This document discusses microdosing studies, which involve administering very small, sub-therapeutic doses of drug candidates to humans early in clinical trials. The goals are to obtain human pharmacokinetic and metabolic data prior to traditional Phase 1 trials in order to select promising candidates and eliminate unsuccessful ones earlier. Microdosing studies have advantages like accelerating development timelines and reducing costs by focusing resources on candidates more likely to succeed in later trials. The document covers the concept, goals, procedures, uses, advantages, and regulatory guidelines of microdosing studies.

1. Studies
Microdosing

2. Dr. Ashutosh Tiwari
PG Resident (IInd Year)
Pharmacology
SAIMS
04/09/2014

3. PRESENTATION LAYOUT
• Introduction
• Concept of microdosing
• Basic features & Goals
• Regulatory guidelines
• Procedure & Analytical methods
• Uses of Microdosing
• Advantages & Limitations
• Indian scenario
• Challenges
• Conclusion

4. INTRODUCTION
• Drug development is a long, complex and expensive activity.
• requires 10-15 years of sustained efforts, and a cost of US $ 500 million
to $1 billion for a single marketed drug
• Surveys over the past 10 years have shown that whereas R & D
expenditure is increasing almost exponentially year on year, the number
of new molecular entities being registered for marketing is either static or
declining
• The situation has become so serious that the FDA published the
document ‘critical path’, highlighting the problems in drug development
and encouraging novel approaches to be incorporated into the current
drug development paradigm
• The European Medicines Agency (EMEA), published a position paper on
the non-clinical safety studies needed to support human clinical trials
with a single dose of a pharmacologically active compound using the
microdose technique

5. INTRODUCTION

6. INTRODUCTION
• Nearly one-third of the investigational new drugs (INDs) fail in the phase-
1 trials, many due to PK / PD, safety or efficacy issues
• Too low concentrations of drug at the target organ for lesser time can
lead to efficacy failures,
• Wrong concentrations reaching wrong targets for longer time may lead to
toxicity.
• Toxicity failures in animals may be through metabolic routes or pathways
that do not occur in humans.
• Horrobin questioned the value of animals in drug development, stating
that too much focus was being placed on animal models that may not
mirror what happens in humans
• Horrobin DF. Modern biomedical research: an internally self- consistent universe with little
contact with medical reality? Nature Rev Drug Discovery 2003; 2: 151–4.

7. INTRODUCTION
• The latest estimate from the Tufts Center for the Study of
Drug Development is that it costs up to $15 million and
takes 18 months to get a molecule through Phase I.
• If the development programme were to be terminated at this
stage, then the human volunteers would have been un-necessarily
exposed to a failed drug and large numbers of
animals would have been used
• Thus, a new experimental approach has been developed,
known as Phase 0 or microdosing studies, to address
issues pertaining to drug metabolism and
pharmacokinetics.
• It offers a way of developing drugs in a faster, more cost-effective
and ethical way than ever before

8. THE CONCEPT
• The principle of human microdosing is that of safely
administering sub-pharmacological amounts (microdoses)
of NCEs and NMEs to humans to gain valuable
information on human pharmacokinetics,
pharmacodynamics & metabolism at a much earlier stage
• Central to this approach is the concept that –
“the best model for man is man”

9. THE CONCEPT
• Since such low doses are unlikely to have any
pharmacodynamic effects and would be too small to cause any
major side effects after a single dose, it should be possible to
undertake such studies in humans without having to complete
the whole range of classical toxicology studies at therapeutically
effective doses that are mandated prior to regular Phase 1 trials.
• By using only a very tiny amount of active substance, one can
establish the likely pharmacological dose and thereby determine
the first dose for the subsequent Phase I study.

