ISO 10993-16:2017 Biological evaluation of medical devices — Part 16: Toxicokinetic study design for degradation products and leachables

Foreword

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This document was prepared by Technical Committee ISO/TC 194, Biological and clinical evaluation of medical devices.

This third edition cancels and replaces the second edition (ISO 10993-16:2010), which has been technically revised with the following changes:

1. a) definition in 3.1 has been modified for clarification;
2. b) Clause 4 has been modified for clarification;
3. c) Clause 5 has been modified for clarification;
4. d) information regarding toxicokinetic studies on nano-objects have been added;
5. e) A.4 has been modified for clarification.

A list of all the parts in the ISO 10993 series can be found on the ISO website.

Introduction

Toxicokinetics describe the absorption, distribution, metabolism and excretion, with time, of foreign compounds in the body. Essential to the evaluation of the safety of a medical device is consideration of the stability of the material(s) in vivo and the disposition of intended and unintended leachables and degradation products. Toxicokinetic studies can be of value in assessing the safety of materials used in the development of a medical device or in elucidating the mechanism of observed adverse reactions. Toxicokinetic studies can also be applicable to medical devices containing active ingredients, in which case, pharmaceutical legislation are to be considered. The need for and extent of toxicokinetic studies should be carefully considered based on the nature and duration of contact of the device with the body (see A.2). Existing toxicological literature and toxicokinetic data can be sufficient for this consideration.

The potential hazard posed by a medical device can be attributed to the interactions of its components or their metabolites with the biological system. Medical devices can release leachables (e.g. residual catalysts, processing aids, residual monomers, fillers, antioxidants, plasticizers, etc.) and/or degradation products which migrate from the material and have the potential to cause adverse effects in the body.

A considerable body of published literature exists on the use of toxicokinetic methods to study the fate of chemicals in the body (see Bibliography). The methodologies and techniques utilized in such studies form the basis of the guidance in this document. Annex A provides a rationale for the use of this document.

1 Scope

This document provides principles on designing and performing toxicokinetic studies relevant to medical devices. Annex A describes the considerations for inclusion of toxicokinetic studies in the biological evaluation of medical devices.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

• ISO 10993-1 Biological evaluation of medical devices — Part 1: Evaluation and testing within a risk management process

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 10993-1 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

3.1 absorption

3.2 bioavailability

3.3 biodegradation

3.4 bioresorption

3.5 clearance

3.6 cmax

3.7 degradation product

3.8 distribution

3.9 excretion

3.10 extract

3.11 half-life

3.12 leachable

3.13 mean residence time

3.14 metabolism

3.15 test substance

3.16 tmax

3.17 volume of distribution

4.1

Toxicokinetic studies should be designed on a case-by-case basis, see Annex A.

4.2

A study protocol shall be written prior to commencement of the study. The study design, including methods, shall be defined in this protocol. Details of areas to be defined are given in 4.3 to 4.7 and in Clause 5.

4.3

The results of extraction studies (see ISO 10993-12 and ISO 10993-18) should be considered in order to determine the methods to be used for toxicokinetic studies. Information on the chemical and physicochemical properties, surface morphology of the material and biochemical properties of any leachable should also be considered.

NOTE

The extent and rate of release of leachables depend on the concentration at the surface, migration to the surface within the material, solubility and flow rate in the physiological milieu.

4.4

It is recommended to undertake toxicokinetic studies with a characterized leachable or degradation product that has the potential of being toxic. However, the performance of toxicokinetic studies on mixtures is possible under certain conditions. An extract liquid (see ISO 10993-12), or a ground or powdered form of the material or device, may be used in exceptional circumstances and shall be justified in the study design.

4.5

Analytical methods shall be able to detect and characterize degradation products, leachables and metabolites in biological fluids and tissues.

For analytical methods, other parts of ISO 10993 shall be used as relevant. The methods shall be fully described in the study report (see 5.1.10). Quantitative analytical methods shall be specific, sensitive and reproducible (see ISO 10993-18). Limit of detection/quantification shall be defined and justified.

Validation/qualification of the method shall be performed.

4.6

The study design shall state the physiological fluid, tissue or excreta in which analyte levels will be determined. Analyte recovery from the matrix shall be documented.

NOTE

Blood is convenient to sample and thus is often the fluid of choice for kinetic parameter and absorption studies. It is necessary to specify whether analysis is on whole blood, serum or plasma and to provide validation of this choice. Binding to circulating proteins or red cells can be determined in vitro.

4.7

There should be sufficient data points with adequate time intervals to allow determination of kinetic parameters. In theory, this should cover several terminal half-lives; in practice, the constraints of the analytical method may necessitate a compromise.

