Dept. Of P’Ceutical Sciences, Saurashtra University,

Rajkot

OECD GUIDELINE FOR THE TESTING OF CHEMICALS (417)

Toxicokinetics By

Chirag PatelM Pharm Sem II

INTRODUCTION Adopted on 22nd July 2010 Studies examining the toxicokinetics (TK) of a chemical

substance are conducted to obtain adequate information on its absorption, distribution, biotransformation (i.e. metabolism) and excretion, to aid in relating concentration or dose to the observed toxicity, and to aid in understanding its mechanism of toxicity.

Toxicokinetic studies may provide useful information for determining dose levels for toxicity studies (linear vs. non-linear kinetics), route of administration effects, bioavailability, and issues related to study design. Certain types of TK data can be used in physiologically based toxicokinetic (PBTK) model development.

INITIAL CONSIDERATIONS

Competent authorities have different requirements and needs regarding the measurement of endpoints and parameters related to toxicokinetics for different classes of chemicals (e.g. pesticides, biocides, industrial chemicals).

LIMITATIONS

This Test Guideline is not designed to address special circumstances, such as the pregnant or lactating animal and offspring, or to evaluate potential residues in exposed food-producing animals.

However, the data obtained from a TG 417 study can provide background information to guide the design of specific studies for these investigations.

This Test Guideline is not intended for the testing of nanomaterials. A report on preliminary review of OECD Test Guidelines for their applicability to nanomaterials indicates that TG 417 may not apply to nanomaterials (1).

ANIMAL WELFARE CONSIDERATIONS

Guidance on humane treatment of animals is available in OECD Guidance Document (GD) 19 (2).

It is recommended that OECD GD 19 be consulted for all in vivo and in vitro studies described in this Test Guideline.

DESCRIPTION OF THE METHODS

Pilot Studies The use of pilot studies is recommended and encouraged for the selection of experimental parameters for the toxicokinetics studies (e.g. metabolism, mass balance, analytical procedures, dose-finding, exhalation of CO2, etc.). Characterization of some of these parameters may not necessitate the use of radiolabelled substances.

Animal Selection -Species -Age and Strain (6 to 12 weeks) -Number and Sex of Animals(four males and

four females ) -Housing and feeding conditions Test Substance A radiolabelled test substance using 14C should be

used for all mass balance and metabolite identification aspects of the study.

Dose Selection Pilot Study

Usually a single oral dose is sufficient for the pilot study. The dose should be non-toxic, but high enough to allow for metabolite identification in excreta (and plasma, if appropriate) as well as to meet the stated purpose of the pilot study

Main StudiesFor the main studies, a minimum of two

doses is preferred since information gathered from at least two dose groups may aid in dose setting in other toxicity studies, and help in the dose-response assessment of already available toxicity tests.

Where two doses are administered, both doses should be high enough to allow for metabolite identification in excreta (and plasma, if appropriate). Information from available toxicity data should be considered for dose selection.

Measurements :-Mass Balance -Absorption

% Absorption = (Amount in bile + Urine + Expired air + Carcass without GI tract contents) / Amount administered x 100

-BioavaibilityF = ( AUCexp / AUCIV ) x ( DoseIV / Doseexp )

-Tissue Distribution -Metabolism -Excretion

Time Course Studies • Plasma/Blood Kinetics • Other Tissue Kinetics Reason for this other tissue kinetics includes -Evidence of extended blood half-life,

suggesting possible accumulation of test substance in various tissues or

-Interest in seeing if a steady state level has been achieved in specific tissues

• Enzyme Induction/Inhibition

SUPPLEMENTAL APPROACHESSupplemental approaches beyond the in

vivo experiments described in this Test Guideline may provide useful information on the absorption, distribution, metabolism or elimination of a chemical in certain species.

• Use of in vitro information• Use of Toxicokinetic Data from Toxicity

Studies as Complementary Information• Use of Toxicokinetic Modelling

DATA AND REPORTING It is recommended that the study report include a table of contents.

Body of the Report The body of the report should include information covered by this Test Guideline organized into sections and paragraphs as follows:

-Summary -Introduction -Materials and Methods

(a) Test Substance(b) Test Animals(c) Methods

MethodsIt should include a description of: (1)Justification for any modification of route of exposure and

exposure conditions, if applicable; (2) Justification for selection of dose levels; (3) Description of pilot studies used in the experimental

design of the follow-up studies, if applicable. Pilot study supporting data should be submitted;

(4) How the dosing solution was prepared and the type of solvent or vehicle, if any, used;

(5) Number of treatment groups and number of animals per group;

(6) Dosage levels and volume (and specific activity of the dose when radioactivity is used);

(7) Route(s) and methods of administration;

(8) Frequency of dosing; (9) Fasting period (if used); (10) Total radioactivity per animal; (11) Animal handling; (12) Sample collection and handling; (13) Analytical methods used for separation,

quantitation and identification of metabolites; (14) Limit of detection for the employed methods; (15) Other experimental measurements and

procedures employed (including validation of test methods for metabolite analysis).

(d) Statistical Analysis If statistical analysis is used to

analyze the study findings, then sufficient information on the method of analysis and the computer program employed should be included, so that an independent reviewer/statistician can re-evaluate and reconstruct the analysis.

Results All data should be summarized and tabulated with

appropriate statistical evaluation and described in the text of this section.

Radioactivity counting data should be summarized and presented as appropriate for the study, typically as microgram or milligram equivalents per mass of sample, although other units may be used.

This section should include graphic illustrations of the findings, reproduction of representative chromatographic and spectrometric data, metabolite identification/quantification and proposed metabolic pathways including molecular structure of metabolites.

Discussion and Conclusions In this section the author(s) should: (1) Provide a proposed metabolic pathway based on the results of the

metabolism and disposition of the test substance; (2) Discuss any potential species and sex differences regarding the

disposition and/or biotransformation of the test substance; (3) Tabulate and discuss the identification and magnitude of

metabolites, rates of clearance, bioaccumulation potential, and level of tissue residues of parent, and/or metabolite(s), as well as possible dose-dependent changes in TK parameters, as appropriate;

(4) Integrate into this section any relevant TK data obtained in the course of conducting toxicity studies;

(5) Provide a concise conclusion that can be supported by the findings of the study;

(6) Add Sections (as needed or appropriate) Additional sections should be used to include supporting

bibliographic information, tables, figures, appendices, etc.

ThAnK YoU