10. What is a Phase 0 trial?

11. PHASE 0 / MICRODOSING STUDTY
• Because human microdosing studies are performed prior to
Phase I, they have come to known as Phase 0 studies
• (although the regulatory authorities never adopted the
terminology and prefer to call them exploratory clinical trials)
• Whilst other methods of pharmacokinetic prediction rely on
extrapolation of data from in vitro, in silico or animal models,
micro- dosing obtains data directly from the target species - that
is human.

12. PHASE 0 / MICRODOSING STUDTY
• In a human microdose study a sub-pharmacologically active
dose of drug is administered and samples (typically plasma) are
collected and analysed for parent drug or metabolites.
• Since the very small doses administered are of low toxicological
risk, regulatory agencies allow a microdose to be administered
to human subjects based upon a reduced safety package
compared to that required for a full Phase I clinical trial
• (that is with no genotoxicology investigations and a single- dose
rodent toxicology study).

13. BASIC FEATURES OF PHASE 0 TRIALS
• First-in-human trial conducted prior to traditional
Phase 1 study
• Small number of subjects (≈10-15)
• Limited drug exposure
• Low, non-toxic doses
• Short duration (≈ ≤7 days)
• One course only
• No therapeutic intent (clinical benefit)
• Phase 0 trials are not definitive studies (further
studies are required)

14. VARIOUS GOALS OF PHASE 0 TRIAL
14
• Provide human PK-PD relationship data prior to
definitive Phase 1 testing
• Evaluate human PK (e.g., bioavailability) to select
most promising candidate for further development
• Eliminating “bad” agents early in clinical development
because of poor PD or PK properties
• e.g., lack of target effect, poor bioavail., very rapid clearance
“Fail fast, fail early”

15. Conventional vs Microdosing study
Extrapolation from animal or in vitro to human via
often complex mathematical models
Traditional models
human to human directly reflecting PK
Microdose

16. CONVENTIONAL VS MICRODOSING STUDY
Variable Phase 1 Trial Phase 0 Trial
Preclinical
toxicology study
Full IND-directed
Less required;
sufficient to support
ExpIND
Regulatory
requirements
established firmly very few & limited
Primary objective &
dose-escalation
scheme
Establish dose-limiting
toxicities and MTD
(maximal tolerable dose)
Establish a dose-range
that modulates
target, for use in
subsequent Phase 1
trials

17. MICRODOSING VS CONVENTIONAL STUDY
Variable Phase 1 Trial Phase 0 Trial
Duration of dosing
Repetitive; multiple
cycles until disease
progression or
unacceptable toxicity
Limited dosing (e.g.,
1-7 days); one cycle
only
Evaluation for
therapeutic benefit
Yes No
PK/PD analysis
Samples usually
batched and analyzed at
a later time point,
generally after
completion of the trial
Performed in “real-time”

18. MICRODOSING VS CONVENTIONAL STUDY
Variable Phase 1 Trial Phase 0 Trial
Special
requirements
None
Radiolabelled
compound
Amount of drug
required
about 100 gm less than 100 μg
Time from
preclinical to first in
human studies
12-18 months 6-8 months
Cost of early phase
drug development
US$ 1.5-5 million US $ 0.3-0.5 million

19. THE ETHICAL DIMENSION
• Central to the whole debate about human microdosing is the
question of ethics
• Is it right to expose healthy volunteers to an NCE at the
Phase I stage with only animal and in vitro data to support
the dose administered?
• If we have the ability to reduce the failure rate of drug
candidates at Phase I for PK / PD reasons, shouldn’t we be
doing it?
• Conversely, how many perfectly good ‘druggable’ candidates
have been thrown out due to inappropriate animal results
which may have been ‘saved’ by human microdosing?