5.1.1

The study should be performed on an appropriate sex and species; consider utilizing the same species used for the systemic toxicity studies. The animal welfare conditions should be as recommended in guidelines for the care and use of animals (see ISO 10993-2).

5.1.2

A non-radiolabelled test substance may be utilized provided that suitable validated assay procedures for the test substance in the relevant samples exist and the metabolism of the test substance is well characterized.

5.1.3

If necessary, the test substance should be radiolabelled in a metabolically stable position, preferably with ¹⁴C or ³H, and of suitable radiochemical purity (>97 %). When using ³H, the possibility of tritium exchange should be considered. The specific activity and radiochemical purity of the test substance shall be known and reported.

5.1.4

The test substance should be administered by an appropriate route. This route should be relevant to the use of the medical device. The test substance should be prepared in a suitable vehicle taking into account the physicochemical properties of the test substance (leachable or degradation product) using appropriate route and dose of administration. The stability of the test substance in the vehicle shall be known and reported.

NOTE

The study design might require the inclusion of other route(s) for comparison of percent absorption.

5.1.5

In dose balance studies, animals should be housed only in metabolism cages.

5.1.6

Urine and faeces should be collected in low temperature vessels (or in vessels containing preservative that does not interfere with the analysis) to prevent post-elimination microbial or spontaneous modification. Blood for whole-blood or plasma analysis should be collected in the presence of a suitable anticoagulant.

5.1.7

Controls should, wherever possible, be collected prior to dosing. In some studies, collection of controls (e.g. tissues) is not possible from the test animals and these should be obtained from a control group.

5.1.8

Collection times should be appropriate to the type of study being performed, and may be carried out, as necessary, over periods of minutes, hours, days, weeks or even months. For studies involving excreta, this is usually a 24 h period over at least 96 h. Where blood sampling is required, blood is collected according to a specified schedule ranging from minutes to hours over a period up to 72 h.

5.1.9

Toxicokinetic studies should be performed in accordance with good laboratory practice.

5.1.10

The study report shall include the following information, where relevant:

1. a) strain and source of animals, age, sex (if females indicate reproductive state), environmental conditions, diet;
2. b) test substance and sample, purity, stability, formulation, amount administered;
3. c) test conditions, including route of administration;
4. d) assay methods, extraction, detection, validation/qualification;
5. e) overall recovery of material;
6. f) tabulation of individual results at each time point;
7. g) quality standard or good laboratory practice compliance statement;
8. h) presentation and discussion of results;
9. i) interpretation of results.

5.2.1.1

The study should be designed to provide the necessary information for risk assessment, and therefore it is usually not necessary to examine all aspects.

5.2.1.2

Absorption, distribution, metabolism and excretion studies are a range of studies capable of being performed either individually, examining one of these aspects, or collectively, examining several aspects in one study.

5.2.1.3

Depending on the design of the study, a number of kinetic parameters may be determined including absorption rate, area under the plasma concentration versus time curve, area under the first moment plasma concentration versus time curve, volume of distribution, c_max, t_max, half-life, mean residence time, elimination rate and clearance.

5.2.1.4

Kinetic parameters can only be determined for a particular molecular species and hence the assay needs to be specific and sensitive to this molecular species. True kinetic parameters of a relevant compound can only be determined following intravenous administration. It may therefore be necessary to include a limited intravenous administration study in the design of the kinetic parameter studies. This allows the fraction of the dose absorbed to be calculated and this serves as a correction in estimating parameters in other studies.

In some instances, intra-arterial administration should be considered as some compounds are known to be cleared through the pulmonary system.

5.2.1.5

The appropriate kinetic model should be used in determining the kinetic parameters. A number of computer programs exist for estimating kinetic parameters. The software should be validated prior to use and this validation should be documented. The assumptions entered into the program and the choices in modelling should be documented.

5.2.2 Absorption

Absorption depends on the route of administration, the physicochemical form of the test substance and the vehicle. It can be estimated from blood, serum, excreta and tissue concentrations. Bioavailability studies may be considered. The choice of the appropriate type of study depends on the other information required, availability of radiolabelled material and assay method. The absorption rate constant can be estimated reliably only if sufficient samples are taken in the absorption phase.

NOTE

In vitro methods exist which can give important information on gastrointestinal and dermal absorption of chemicals.

5.2.3.1

Distribution studies generally require radiolabelled compounds.

Studies may be

5.2.3.2

In general, sampling times in distribution studies may be based on kinetic data and will depend on test sample elimination. Multiple sampling times may be used. Sampling is normally more frequent in the early phase of absorption and elimination; however, samples need to be obtained over as much of the elimination phase as possible. The major determinant is often assay sensitivity.

