Microdosing: Safer clinical trials and fewer animal tests

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ISSN 1757–6180
Bioanalysis (2010) 2(3), 393 –395
10.4155/BIO.09.168 © 2010 Future Science Ltd
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Human microdosing belongs to the group of
new, advanced experimental approaches that
meet 21st Century requirements. As suggested
by the Centre for Medicines Research, without
a new generation of product-development tools,
it will be difficult to improve the 20-year low in
the number of new medical therapies launched
onto the market [1], despite more investment
in biomedical research worldwide over the last
two decades.
As mentioned in the ‘critical path’ report
published by the US FDA [101], 92% of com-
pounds that pass animal tests fail in Phase I
clinical trials. A technique such as microdosing,
which provides early data about the behavior
of drugs in humans at very low doses, can only
improve predictions of drug toxicity and effi-
cacy, whilst also reducing the resources spent
and the number of animal tests carried out.
In streamlining the drug-development pro-
cess, human microdosing is also likely to reduce
animal testing, a responsibility shared by com-
panies, regulators and individual scientists
worldwide. Legislation in Europe requires the
Replacement, Reduction and Refinement (the
‘Three R s’) of animal experiments wherever
possible [2]. Similar policies are implemented in
many countries, including the USA.
In the EU, the Commission and the member
states also have a legislative duty to encourage
research into methods that could achieve equiva-
lent objectives, but using fewer animals or none
at all. The European Centre for the Validation of
Alternative Methods (ECVAM) was established
in 1992 for this reason and, since then, some 27
nonanimal models and assays have been scien-
tifically validated as full or partial replacements
for animal tests and 20 have gained regulatory
approval [102].
More than 12.1 million animals were used
in 2005 (latest available figures) in experiments
in the EU, of which 528,189 were used for
safety testing of pharmaceuticals [3]. As well as
their use in studies of absorption, distribution,
metabolism and excretion (ADME), animals are
used to assess longer-term toxicities of pharma-
ceuticals, such as subchronic and chronic toxic-
ity (67,651 animals in the EU in 2005), devel-
opmental and reproductive toxicity (49,026
animals) and carcinogenicity (26,589). The
wider use of human microdosing would mini-
mize all these animal tests, which are conducted
later in drug development, by providing human-
specific ADME data and, thus, identifying early
those compounds destined to fail later owing to
suboptimal pharmacokinetics or metabolism [4] .
A 10% improvement in identifying failing can-
didates before classic clinical trials could also
save US$100 million in development costs per
drug [5].
The British government’s Animal Procedures
Committee, which advises on animal experi-
ments, recommended in its 2002 report on
the use of primates that human microdosing
should be further developed and resourced. The
Committee recognised that microdosing has the
potential to limit the use of primates in repeat-
dose toxicity tests, pharmacokinetics and safety
pharmacology studies [6]. In 2008, repeat-dose
tests alone (subacute, subchronic and chronic)
involved 2346 primates in Britain [7].
In contrast to the fairly extensive animal
data required prior to a Phase I trial, single-
dose rodent tests can be the primary support
for microdose studies in humans and the
European Medicines Agency recognizes that
micro dosing, among other kinds of exploratory
clinical trials “can reduce overall animal use in
drug development” [103].
The use of subpharmacological and sub-
therapeutic microdoses in early clinical stud-
ies also offers better protection for Phase I trial
volunteers, without compromising the safety of
microdose subjects. It has been suggested that a
microdose study of TGN1412 might have pre-
vented the tragedy that occurred in 2006, when
Phase I trial subjects suffered life-threatening,
unexpected side effects despite extensive pre-
clinical tests on animals, including rhesus and
cynomolgus monkeys.
“The wider use of human microdosing would minimize all these animal tests … by providing human-specic ADME data and,
thus, identifying early those compounds destined to fail later owing to suboptimal pharmacokinetics or metabolism.”
Microdosing: safer clinical trials and fewer
animal tests
Gill Langley
Author for correspondence
Dr Hadwen Trust for
Humane Research, 18 Market
Place, Hitchin, Herts,
SG5 1DS, UK
Tel.: +44 1462 436 819
Fax: +44 1462 436 844
E-mail: sciencesources@
btinternet.com
Sebastien Farnaud
Dr Hadwen Trust for
Humane Research, 18 Market
Place, Hitchin, Herts,
SG5 1DS, UK
Tel.: +44 1462 436 819
Fax: +44 1462 436 844
E-mail: sebastien@
drhadwentrust.org