20. HISTORY
• The concept of microdosing first appeared in the late 1990s as a
method of assessing human pharmacokinetics prior to full
Phase I clinical trials and the first data appeared in the literature
in 2003
• Garner RC. Accelerator mass spectrometry in
pharmaceutical research and development-a new
ultrasensitive analytical method for isotope measurement.
Curr Drug Metab 2000;1(2):205-13
• Lappin G, Garner RC. Big physics, small doses: the use of
AMS and PET in human microdosing of development drugs.
Nat Rev Drug Discov 2003;2(3):233-40

21. MICRODOSING & REGULATORY GUIDELINES
• Position paper from the European Medicines Agency in 2004
• EMEA Position Paper on Non-clinical Safety Studies to Support
Clinical Trials with a Single Microdose. CPMP/SWP/ 23. 2599;
2004
• Guidelines from the FDA in 2006
• Food and Drug Administration US Department of Health and
Human Services Guidance for Industry Investigators and
Reviewers. Exploratory 24. IND Studies (January 2006)
• Guidelines from The Ministry of Health, Labor and Welfare, Japan in
2008
• ICH international guideline in 2009
• ICH Topic M3 Note for Guidance on non-clinical safety
pharmacology studies for human pharmaceuticals CPMP/ICH/
286/95; 2009

22. MICRODOSING & REGULATORY GUIDELINES
• There are similarities and differences in the regulations governing
microdosing currently in place in the European Union and in the United
States.
• While both guidances define a microdose in a similar manner, the US
FDA guidance, published later, permits repeated doses for up to 7 days.
• Both require one toxicology study in a single mammalian species at
multiple dose levels, with the highest dose inducing minimal toxic effects.
• But the EMEA guidance requires the use of the IV route in addition to the
intended route of administration, a separate genotoxicity study, and a
1000x safety margin if no toxic effects are elicited with the highest doses,
while the FDA guidance requires only one route of administration and a
100x safety margin.
• Overall, the US regulation is more flexible, allowing more innovative use
of the microdosing tool.

23. MICRODOSING & REGULATORY GUIDELINES
Microdosing Definition –
• A microdose is defined in all of these regulatory documents as being a dose
of drug that is 1% (1/100th )of the pharmacologically active dose determined
from animal models and in vitro systems, up to a maximum of 100 μg.
• The microdose of drug defined by the USFDA is analogous to that defined by
EMEA. In addition, it states an upper dose limit of 30 nanomol for protein
products.
• The latest ICH M3 guideline, now universally accepted, allows a microdose
to be administered to human subjects based on a single-dose toxicity study
(usually in the rat), followed by 14 days observation, using the intended route
of administration (or via the intravenous route), plus some in vitro target
receptor data.

24. MICRODOSING PROCEDURE
• a minimal toxicology package is
required prior to a microdose study
and hence only laboratory-scale
quantities of drug substance are
required
• A microdose is typically administered
to four to six healthy male subjects
(although female subjects have been
used)
• followed by the collection of plasma
and sometimes excreta or biopsy
samples over time
• The samples are analysed for target
analytes such as parent drug or
metabolites to ascertain the
pharmacokinetic profile.

25. ANALYTICAL METHODS
• The low dose administered in a human microdose study will lead to
low plasma-drug concentrations
• therefore sensitive analytical technologies are necessary in order to
make the requisite measurements over an appropriate time.
• Microdosing is dependent on the availability of ultrasensitive analytical
methods able to measure drug and metabolite concentrations in the
low picogram to femotgram range.
• These include accelerator mass spectrometry (AMS) and positron
emission tomography (PET)
• Both these techniques rely on the assessment and analysis of the
radio isotopes incorporated into the drug under study.

26. ANALYTICAL METHODS
• In the case of AMS, [14C] is the most useful isotope for drug
metabolism studies whereas for PET [11C] is proving to be the
most useful.
• AMS is used for determining PK data by taking body samples
over time, processing the samples in the laboratory and then
analysing their drug content.
• PET provides primarily PD data through real-time imaging and
some limited PK data.

