Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5849_Библиотеки_им_академика_М_И_Перельмана
.pdf
degradation of the compound. Any information or observations noted during the
synthesis or purification of the compound may be very valuable for formulating
the compound.
Described below are some typical formulation vehicles that can be used as a
starting point when the information about the newly synthesized compound is limited.
Some strategies for selecting appropriate formulations are described in these
publications [43, 44].
IV Formulations The formulations used for IV administration may vary significantly between labs and researchers. An ideal formulation for IV administration
should contain only water and water-soluble components (salts, buffers). The aqueous
solubility of some compounds can be increased by using an appropriate buffer to make
the molecule more polar by ionizing its functional groups such as amines, heterocycles, acids, and others [43]. The acceptable pH range for IV formulations may vary
from 2 to 12 [44]. The acceptable range of pH for the IV formulation may be expanded
with the use of a lower dosing volume but must be balanced with the in vivo tolerability
requirements [47].
The majority of newly synthesized drug candidates possess low aqueous solubility
and may require the use of acceptable organic cosolvents such as dimethylacetamide
(DMA), propylene glycol (PG), ethanol, or polyethylene glycol 400 (PEG400)
(DMA), N-methyl-2-pyrrolidone (NMP; pharmasolve), dimethylsulfoxide (DMSO),
and others [44] in order to achieve a desired concentration of the compound in the IV
formulation. These solvents are fully miscible with water and aqueous solutions (e.g.,
PBS, phosphate buffered saline). Although the use of undiluted (straight) organic
solvents as the only or the major excipient in the formulations for animal dosing is
documented in the literature, there is a potential impact on the oral bioavailability, the
rate and the mechanism of absorption, and other PK properties of the test compound.
The use of the cosolvents may be combined with pH adjustment. A detailed evaluation
of organic solvents in formulations is described in a series of publications by
Yalkowski et al. [48–53].
The formulation of a compound for IVadministration must be a true solution and
may need to be filtered before administration to animals. Although visual inspection
of the IV formulation for apparent absence of particles may be sufficient in many
cases, there are examples when some insoluble microparticles may cause significantly
erroneous PK profiles.
The requirements for single-dose studies are less stringent than for multiple-dose
studies. In the case of a single-dose IV administration, a higher concentration of
organic cosolvents or other excipients can be used.
PO Formulations Oral administration of animals can be done via oral gavage, oral
administration of capsules, or adding the test compound to animal food or drinking
water (dietary admixtures).
ORAL GAVAGE Oral gavage is the most typical form of administration in discovery
settings. In this case, a solution or a suspension formulation can be used to administer
248 PHARMACOKINETICS FOR MEDICINAL CHEMISTS
https://t.me/medicina_free
the compound directly into the animals stomach via a plastic or a metal gavage needle
attached to a syringe. Usually, oral gavage is followed by some washing step to rinse
the remaining formulation from the syringe and administered to the animals.
SOLUTION FORMULATIONS FOR ORAL GAVAGE A solution formulation of a compound
typically provides the “best case scenario” for achieving the highest possible exposure
and oral bioavailability after PO administration. Compounds in solution do not have
to change from a solid form and are essentially ready for absorption after administration. If the compound is formulated using a relatively high amount of an organic
cosolvent, there is a possibility for the compound to precipitate from the solution
in the stomach after dosing. The formulation may become diluted with gastric fluid
and the reduced conce ntration of the organic cosolvent may not be sufficient to
maintain the compound in solution. The dilution phenomenon should be remembered
when comparing the PK data after administration of poorly soluble compounds in
solution and suspension formulations. If this occurs, the PK profile may show some
animal-to-animal and study-to-study variability depending on the rate of oral gavage,
the fed/fasted state of the animals, and other parameters.
An ideal PO formulation should contain only aqueous buffers, which may be
achieved in certain cases by adjusting the pH of the formulation to ionize certain
functional group of the compound similar to the IV formulation. The range of the
acceptable pHs for oral formulations is typically broader: from 2 to 10 [44].
If pH adjustment is not sufficient to achieve a target concentration of the compound
in the PO formulation, certain water-miscible cosolvents may help solubilize the
compound at a higher concentration in PO formulations. Some of the water-miscible
organics that can be used are polyethylene glycol 400, ethanol, propylene glycol, and
glycerin along with many water-soluble nonionic surfactants [44].