5.2.4.1

Metabolism cages should permit a separate collection of urine and faeces throughout the study. The use of metabolic cages designed for the collection of CO₂ and volatile metabolites should be considered if relevant for the excretion. For studies of up to 14 d, the urine and faeces should be individually collected over 24 h intervals until the end of the experiment. In some study designs, animals may be sacrificed at intermediate times. Samples may be collected prior to 24 h when it is probable that the test substance or its metabolites will be rapidly excreted. For studies of longer duration, sampling over the initial period should occur as for the short-term studies. Thereafter, samples should be obtained for a continuous 24 h period per assessment period.

NOTE

The use of metabolism cages for prolonged periods might be detrimental to animal welfare. Therefore, at the longer times, representative discontinuous samples can be collected and these results extrapolated to continuous sampling.

5.2.4.2

The carcasses and/or target organs of the individual animals should be retained for analysis, and blood collected for analysis of plasma and whole-blood concentrations. After collection of the samples from the metabolism cages at the sacrifice time, the cages and their traps should be washed with an appropriate solvent. The resulting washes can be pooled and a representative fraction retained for analysis.

5.2.4.3

The recovery or calculated recovery of a test substance should ideally be (100 ± 10) % when a radiolabelled compound is used. The recovery range specified might not be achievable in all cases, and reasons for any deviation should be stated and discussed in the report. The amount of test substance in each fraction should be analysed by suitably validated procedures for either a radiolabelled or non-radiolabelled compound in the appropriate milieu. Where a radiolabelled compound is used, both parent compound and metabolites are assessed unless a specific assay is used.

5.2.4.4

Levels of radioactivity in the biological milieu should be determined, for example, by liquid scintillation counting; however, it should be stressed that this represents a mixed concentration of compound and metabolites, and no kinetic parameters can be derived from it. Where isolation of metabolites is considered necessary, this may involve a number of extractions and chromatographic procedures (e.g. high-pressure liquid chromatography, thin layer chromatography, gas-liquid chromatography), and the resulting material should be characterized by chemical methods and a variety of physical chemistry techniques (e.g. mass spectrometry, nuclear magnetic resonance spectroscopy).

5.2.4.5

The use of tissues, cells, homogenates and isolated enzymes for the study of metabolism in vitro is well documented. These methods identify potential metabolism which may not occur in vivo unless the compound is available at the appropriate site. The extents and rates of metabolism in vitro compared to in vivo will often differ.

A.1

Potential hazards exist in the use of most medical devices. Chemical characterization identifies chemical hazards (for potential risks, see ISO 10993-18 and ISO 14971) and should precede toxicokinetic considerations. However, it is neither necessary nor practical to conduct toxicokinetic studies for all identifiable intended and unintended leachables and degradation products, nor for all medical devices.

A.2

The need for toxicokinetic studies as part of the biological evaluation of a medical device shall be considered taking into account the final product and its constituent chemicals, intended and unintended leachables and degradation products in combination with the intended use of the device, e.g. nature and duration of contact.

Possible toxicokinetic interaction between active ingredients and leachables and/or degradation products should also be considered.

A.3

In vitro methods, which are appropriately validated, reasonable and practically available, reliable and reproducible, shall be considered for use in preference to in vivo tests (see ISO 10993-1). Where appropriate, in vitro experiments (e.g. tissue, homogenates or cells) should be conducted to investigate probable rather than possible degradation products. ISO 10993-2 applies to any in vivo testing being considered.

A.4

Toxicokinetic studies shall be considered if the following conditions are met:

1. a) the device is designed to undergo bioresorption;
2. b) the device is a permanent contact implant, and significant corrosion (of metallic materials) or biodegradation is known or likely, and/or migration of leachables from the device occurs;
3. c) substantial quantities of potentially toxic degradation products and leachables are likely or known to be released from a medical device into the body during clinical use;
4. d) substantial quantities of active ingredients/components are likely or known to be released from a medical device;
5. e) substantial quantities of nano-objects are likely or known to be released from a medical device into the body during clinical use.

NOTE 1

The meaning of the term “substantial quantities” is dependent on the properties of the chemicals/nano-objects in question.

NOTE 2

See ISO/TR 10993-22 for information on toxicokinetic studies on nano-objects.

A.5

Considerations for toxicokinetic studies are not required if

1. a) sufficient toxicological data or toxicokinetic data relevant to the degradation products and leachables already exist;
2. b) sufficient toxicological data or toxicokinetic data relevant to the active ingredients already exist;
3. c) the achieved or expected rates of release of degradation products and leachables from a particular device have been judged (see ISO 10993-17) to demonstrate safe levels of clinical exposure;
4. d) clinical exposure of degradation products and leachables is documented as safe with reference to historical experience.

A.6

Where materials are complex and contain products which are either endogenous or they are so similar to endogenous products that they cannot be analytically distinguished, a toxicokinetic study is usually not feasible.

Bibliography