27. FLOW DIAGRAM OF MICRODOSE PROCEDURES

28. EXPLORATORY PHARMACOKINETIC DATA
• There are 44 drugs where the data are in the peered reviewed
literature comparing microdose PK to therapeutic dose PK data:
• Oral (34) and IV (11) routes of administration
• Of the oral drugs, 82% were scalable
• Of the IV drugs, 100% were scalable
• Reasons for non-linearity with oral dose
• Target mediated disposition
• Saturability of enzyme and transporter systems
• In order for pharmacokinetic prediction to improve, it is important to
understand the underlying mechanisms responsible for non-linearity
with oral dose

29. EXPLORATORY PHARMACOKINETIC DATA
• Target mediated disposition
• plasma concentrations decrease rapidly as the drug attaches to its
binding site
• At higher doses, as the binding site becomes saturated, then the
plasma concentrations are proportionally higher and the rapid
decrease in concentration at the early time points is no longer
observed
• seen with warfarin, monoclonal antibodies
• Saturability of enzyme and transporter systems
• seen in case of Propafenone, where bioavailability increases
disproportionally to dose, as CYP2D6 become saturated as the
dose increases, thereby reducing the effect of first -pass
metabolism

30. PRINCIPAL PUBLISHED HUMAN MICRODOSE TRIALS
• CREAM (Consortium for Resourcing and Evaluating AMS Microdosing)
• Lappin et al (2006) Clin Pharmacol Ther 80, 203-215
• EUMAPP (European Union Microdose AMS Partnership Programme)
• Lappin, et al (2010) Eur J Pharm Sci 40, 125–131
• Lappin et al (2011) Eur J Pharm Sci 43, 141-150
• NEDO (New Energy and Industrial Technology Development Organization)
Microdosing project, Japan
• Yamane et al 2009 Drug Metab Pharmacokinet 2009; 24(4): 389-
403.
• Tozuka et al 2010, Clin Pharmacol Ther 2010; 88(6): 824-30.
• Yamazaki et al (2010), J Clin Pharm Ther 2010; 35(2): 169-75.

31. EMERGING USES OF MICRODOSING
• Although the emphasis has been on pharmacokinetic prediction,
there are other applications of microdosing that are emerging
• Microdosing has also been applied to the study of
• drug-drug interactions
• measuring drug concentrations at the site of action
• metabolic profiling
• study in vulnerable populations

32. EMERGING USES OF MICRODOSING
• Drug-drug interactions:
• The pharmacokinetics of a development drug administered as
a microdose before and after administration of
pharmacological active doses of a suitable inducer or inhibitor
of a chosen enzyme or transporter is compared.
• Measuring drug concentrations at the site of action
• A drug that exhibits an appropriate concentration at its site of
action for a required period of time, but is also present off -
target (e.g., in the plasma) to only a limited extent, will stand
the best chance of having the necessary balance between
high efficacy and low toxicity

33. EMERGING USES OF MICRODOSING
• Metabolic profiling
• To obtain preliminary data on the metabolism of a candidate, drug
samples from microdose studies have been metabolically profiled.
• Study in Vulnerable populations
• The inherent toxicological low risk of a microdose allows
pharmacokinetic studies to be performed in vulnerable populations
(children, pregnant women, elderly, hepatically and renally
impaired), who are routinely excluded from clinical trials due to
safety concerns.

34. MICRODOSING STUDIES: ADVANTAGES
• help in the early selection of promising compounds for further
development before the traditional phase-1 trials
• help in overall acceleration in the process of drug development by
focusing only on the promising compounds
• avoid unnecessary exposure of the participants in the trial to the
not so promising compounds
• the not so promising molecules can be eliminated earlier, thereby
saving costs

35. MICRODOSING STUDIES: ADVANTAGES
• pose less risk of human toxicity owing to the low dose of the test substance,
less duration of administration/ exposure to the drug and very limited number of
subjects involved
• such trials mostly involve a single dose administration as compared to a dose
escalation study in the traditional phase-1 trials, thereby further minimizing the
risk
• lesser pre- clinical safety package is required as compared to the traditional
phase-1 studies
• less number of animals is used
• small quantity of the test drug is required; the test drug may be prepared as per
the principles of the Good Laboratory Practices (GLP) unlike Good
Manufacturing Practices (GMP) compliance as required for the traditional
phase-1 studies