An alternative strategy for PO formulations of highly water-insoluble compounds
may be to use nonwater-miscible organic media such as peanut oil, corn oil, and
others [44].
In addition to using organic cosolvents, an oral solution may be developed using
some pharmaceutically acceptable surfactants such as Cremophor EL, polysorbate 80
(Tween 80), and many others [44]. Althoughsurfactants are widely used even for human
formulations, it is important to consider that some of the surfactants (e.g., Cremophor
EL) may serve as the inhibitor of the intestinal P-gp efflux pumps [54] and increase
oral bioavailability of some drugs like saquinavir in a dose-dependent manner [55].
SUSPENSION FORMULATIONS FOR ORAL GAVAGE Suspension formulations are widely used
for oral administration of newly synthesized compounds in discovery settings to
conduct PK, efficacy, or toxicology studies.
Suspension formulations have several advantages over solution formulations for
oral dosing:
.
Multiple standard or well-established recipes are available in the literature.
.
The compound is less likely to degrade chemically in a suspension formulation
because only the surface of the solid material is in cont act with the solution.
PK PRACTICES 249
https://t.me/medicina_free
.
A suspension formulation may provide more realistic assessment of oral
bioavailability that may be easier to translate to a tablet formulation.
.
In toxicology studies, suspension formulations allow avoidance of organic
cosolvents, surfactants, or other excipients, which may exhibit toxicity by
themselves or exacerbate the toxicity of the test compound causing difficult
interpretation of toxicology results.
At the same time, suspension formulations may have some disadvantages com-
pared to solution formulations for oral gavage:
.
Their PK properties may strongly depend on the particle size and size distribution, which may be difficult to reproduce in discovery settings (especially for
early stage projects when the amount of the material is limited).
.
Their PK properties may strongly depend on the crystalline or amorphous form
of the material and on a polymorphic composition, which may be challenging to
reproduce for discovery compounds.
.
The loss of material in the preparation of a suspension formulation may be much
higher compared to the solution formulation.
.
It may be more challenging to maintain homogeneity of a suspension formulation prior to in-life administration. Some suspensions may tend to sediment
on the bott om or the edges of the formulation vessel, which may lead to
inconsistent filling of the gavage syringe, and as a result, an inconsistent dosing
of the animals.
.
Reproducible administration of suspension formulations may be more challenging even for highly trained animal technicians, which may lead to higher
variability of PK data. Special attention is required to wash the gavage
syringe.
.
Smaller animals such as mice may require a very fine suspension formulation
due to the small gauge of the gavage needle. The needle may clog leading to
inconsistent dosing of animals.
ADMINISTRATION OF CAPSULES Small-sized capsules can be used to administer com-
pound to larger animals such as dogs or monkeys and even rats although this technique
is not frequently used in discovery studies.
DIETARY ADMIXTURES Adding compound to animal food or drinking water may be
a reasonable formulation option for long-term efficacy studies. The advantage of this
formulation is in minimal animal handling (essentially, the compound is selfadministered), which reduces animal stress and the risk of dosing error compared
to oral gavage. However, this type of formulation may provide variable PK profiles in
animals.
Other Formulations The use of formulations other than IVand PO for PK studies in
discovery settings is less common. Less common PK studies typically aim to provide
250 PHARMACOKINETICS FOR MEDICINAL CHEMISTS
https://t.me/medicina_free
data to support animal efficacy and toxicology studies and occasionally FIH dose
projection.
5.6.2.3 Animal Species Used for PK Studies The selection of an animal species
for a discovery PK study may depend on the stage of the project and the purpose of the
PK study. If the study is conducted to compare a new compound with a known
benchmark compound, then the same species and ideally the same strain should be
used for PK assessment. If the PK study is conducted in support o f efficacy studies,
the species and strain selection may be driven by the type of animals used for efficacy
measurement [33]. For the preparation of safety studies, the toxicology species
selection is likely to drive the decision. Unfortunately, there is no single species that
can be used for all the above and additional purposes.
