M P L E X S E A M L E S S
WHEN CAN IN VITRO DATA BE UTILIZED IN LIEU OF A
CLINICAL STUDY?
• Robust in vitro data conducted utilizing human tissue
‒ Qualitative
‒ Quantitative
• Good understanding of the relevant clinical PK of investigational drug
including worst case scenario
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14. M A K I N G T H E C O M P L E X S E A M L E S S
GENERAL DESIGN PRINCIPLES FOR CLINICAL
DDI STUDIES
• Evaluating an investigational drug as a potential substrate (victim)
‒ Need a dosage within the linear PK range (highest dosage in this range not
required)
‒ Potentially can utilize a single dose
‒ Study a strong probe inhibitor/inducer first (if available)
• Evaluating an investigational drug as a precipitant (causative drug)
‒ Highest clinical dosage level
‒ Dose to steady-state of parent
‒ More extended dosing when:
• Metabolites contribute to DDI
• Precipitant demonstrates time-dependent
• Investigating the potential for induction
‒ Exception: when potential perpetrator is indicated for single dose
‒ Time co-administration to maximize possibility of interaction
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May need to evaluate recovery to
baseline enzyme activity

15. M A K I N G T H E C O M P L E X S E A M L E S S
WHAT DO REGULATORY AUTHORITIES SPECIFY
REGARDING DOSAGE AND DURATION?
MHLW – “The dosage of inhibitor or inducer used in the study should maximize the
possibility of drug interactions, and the planned or approved maximum dose and minimum
dosing intervals should be used…
Any dose of substrate can be used, provided that it is within a linear range. The substrate
dose should be fixed with reference to the clinical dose if the substrate pharmacokinetics
shows non-linearity. If there are safety concerns , the substrate dose should be set lower
than the clinical dose, and the influence of variations in dosage on evaluation of drug
interactions should be examined in terms of the detection sensitivity of the analytical
method…
Clinical drug interaction studies should ideally investigate interactions in steady state after
repeat administration of the investigational drug…the investigational drug can be
investigated under single administration if the drug is a precipitant drug with no potential for
time-dependent inhibition or induction. In general, object drugs can be investigated under
single-dose drug interaction studies. If the interaction could cause clinically problematic long-
term variation in the activity of the drug-metabolizing enzyme due to TDI or induction,
evaluation of recoverability after discontinuation of the precipitant drug is recommended
using a crossover study that includes a period in which the object drug is administered alone
after the co-administration period.”
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16. M A K I N G T H E C O M P L E X S E A M L E S S
WHICH METABOLIC ENZYMES SHOULD BE EVALUATED?
• Trend shifting away from CYP3A4 and metabolism in general
• May need to focus on non-P450 enzymes, especially Phase II
• Investigational Drug as a Victim of Metabolic DDIs
‒ Elimination pathways ≥ 25% especially of pharmacodynamically active
metabolites
• Investigational Drug as a Causative Agent of Metabolic DDIs
‒ Consider mechanism-based DDIs (time-dependent), not just competitive
inhibition
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17. M A K I N G T H E C O M P L E X S E A M L E S S
WHICH TRANSPORTERS SHOULD BE EVALUATED?
For metabolically stable drugs with poor permeability: role of transports
is paramount
(-) Few index (probe) drugs – redundancy for both substrates and
inhibitors (ex. OATP1B1 & OATP1B3)
(-) Complex metabolic-transporter interplay
‒ Extended Clearance Classification System
(-) Systemic (plasma) concentrations may not reflect the intracellular
concentrations at the site of action
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18. M A K I N G T H E C O M P L E X S E A M L E S S
WHICH ENZYMES AND TRANSPORTERS SHOULD
BE EVALUATED?
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CYP1A2 CYP2C9 CYP3A4/5
CYP2B6 CYP2C19
CYP2C8 CYP2D6
Consider other enzymes including CYP2A6, CYP2J2, CYP4F2, CYP2E1 and other Phase 1 enzymes
(FMO, MAO, aldehyde dehydrogenase). Also consider Phase II enzymes (UGTs, sulfotransferases).