36. MICRODOSING STUDIES: ADVANTAGES
• the drug can be tested in the sensitive population like patients with
renal impairment, women in their reproductive age, cancer
patients, etc,
• helpful in establishing the likely pharmacological dose and thereby
determining the first dose for the subsequent phase-1 study
• the PK data for initial dose selection can be obtained in nearly six
months as compared to nearly 18 months in case of conventional
phase-1 studies
• the overall cost of conducting a microdose study (US$ 0.3 – 0.5
million) is far less as compared to that of a conventional phase-I
study (US$ 1.5 -3 million)

37. MICRODOSING STUDIES: LIMITATIONS
• We still do not have enough studies to clearly exemplify whether the body's
reaction to a particular compound is similar, when used as microdose and in its
pharmacological dose;
• it could lead to false negatives (compound being rejected) or
• false positives (compound acceptable based on microdose data but rejected
subsequently when used in pharmacological doses).
• caution needs to be exercised while applying this methodology to
the drugs showing complex/non-linear kinetics
• since certain drugs dissolve readily at low doses but exhibit limited
solubility at higher doses, it may be difficult to predict the
absorption characteristics at the microdose levels

38. MICRODOSING STUDIES: LIMITATIONS
• there is lack of any therapeutic and/or diagnostic intent
• as there is no therapeutic intent, it may be difficult to motivate
the volunteers to become a part of the trial
• there is requirement of ultra sensitive and high tech equipments
like AMS and PET which are scarcely available
• For both PET and AMS, drugs must be labelled at metabolically
stable sites.
• The database for microdosing studies is very small

39. STATUS IN INDIA: CURRENT STATUS
• In 200708 the Indian Society for Clinical Research (ISCR)
proposed a change in regulation that would allow the regulators to
recognize and permit microdosing studies in India.
• The Drugs Technical Advisory Board unanimously approved the
proposal together with other farreaching amendments in
regulation.
• The proposals were, nevertheless, disregarded by the government
due to nontechnical sensitivities that surround clinical research and
drug development in India.
• Since then, regulatory reform in drug development science has
stagnated.

40. STATUS IN INDIA: FUTURE
• Regulatory change enabling Phase 1 and microdosing studies
would open the door to the science of early clinical development,
setting the stage for rapid growth and scientific advancement in
pharmaceutical development in the country
• this could bring India into the mainstream of pharmaceutical
research and laying the foundation for a possible central role for
the country in global drug development

41. MICRODOSING STUDIES: CHALLENGES
• there seems to be scientific inertia & length of time required to get
new approaches adopted
• failure to recognize the potential benefits of microdose studies
• human microdosing is a promising strategy and despite several
obstacles in terms of infrastructure, existing regulations and ethical
challenges, the issue is worth considering.
• There is a need for scientifically validating microdosing studies in
the field of drug development with an aim of benefiting the
patients, the animals, the pharmaceutical industry and the mankind
as a whole.

42. CONCLUSION
• Human microdosing holds significant promise as an analytical tool.
• Microdosing may help both patients and the pharmaceutical industry with
earlier availability of new test medication and reduced attrition of
compounds at later stages of drug development.
• Microdosing allows not only selection of drug candidates more likely to
be developed successfully, but also helps in determination of the first
dose for the subsequent Phase I clinical studies.
• In the coming years, as research methods and technology involved in
Phase 0 trials become more sophisticated microdosing is likely to
become an accepted approach in drug development so that eventually all
first in human studies will commence with a Phase 0 study.

44. “the difficulty lies not in the new ideas,
but escaping from the old ones”
- John Meynard Keynes