Described below are the animal species and strains most frequently used for PK
discovery studies. These include mice, rats, dogs, and monkeys, and with lesser
frequency guinea pigs, hamsters, and rabbits. Since animals have been used in
pharmaceutical development for decades, a significant amount of literature exists
describing a broad spectrum of applications of animals for discovery and development
purposes [3, 56–58].
Gender Male animal species are used much more frequently than female species
in discovery studies except for the studies in preparation for reproductive
toxicology assessment. In this case, female rats and rabbits are generally the
rodent and nonrodent species for embryo–fetal development studies. It is
important to evaluate PK properties of new drug candidates in both males and
females due to some obvious difference in their hormonal status as well as less
appreciated differences in brain and neurochemical processes, which may be
critical for CNS targeting drugs [59].
There are certain drug-metabolizing enzymes that are gender-specific. For
example, the carbonyl reductase is expressed only in male rats. This enzyme
reduces the carbonyl group of acetohexamide, an oral antidiabetic drug [60].
It is a good scientific practice to match the gender of the animal species used
for PK assessment and respective efficacy studies especially if a particular
gender is more prone to developing a certain disease. Since female nonobese
diabetic (NOD) mice have higher propensity of spontaneously developing
diabetes [61], it is more rational to evaluate drug candidates for the treatment
of diabetes in this gender.
Animal Age The difference in the age of the animals may lead to a noticeable
difference in PK parameters of the compounds. Some PK parameters of
ibuprofen in older Fischer rats were different than in young adults due to
decreases in albumin concentration, the number of albumin-binding sites and
reduction in metabolic activity in aged animals [62].
Genetically Modified Animals Although some genetically modified rat models
are presently available, the mouse is the most widely used genetically modified
animal model for research in integrative biology, toxicology, and pharmacokinetics [63].
PK PRACTICES 251
https://t.me/medicina_free
A significant number of genetically modified mice (GeMMs) have been
developed since the introduction of the techniques in the 1980s and their use in
PK studies is well documented in the literature [64, 65]. Some of the mouse
models allow for the evaluation of the ADME properties. Transporter null mice
may provide information about role of transporters in drug PK [66]. The
chimeric mice with humanized liver can be used for the advanced prediction
of human pharmacokinetics and toxicity [67–70]. In spite of their advantages,
there are limitations of genetically modified mouse models [63].
Rats Rats are frequently used for discovery PK and other studies because of the
significant historical data set that can be used to compare a newly synthesized
compound with its benchmark compounds. There are three main classes of rats used in
research—outbred stocks (e.g., Sprague-Dawley [SD], Wistar), inbred strains (e.g.,
Fischer), and mutants (including transgenic stocks) [71]. The outbred stock animals
contain the maximum amount of genetic differences [72], while the inbred animals
are more genetically homog eneous [73]. Selecting the most appropriate rat strain may
depend on the stage of the project and the purpose of the PK study. For early stage
projects, some standard rat strains are more practical because they are commercially
available on a regular basis in cannulated and noncannulated form, less expensive,
and have a significant amount of historical reference data for other compounds. For
some later stage projects, there may be a need to switch to a different rat strain to
match with the strain used for efficacy or biomarker studies or to prepare PK data for
toxicology evaluations. There is no “ideal” rat strain that fits all the needs of
pharmaceutical discovery. The choice of rat can be complicated, especially when
over 200 different strains of rat are known to exist [71].
The variation of the ADME-related properties between the different strains of rats
is well documented in the literature. They need to be taken into account when
selecting a particular rat strain for specific PK experiments. For example, the activity
of aldehyde oxidase may vary between SD and Wistar rats as well as the different SD
and Wistar substrains [74, 75]. These differences lead to a marked strain differences
in the in vivo metabolism of methotrexate [74]. The difference in the activation of
brain zones in different rat strains may perhaps be important for selecting the most
appropriate model for the drugs targeting CNS [76].
SPRAGUE-DAWLEY SD, an outbred rat strain (CRL strain SAS SD #400, HSD:Sprague
Dawley SD), has been widely used historically in discovery settings. A large amount
of well-documented information about SD rats exists in the literature. SD rats are a
general multipurpose model most frequently implemented for safety and efficacy
testing. SD rats tend to be heavier than WH rats of the same age and gain weight faster
than WH rats. The typical age and weight of male SD rats used for PK studies is in the
range of 10–13 weeks and 300–325 g, respectively.