BCRP OAT1 OATP1B1
MATE1 OAT3 OATP1B3
Mate 2-K OCT2 P-gp
List of Transporters
List of CYP Enzymes
OCT1

19. M A K I N G T H E C O M P L E X S E A M L E S S
Geneva cocktail
caffeine (CYP1A2)
bupropion (CYP2B6)
flurbiprofen (CYP2C9)
omeprazole (CYP2C19)
dextromethorphan (CYP2D6)
midazolam (CYP3A4/5)
fexofenadine (P-gp)
Basel cocktail
caffeine (CYP1A2)
efavirenz (CYP2B6)
losartan (CYP2C9)
omeprazole (CYP2C19)
metoprolol (CYP2D6)
midazolam (CYP3A4/5)
Inje cocktail
caffeine (CYP1A2)
losartan (CYP2C9)
omeprazole (CYP2C19)
dextromethorphan (CYP2D6)
midazolam (CYP3A4/5)
Cooperstown 5 + 1
caffeine (CYP1A2)
warfarin (CYP2C9)
omeprazole (CYP2C19)
dextromethorphan (CYP2D6)
midazolam (CYP3A4.5
+ Vitamin K
COCKTAIL STUDIES
Concurrent administration of multiple probe substrates to evaluate the inhibition potential for
multiple metabolic enzymes and transporters simultaneously
(+) Improved efficiency – may reduce the number of clinical DDI trials
(+) May be particularly useful to minimize confounding due to pharmacokinetic variability
over time (such as with therapeutic proteins and inflammatory disease states)
(-) Probe substrates should not interact with each other (including pharmacodynamic
interactions
Typically utilize an already validated combination of probe substrates
May stagger doses if there is a potential for pharmacodynamic interactions
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20. M A K I N G T H E C O M P L E X S E A M L E S S
SMALL DOSE (MICRODOSING*) DDI STUDIES
• Study design to minimize potential safety issues for participants
‒ Pediatric populations
‒ Targeted oncology agents
‒ May be better suited for healthy volunteer studies (not be appropriate for
patient populations where drug resistance may develop such as anti-infectives)
• Considerations:
‒ Does my drug exhibit linear PK?
‒ Will not predict the pharmacokinetic behavior at therapeutic dosing IF the drug
exhibits nonlinear PK
‒ Need a sensitive analytical assay
• *Microdose 1% of the pharmacologically active dose
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21. M A K I N G T H E C O M P L E X S E A M L E S S
WHICH CYP3A4 INHIBITOR?
Ketoconazole was a strong and relatively selective CYP3A4 inhibitor -
Removed from market in 2013 for safety reasons (hepatotoxicity)
(-) Majority of remaining CYP3A4 inhibitors also inhibit P-glycoprotein
(-) Some are time-dependent inhibitors
(-) Some produce metabolites that are also CYP3A4 inhibitors
Current recommendation: Itraconazole as a strong probe inhibitor
(+) Competitive inhibitor (reversible)
(-) P-glycoprotein inhibitor
(-) Metabolites significantly contribute to CYP3A4 inhibition
(-) Very lipophilic (poorly water soluble) with nonlinear PK (accumulates during
multiple dosing)
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22. M A K I N G T H E C O M P L E X S E A M L E S S
WHICH P-GLYCOPROTEIN SUBSTRATE?
