Toxicokinetic evaluation in preclinical studies. m.pharm 2nd sem pharmacology topic.

1. Toxicokinetic evaluation in preclinical studies
INSTITUTE OF PHARMACEUTICAL SCIENCES
KURUKSHETRA UNIVERSITY, HARYANA
Topic
Submitted to –
MS. Prabjeet Kaur
Submitted by –
Arshi Khanam
M.PHARM 2nd sem
(Pharmacology)

2. What is Toxicokinetics?
Toxicity + kinetics = kinetics of toxic substance.
Kinetics stand for how a drug or toxic substance affected by body in terms of
ADME.
Toxicokinetics TK is study as the application of pharmacokinetics to doses used
in testing of toxicology. A (NCE) new chemical entity as part of the safety
evaluation target organ toxicity in 2 or 3 animal species, to finding range-finding,
acute & pivotal toxicity studies are occur Characterize the target organ toxicity
and safety in 3-2animals.

3. Toxicokinetic assessment is both a monitoring or scientific necessity
in the drug advancement method. Toxicokinetic is the age of dynamic
data to evaluate systemic introduction, either as an essential part of
preclinical toxicity studies, or in specifically planned supportive
studies. These information help to comprehend the connection
between detected toxicity or administered dose. They additionally
assume a role in the clinical setting, supporting in the setting of
plasma limits for early human introduction and in the estimation of
protection limits.

4. Toxicokinetics is defined by the ICH as the generation of
pharmacokinetics data, either as an integral component in the
conduct of non-clinical toxicity studies. The need for
toxicokinetic data and the extent of exposure assessment in
individual toxicity studies should be based on a flexible step
by step approach. Choice of species and treatment regimen
used in non clinical studies. Lastly, information on systemic
exposure of animals during repeated-dose toxicity studies in
essential for the interpretation of study results.

6. Objectives of toxicokinetics
The primary objective of toxicokinetics is:
• to describe the systemic exposure achieved in animals and its relationship to dose level and the
time course of the toxicity study.
Secondary objectives are:
• to relate the exposure achieved in toxicity studies to toxicological findings and contribute to the
assessment of the relevance of these findings to clinical safety.
• to support the choice of species and treatment regimen in non-clinical toxicity studies.
• to provide information which, in conjunction with the toxicity findings, contributes to the
design of subsequent non-clinical toxicity studies.

7. Principle of toxicokinetics
The application of a toxicokinetics program can be done in a fact which will make easy protocol
design and dosing regimen extract and explanation of safety determination by toxicologist outside
of compromising the primary target of the study. For example-The blood sample of satisfactory
number should be assembled in sequence to measure suitable pharmacokinetics parameters-
mainly Tmax, AUC,& T1/2 later oral dosing & also Vdss, CLT later intravenous dosing –without
put in change the wellness of the animals & accurate reading in the toxicity of data.
It should be noted that for those toxicity studies whose performance is subject to Good
Laboratory Practice (GLP) the concomitant toxicokinetics must also conform to GLP.
Toxicokinetic studies retrospectively designed to generate specific sets of data under conditions
which closely mimic those of the toxicity studies should also conform to GLP when they are
necessary for the evaluation of safety.

8. Principles include in toxicokinetics are-
Quantification and Extent Of Exposure
Setting of the dose levels
 Route of Administration
Sampling Points
 Dose Level Setting
 Metabolite Determination
Statistical evaluation of data
Reporting

9. To check sufficient outlook to the NCE in the vital toxicity studies.
To measure the time course of this outlook.
To measure the connection between the dose and the expanse of
absorption of the NCE,
To determine the variety in the pharmacokinetics of the NCE upon
multiple dosing.
To measure a possibility connection between exposure (AUC
&Cmax) & toxicity finding.
The toxicokinetics studies include-

10. Terms used in toxicokinetics/pharmacokinetics
Cmax - A maximum concentration of compound observed in the matrix of interest.
Tmax- A time of maximum concentration.
T(1/2)- The time it takes for the concentration of the compound to reduce by 50%.A Half-life is
secondary pharmacokinetic parameter that is measured by the clearance (CL) & volume of distribution
(V) of the compound.
FORMULA= t1/2 =O.693×V /CL
AUC- The area under the concentration vs time curve.
Clearance (Cl)- The volume of fluid (usually blood) from which compound is removed completely
per unit time. Body Organs that might be elaborate in clearance: GI tract, Liver, Kidney, Lungs, Other
sites (e.g. blood or skin).
Volume of Distribution at Steady-State (Vdss)- A parameter that related plasma concentration to
total mass of compound in the body.

11. ADME
Absorption is process by which the chemical enters the body. It depends on the route of
administration. Such as oral , dermal and inhalation. Absorption have some important parameters
like bioavailability the membrane transportations etc. after that drug reach to the systemic
circulation.
Distribution is defined as the apparent volume into which a substance is distributed. Volume of
distribution is calculated from the dose taken and resulted plasma concentrations. Factors that
determined distributions are protein binding, plasma concentration, physiological barriers.
Vd= dose/ plasma concentration
Metabolism or the biotransformation is biochemical transformation of chemical.in this process
the chemical turned into more water soluble compound that can be eliminated rapidly. This can
produce pharmacologically active as well in active molecule.
Excretions is final elimination of the chemical from the body.