WISTAR HAN Wistar Han (CRL:WI(Han) strain #273, HSD:RccHan:WIST) is an
outbred multipur pose rat strain. The typical age and weight of male WH rats used for
PK studies is in the range of 10–13 weeks and 300–325 g, respectively.
252 PHARMACOKINETICS FOR MEDICINAL CHEMISTS
https://t.me/medicina_free
OTHER RAT STRAINS Lewis (CRL strain #004) rats are inbred. They are commonly used
in efficacy studies, in particular in induced arthritis/inflammation animal models.
Other commonly used rat strains are Fischer (inbred), Long-Evans (inbred or
outbred), Lister-Hooded (outbred), Brown Norway (inbred), and spontaneously
hypertensive rats (SHR) (inbred).
The differences between rat strains and substrains are important because laboratory animals are bred by different breeders. Despite having a similar name, these
animals may have different genetic and physiological characterizations that can alter
the ADME-related data. For example, Zucker Diabetic Fatty (ZDF) inbred rat (CRL
strain #370) is a mutant version of Zucker rat and listed separately from Zucker obese
rats (CRL strain #185) on the CRL website (www.criver.com).
Mice Mice are frequently used for early stage discovery PK studies aiming to
support efficacy results as well as selection of doses and formulations during efficacy
evaluation. There are three main classes of mice used in research—outbred stocks
(e.g., Swiss-Webster, CF1, ICR (CD-1)), inbred strains (e.g., C57BL, DBA/2, C3H,
and BALB/c), and mutants (including transgenic animals) [73]. Hybrids which
consist of crossing two strains of mice are also available (B6C3F1). Transgenic and
genetically modified models are also available. Choice of strain and type of mouse
used for studies is dependent of study purpose and disease model being considered.
Certain strains of mice may be more susceptible to a certain disease than others. More
information about the mouse strains can be found on the websites of the common US
vendors including Charles River Laboratories (www.criver.com), Harlan (www.
harlan.com), Taconic (www.taconic.com), and Jackson Labs (www.jax.org).
The advantage of using mice for PK is their small weight ranging from 15 to 30 g,
which allows for conducting studies with less amount of compound. Typically,several
mice (frequently N ¼ 3) are sacrificed after dosing at predetermined time points to
collect blood or tissue samples for PK assessment.
The compound savings in mouse PK studies may become less significant if a
mouse study protocol calls for collecting 10 or more time points per administration.
In this case, the amount of the compound may become comparable to or even higher
than a similar rat study (e.g., N ¼ 3 rats per study).
There is a widespread perception that the clearance of the drugs in mice is higher
than in rats [77, 78] and other species. The difference is attributed to the higher
blood flow in the mouse compared to other species such as the clearance becomes very
similar once normalized to a heartbeat rate as shown on Figure 5.27 [79]. There are
examples of drugs whose clearance is very similar in rats and mice such as
ciclesonide [80].
Dogs As a nonrodent species, dogs are often used in safety and/ or pharmacology
testing. Purposely bred, beagle dogs are often the breed of choice ([3], p. 567).
Desirable features in the beagle are its medium size, moderate hair coat, and even
temperament. The body weight of dogs is dependent on the gender and the age of the
animals. An average weight of 15 kg can be safely used for calculation of the amount
of the compound needed for dog studies.
PK PRACTICES 253
https://t.me/medicina_free
Dogs are a United States Department of Agriculture (USDA) regulated species and
animal facilities using dogs are required to follow stringent requirements of the
regulatory authorities [82]. The total number of dogs used for research purposes in the
United States was about 72,000 in 2007, which was an increase from about 67,000
used in 2005 [83].
Dogs used for PK studies are often used for multiple studies following a washout
period, unlike mice or rats that typically are used for a single study. Dogs along with
cynomolgus monkeys are the most commonly used nonrodent species for toxicology
studies. An estimated 140,000 dogs are used worldwide in research and testing every
year primarily in the United States (50%) and Japan [82].