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news & AnAlysis | OpiniOn
TGN1412 targets the CD28 receptor on
T-cells, where there are differences between
the rhesus monkey and human sequences. A
microdose study with TGN1412, by systemic or
dermal application, could have determined the
amount of the antibody that bound to T cells
in the whole human body without risk to the
subjects, as well as providing pharmacokinetic
and metabolic data relevant to the human spe-
cies [8]. Safely obtained human microdose data
may have been able to improve the design of the
Phase I study.
In fact, the Duff report on the TGN1412 inci-
dent stated that “the view that higher-risk agents
should be given at specified low dose levels, for
example in the microgram or nanogram range
(‘microdosing’ and ‘nanodosing’) may have
value as a general guideline” [104].
The human relevance of microdosing applies
to a wider field than drug toxicology, as illus-
trated by its proposed uses in oncology. For
example, applying microdosing to measure
interindividual variability in drug disposition
caused by genetic and environmental factors is a
promising application [9]. In addition, microdos-
ing offers opportunities to conduct new study
designs and investigate previously unanswerable
questions in oncology [10].
The value of microdosing in other sectors
has already been recognized. As a case in point,
microdosing was considered by an ECVAM
expert group as a potential replacement for most
of the toxicokinetic and ADME data normally
obtained from animal tests for chemicals used
in cosmetics [11] .
The role of nonanimal techniques
Many researchers, governments and regula-
tors now agree that replacement techniques are
often more relevant, reliable, sensitive, cost-
effective and reproducible than experiments
on animals [105]. The FDA’s report stated that
a major problem is the failure to create and use
novel tools to deliver “fundamentally better
answers about how the safety and effectiveness
of new products can be demonstrated, in faster
time frames, with more certainty, and at lower
costs” [101].
The FDA called for a greater emphasis on
in vitro, clinical and computational tools. For
example, using human cell lines to character-
ize drug metabolic pathways can predict human
metabolism and help eliminate compounds with
unfavorable metabolic profiles. This approach
has meant that clinical failures due to drug-
interaction problems are now far less likely.
Computational modeling is increasingly being
applied to human disease simulation, to predict
novel drug pharmacokinetics and to conduct ‘vir-
tual’ clinical trials. In terms of ADME simula-
tion, the mathematical relationship between drug
doses, plasma concentrations, pharmacokinetics
and pharmacodynamics can be characterized
and patient covariates are included in the com-
putational model. The systematic application
of mathematical modeling could significantly
improve drug development.
Analytical techniques have already replaced
many animal tests and in so doing have improved
sensitivity, reliability and precision [12]. For exam-
ple, digitalis was once routinely tested for potency
on guinea pigs and pigeons using a lethal method.
In the late 1980s, this was replaced by a chemical
colorimetric assay which directly measured the
content of digitoxin. In 1980, insulin batch test-
ing used 600 mice per test, but was later replaced
by HPLC – a more rapid and precise method [13].
Where now?
The number of consortia and organizations work-
ing to replace animal tests in medicines develop-
ment is growing fast. The European Partnership
to Promote Alternative Approaches to Animal
Testing was established in 2005 as a joint ini-
tiative between the European Commission,
European trade associations from seven indus-
try sectors (including pharma ceuticals) and
individual companies. Its purpose is to promote
the development and implementation of mod-
ern Three R approaches, including non animal
methods, in the field of safety testing [106].
In 2009, an international memorandum of
co-operation was signed by four agencies, in the
USA, Japan, Canada and the EU, to co-ordinate
the adoption of nonanimal testing methods. The
agreement “will speed the adoption of new test
methods based on advances in science and tech-
nology. Animal welfare will also be improved
by the national and international acceptance of
alternative test methods that reduce, refine and
replace the use of animals”, according to William
Stokes, an assistant surgeon general in the US
Public Health Service and a leading scientist in
the Three Rs field [107].
Although nonlinear absorption or disposi-
tion characteristics could affect the validity
of microdose predictions of therapeutic-level
pharmaco kinetics, recent publications suggest
that a concordance of approximately 80% can
be anticipated [14]. Its direct and safe applica-
tions for humans, together with its economical
and ethical benefits, bring microdosing to the
Bioana lysis (2010) 2 (3)

www.fut ure- scie nce.com 395
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forefront of 21st Century technology. Combining
human microdosing with other complementary
non animal approaches clearly offers ethical, sci-
entific and efficiency benefits for pharmaceutical
development. Wider recognition of this should
lead to faster progress towards that goal.
Financial & competing interests disclosure
Both authors are employed by the Dr Hadwen Trust for
Humane Research (Registered Charity No 261096), the
UK’s leading medical research charity exclusively funding
nonanimal research techniques to replace animal experi-
ments, benefiting people and animals. The authors have
no other relevant affiliations or financial involvement
with any organization or entity with a financial interest
in or financial conflict with the subject matter or materi-
als discussed in the manuscript. This includes employ-
ment, consultancies, honora ria, stock ownership or
options, expert t estimony, grants or patents received or
pending, or royalties.
No writing assistance was utilized in the production of
this manuscript.
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