• Permeability glycoprotein (P-gp, MDR1) ATP dependent efflux transporter active in
the intestine and liver. Also functions as a protective mechanism to exclude
compounds at the blood-brain and blood-testes barriers (and tumors)
• Historically both in vitro and clinical DDI studies have utilized digoxin as a probe
substrate
• Digoxin is a narrow therapeutic margin drug that was at one time widely
prescribed to patients with cardiovascular disease. BUT there is increasing
evidence that the digoxin benefit/risk ratio is only positive for a few cardiac
patients with refractory heart rate control
• Data suggests digoxin is neither a specific or sensitive P-gp probe drug
‒ Large interlaboratory variability in vitro
• Fexofenadine, less potential for toxicity but less sensitive/specific
• Dabigatran etexilate, useful for evaluating intestinal P-gp interactions
• No regulatory or consortium consensus
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23. M A K I N G T H E C O M P L E X S E A M L E S S
Recommendations
Total duration of itraconazole: 14 days
Need run-in period of 3 days to reach steady-state inhibition prior to substrate administration
Need to cover 4 – 5 half-lives after substrate administration
Consider loading dose of 200 mg BID or 400 mg QD on Day 1 if substrate has a long half-life
Dose-staggering has no significant impact
UTILIZING PBPK TO OPTIMIZE CLINICAL DDI DESIGN:
ITRACONAZOLE
International Consortium for Innovation and Quality in Pharmaceutical Development working
group developed a verified PBPK model to provide recommendations for optimal DDI study
design.
Collated clinical inhibition data for itraconazole and its metabolites including concentration-
time profiles for these metabolites. Generated new in vitro data.
Evaluated several PBPK models to determine optimal model then utilized “best fit” PBPK
model to simulate clinical trials with multiple CYP3A4 substrates and compared to clinical PK
data from DDI studies
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Liu L, Bello A, Dresser MJ, Heald D, Komjathy SF, O’Mara E, Rogge M, Stoch SA, Robertson SM. Best practices for the use of itraconazole as a replacement for ketoconazole in drug-drug interaction
studies. J Clin Pharmacol Ther. 2014;95:143-51
Chen Y et al. Recommendations for the design of clinical drug-drug interaction studies with itraconazole using a mechanistic PBPK model. CPT Pharmacometrics Syst Pharmacol 2019

24. M A K I N G T H E C O M P L E X S E A M L E S S
OPTIMIZING RIFAMPIN CLINICAL INDUCTION STUDIES
EMA : “to evaluate the full induction effect on a CYP3A4 substrate, a duration of 10-
14 days is recommended for a perpetrator that does not accumulate during multiple-
dose conditions. It is anticipated that this is one of the issues to be addressed in the
new guidance when released” (Concept Paper on a revision of the Guideline on the
investigation of drug interactions, March 2017)
Rifampin: Strong inducer of enzymes regulated by PXR including CYP3A4/5 and
CYP2C19 but induces other enzymes and transporters including CYP1A2, UGTs
and P-gp. Potent inhibitor of OATP1B. Highly variable response to induction among
sensitive substrates but rifampin PK is highly variable and nonlinear (exhibits both
saturable first-pass metabolism & autoinduction).
Recommendation for dose-staggering for substrates of substrates of inducible
enzymes and OATP1B1
The Induction Working Group and researchers from Flinders/Pfizer. Later group
suggested >10 days of rifampin dosing.
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https://www.ema.europa.eu/en/documents/scientific-guideline/concept-paper-revision-guideline-investigation-drug-interactions_en.pdf
Kapetas AJ, Sorich MJ, Rodrigues AD, Rowland A. Guidance for rifampin and midazolam dosing protocols to study intestinal and hepatic cytochrome P450(CYP) 3A4 induction and de-induction. AAPS 2019;21:78
Ramsden D, Fung C, Hariparsad N, Kenny JR, Mohutsky M, Parrott NJ, Robertson S, Tweedie DJ. Perspectives from the IQ induction working group on factors impacting clinical DDI due to induction: focus on CYP3A
substrates. Drug Metab Dispos published ahead of print

25. M A K I N G T H E C O M P L E X S E A M L E S S
HIGHLIGHTS
• Start DDI program early
‒ Preliminary in vitro disposition prior to Phase I
‒ DDI assessments completed prior to administration with concomitant
medications
• Carefully assess DDI program for opportunities to streamline clinical
development program
• Leverage modeling techniques
‒ Optimization of study design
• Selection of dose and dosing interval
• Consideration of concomitant medications
‒ Prediction of worst case scenario
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26. QUESTIONS
THANK YOU