Nonhuman Primates The use of nonhuman primates (NHP) in animal testing for
new drug discovery and development has a long history but also associated with
significant ethical, legal, and scientific challenges and controversy.Although there is a
strong desire to replace NHPs in pharmaceutical animal testing, a significant and
a rising number of primates are used in the United States (around 70,000 in 2007
compare to about 58,000 in 2005) [83].
Monkeys are used in discovery PK studies perhaps least frequently compared to
rodents and dogs. This is because of ethical considerations as well as the cost and
availability of the animals. In some cases, monkeys rather than dogs may be used for
toxicology studies if, for example, monkeys show a metabolic profile more consistent
with that in human. Although there is a widespread perception that monkeys may
predict human PK better than rats or dogs [84, 86], there is no consensus regarding
better translation of monkey PK data to human PK. Some recent analyses showed that
a single animal species scaling to human may produce similarly acceptable results
based on either rat, dog, or monkey data [25].
Figure 5.27 Perceived differences in the half-life of ceftizoxime in various mammals depend
on the references system used to denote time: (a) half-life is reported in minutes, the smaller
mammals eliminate 50% of the drug more rapidly than the larger species. (b) When half-lives
are reported in heartbeats, all mammals eliminate 50% of the drug in the equivalent time.
Adapted from Refs. [79, 81].
254
PHARMACOKINETICS FOR MEDICINAL CHEMISTS
https://t.me/medicina_free
RHESUS AND CYNOMOLGUS MONKEY The rhesus and cynomolgus macaques are the
species of choice for the studies in nonhuman primates [87, 88]. The studies in
monkeys are usually conducted in preparation to toxicology studies in those species
if the dog model is found less predictive of the human safety outcome.
CHIMPANZEES Although the studies in chimpanzee played a crucial role in the
development of the vaccine for hepatitis B [89], the use of chimpanzees for
pharmaceutical research causes much discussion in the scientific community [90–94].
Others Species Other animal species used for discovery PK are rabbits, mini-pigs,
guinea pigs, and hamsters. Rabbit PK studies are usually conducted in preparation for
a reproductive toxicol ogy studies or in some specialized areas such as ophthalmic PK
and efficacy.
Genetically Modified Animals Genetically modified animals, primarily mice, have
become more and more commercially available. Certain genetically modified mice
can provide valuable information about the route of elimination of compound and
can be used for better prediction of human clearance. Humanized mice can be used for
better prediction of human clearance. For example, the elimination of the glucuronides can be studied in the UGT1A1 28/ugt1–/– humanized mice [95]. Some
information about genetically modified animals can be found at http://www.srtp.org.
uk/srtga014.htm.
Animal Physiology in Comparison with Human Physiology Information about
laboratory animal physiology and anatomy can be found in the literature [16, 96].
A summary of selected PK relevant physiological parameters of laboratory animals
and humans can be found in Section 5.8 (Appendices).
5.6.2.4 Animal Dosing There are multiple publications describing most commonly acceptable animal dosing and sample techniques [3, 97].
Potential routes of administration of compounds to the body and potential routes
of biological sample collection for PK evaluation are shown in Figure 5.28. Compounds can be injected into a vein or portal vein representing systemic or presystemic
circulation, respectively. Alternatively, compound can be administered extravascularly (EV), that is, external to the circulation. The most frequently used EV routes
of administration are oral (PO), intraperitoneal (IP), subcutaneous (under the skin),
and intramuscular administrations. There are several routes of administration of
a compound directly into different sections of the digestive tract such as intraduodenal (ID, into the duodenum of the small intestine) or intragastric (IG, into the
stomach).
Additionally, compound can be introduced into the body in a very short period of
time via a so-called bolus administration or it can be infused into the body via an
infusion mechani sm typically by using infusion pumps. Depending on the purpose of
a PK study,it may require using different combinations of routes of administration and
routes for sample collection.
PK PRACTICES 255
https://t.me/medicina_free
If a PK study is conducted to support an efficacy study in an experimental animal
model, then the route of administration is dictated by the efficacy study design. If a PK
study is conduc ted in preparation to a toxicology study, then the route of administration has to be the same as the intended route of administration in FIH study.