13. Measuring toxicokinetics: factors to
consider
Plasma (common) versus whole-blood or serum (less common) measurements. Whole blood is
the matrix of choice for drugs with variable kinetics (e.g. cyclosporin) as it gives a better
indication of cellular accumulation.
Unbound drug versus bound drug. Unbound drug in plasma is the most relevant indirect
measure of tissue concentration. It has been reported that similar exposure of a drug was noted at
a low toxic level in rat, dog and monkey compared to humans, using area under the curve (AUC)
measurements of total drug (i.e. with no safety margin). However, unbound drug exposure was
>20-fold the safety margin.
Exposure based on active entity and not salt (assume dissociation to the active form occurs in
blood).
Racemate versus enantiomer analyte. A method for chiral conversion might be needed early in
development.

14.  Non-linear dose kinetics; for example, increased exposure owing to saturation of a clearance
process or a long plasma half-life, or decreased exposure owing to auto-induction of metabolizing
enzymes.
Parent (always) versus metabolite(s) (rarer) analysis.
 Pro-drugs, where the metabolite is the active material (e.g. cyclosporin, enalapril, levodopa and
cyclophosphamide).
 Drug is metabolized to pharmacological or toxicological metabolites that contribute to the
overall response.
When extensive metabolism occurs and the measurement of a major metabolite is the only
measure for estimating exposure.
 Human metabolites not found in animal studies.

15. preclinical studies of toxicants have-
1.Safety pharmacology studies
Core studies in safety pharmacology comprise in vivo CNS, cardiovascular and respiratory
assessments. Although toxicokinetic assessment is not specifically mentioned in the guidelines,
it enables researchers to correlate any observed effects with systemic level of the drug.
However, it is possible to cross-reference dose level with exposure in toxicity studies.
2.Single-dose and rising-dose toxicity studies
Single-dose studies are usually performed in rodents. Although toxicokinetic evaluation is not
routinely included in such studies, plasma samples can be taken and stored for later analysis.
However, toxicokinetics can be assessed for some drug classes, or in screening studies (e.g. in a
series of candidates or when choosing a suitable formulation). Rising-dose studies are
performed in non-rodent models. Here, toxicokinetic evaluation takes place at various time-
points for each new dose level. Such an evaluation is especially useful if higher-dose emesis
occurs as it can reveal whether exposure to the drug still occurred

16. 3.Further repeat-dose toxicity studies-
Further repeat-dose studies are usually performed in rodents and non-rodents for up to six and
12 months, respectively, to enable longer clinical exposure. Assessment often occurs in a similar
way to shorter-term toxicity studies, although it is possible to reduce sampling times because
the drug profile is known from earlier studies. Both parent drug and metabolites can be
assessed.
4.Reproduction toxicity studies-
Reproduction toxicity measurements are taken in studies of fertility (rat), embryo-foetal
development (rat and rabbit) and peri- or post-natal development (rat). There is a regulatory
expectation for toxicokinetic data in pregnant animals, although no specific guidance is given.
Data from non-pregnant animals is useful to set dose levels, and the limitation of exposure is
usually governed by maternal toxicity.

17. 5.Genotoxicity studies-
Drug development usually needs to be supported by two in vitro studies and one in vivo study.
In vivo investigations usually use a rodent micronucleus (bone marrow or peripheral
erythrocytes) test or chromosome aberration (bone marrow cells) test. There is a regulatory
expectation to demonstrate exposure to the drug either with toxicity or toxicokinetic data. In
rodents, specific toxicokinetic evaluation might not be necessary as it is possible to cross-
reference with toxicity studies.
6.Carcinogenicity studies-
Lifetime studies in the rodent are needed to support the long-term clinical use of
pharmaceuticals. Dose selection is usually determined as the maximum tolerated dose (MTD),
which is a 25-fold AUC ratio (rodent to human), or by dose-limiting pharmacodynamics effects,
saturation of absorption, or a maximum feasible dose.

18. Applications of toxicokinetics
 A scenario of drug kinetics and metabolism more accurate.
Improved strategy assessment with more efficiency.
The fewer animals used and provide superior data for risk assessment purposes.
In preclinical/early clinical development risk programs at rescue.
At early stages proactively screen/ evaluate leads using predictive tools for
toxicity and mechanism of action.
A pre-clinical biomarkers of toxicity & drug response developed.
To improve the therapeutic outcomes adoption of toxicity management
approaches.

19. The studies of pre-clinical or clinical studies that are focused on research of
mechanism of drug toxicity (including kinetics of toxicants) and adverse drug
reactions (ADR) using toxicokinetics will be of high interest.
The application of toxicokinetics in safety of preclinical drug evaluation and
biomarkers identification.
The role of toxicokinetics in pharmacokinetics and modified medicine.
The toxicokinetics purpose of dosage selection, each toxic expression should be
separately analyzed and a correlation sought between each amount of exposure
that best reflects the mechanism of the related toxic effect& pathogenesis.

20. Conclusion
Interpreting preclinical data from the range of studies performed during drug
development requires a good understanding of the observed toxic response(s) versus
drug exposure. This understanding is crucial for setting safe dose levels for clinical use
of a potential new drug. Both species and sex-differences exist in animal toxicity studies
for toxicokinetic measurements, which obviously has relevance to the clinical
evaluation. A lack of dose proportionality also has relevance to the clinical use of a drug
and can be related to saturated mechanisms or auto-induction. Another important factor
is the effect of higher plasma values observed later in a toxicity study, possibly caused
by accumulation from a long half-life, reduced clearance, metabolizing-enzyme
inhibition or enterohepatic re-circulation. Clearance can be affected either by capacity-
limited elimination or impairment of hepatic function (e.g. with proxicromil). Although
toxicokinetic evaluation is only a small part of the process of understanding the fate of a
drug, it has a vital role to play in drug development – a role that continues to advance.

21. Thank you!