The most frequently used methods of compound administration are described
below. Intravenous (IV) and oral (PO) routes of administration by far are the most
frequently used in discovery settings.
Single-Dose Bolus Administration
SINGLE-DOSE INTRAVENOUS ADMINISTRATION Intravenous administration allows for the
direct presentation of compound to the body with no loss of material. The disadvantage of IV administration is that it is invasive and may be more stressful for
animals. IV administration is usually used to determine some primary PK parameters
of the compound such as AUC, total clearance, the volumes of distribution, terminal
half-life, and others. The plasma AUC of the compound is frequently used as a
reference (the highest possible) value to determine bioavailability of the compound
after oral or other routes of administration.
The major limitation associated with IV administration is that the maximum dose
volume typically should not exceed 5 mL/kg. Due to this limitation, the maximum IV
dose that can be administered to animals depends on the compound solubility in
suitable vehicles. For example, if the solubility of the compound in a selected
formulation is 2 mg/mL, the maximum dose that can be achieved in a PK study is
going to be 10 mg/kg.
It is critica l for an IV study to select the most optimal time points for sample
collection, especially early time points, for compounds with a fast distribution
phase.
Drug administration PK sampling
Body
IV
IPV
EV:
PO, IP, SC, IM,IA, IT
ID
IG
Blood systemic
Bloodportal
Urine
Bile
Organs & Tissues
Figure 5.28 Potential routes of administration of the compounds and the sampling routes.
256
PHARMACOKINETICS FOR MEDICINAL CHEMISTS
https://t.me/medicina_free
SINGLE-DOSE ORAL ADMINISTRATION Single oral dose (usually via oral gavage) intro-
duces the compound directly into the animals stomach using a gavage needle attached
to a syringe. This administration is usually used to evaluate oral bioavailability
of newly synthesized compounds or compare different formulations of the same
compound.
The dose volume for oral gavage is as large as 20 mL/kg, and the selection of the
formulation suitable for dosing is much wider than for IV administration. Both
solution and suspension formulations can be used for PO dosing. It is very important
to evaluate the potential effect of the components of the formulation on the physiology
of the intestine in order to correctly estimate PK parameters.
INTRAPERITONEAL ADMINISTRATION An IP administration may provide an efficient
delivery for some compounds with low oral bioavailability. Most frequently, PK
studies with IP dosing are conducted in support of efficacy studies with the same route
of administration. The dose volume for IP administration usually should not exceed
20 mL/kg in the mouse and 10 mL/kg in the rat [97].
SC AND IM ADMINISTRATION Subcutaneous (under the skin) or intramuscular (into the
muscles) rout es of administration are less frequently used in discovery settings and
primarily conducted to support efficacy studies with the same route of administration.
IM administration is limited by the dose volume that can be delivered (1 mL/kg
[3]), the local irritation at the injection site, and is dependent on the excipients in the
formulation. Care should be taken with larger volumes and if necessary should be
administered in divided doses.
INTRATHECAL ADMINISTRATION A lumbar intrathecal (IT) injection is a method to
deliver compound into the cerebrospinal fluid (CSF), which may be a useful route of
administration for CNS-active compounds.
INTRA-ARTICULAR ADMINISTRATION The intra-articular (IA) route of administration is
a direct injection of compound into a joint. This type of dosing is used for some
rheumatoid arthritis studies.
OTHERS ROUTES OF ADMINISTRATION There are some less frequently used routes of
administration for PK studies such as hepatic-portal vein (HPV or IPV), oral gastric,
and intraduodenal dosing. Those routes of administration are usually used to
troubleshoot low oral bioavailability of the compounds.
IG ADMINISTRATION Intraga stric catheterization offers the advantage of an oral dose
without the stress and handling involved with conventional PO administration via
gavage needle or feeding tube.
HEPATIC-PORTAL VEIN ADMINISTRATION Hepatic-portal vein, sometimes called IPV
(intraportal vein) dosing is similar to IV dosing. The difference is that com pound
is delivered directly to the liver by introduction into the portal vein as opposed to the
PK PRACTICES 257
https://t.me/medicina_free
Соседние файлы в папке Библиотека им академика М.И. Перельмана