Guideline No. 100
Guidance for Industry: Impurities: Residual Solvents in New Veterinary Medicinal Products, Active Substances and Excipients: VICH GL18, Final Guidance
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
FOOD AND DRUG ADMINISTRATION
CENTER FOR VETERINARY MEDICINE
Guidance for Industry I
NEW VETERINARY MEDICINAL PRODUCTS,
ACTIVE SUBSTANCES AND EXCIPIENTS
VICH GL18
FINAL GUIDANCE
This final guidance recommends acceptable amounts for residual solvents in new animal drugs (referred to as pharmaceuticals or veterinary medicinal products in the guidance) for the safety of target animals as well as for the safety of human consumers of products derived from treated food producing animals. It is intended to assist in developing new animal drug applications (referred to as marketing applications in the guidance) submitted to the European Union, Japan and the United States.
Comments and suggestions regarding this document should be submitted to the Dockets Management Branch (HFA-305), Food and Drug Administration, 5630 Fishers Lane, Rm. 1061, Rockville, MD 20852, e-mail: fdadockets@oc.fda.gov Please refer to Docket No.99D-4071 when commenting on this document.
For questions regarding this final document contact Kevin J. Greenlees, Center for Veterinary Medicine, (HFV-153), Food and Drug Administration, 7500 Standish Place, Rockville, MD 20855, 301-827-6977, e-mail: kgreenle@cvm.fda.gov
.U.S. Department of Health and Human Services
Food and Drug Administration
Center for Veterinary Medicine
May 15, 2001
VICH GL18 (I
MPURITIES SOLVENTS)I
MPURITIESSO: LRVEESNITDSU AINLRecommended for Implementation
at Step 7 of the VICH Process
on 15 June 2000
by the VICH Steering Committee
|
T HIS GUIDANCE HAS BEEN DEVELOPED BY THE APPROPRIATE VICH EXPERT WORKING GROUP ON THE BASIS OFTHE ICH GUIDANCES ON THE SAME SUBJECT AND WAS SUBJECT TO CONSULTATION BY THE PARTIES, INACCORDANCE WITH THE VICH PROCESS. AT STEP 7 OF THE PROCESS THE FINAL DRAFT IS RECOMMENDED FORADOPTION TO THE REGULATORY BODIES OF THE EUROPEAN UNION, JAPAN AND USA. |
IMPURITIES: RESIDUAL SOLVENTS IN
NEW VETERINARY MEDICINAL PRODUCTS,
ACTIVE SUBSTANCES AND EXCIPIENTS
1. INTRODUCTION
2. SCOPE OF THE GUIDANCE
3. GENERAL PRINCIPLES
3.1 Classification of Residual Solvents by Risk Assessment
3.2 Methods for Establishing Exposure Limits
3.3 Options for Describing Limits of Class 2 Solvents
3.4 Analytical Procedures
3.5 Reporting Levels of Residual Solvents
4.1 Solvents that should be Avoided
4.2 Solvents that should be Limited
4.3 Solvents with Low Toxic Potential
4.4 Solvents For Which No Adequate Toxicological Data Was Found
APPENDIX 1: LIST OF SOLVENTS INCLUDED IN THE GUIDANCE
APPENDIX 2: ADDITIONAL BACKGROUND
A2.1 Environmental Regulation of Organic Volatile Solvents
A2.2 Residual Solvents in Pharmaceuticals
APPENDIX 3: METHODS FOR ESTABLISHING EXPOSURE LIMITS IMPURITIES: RESIDUAL SOLVENTS IN NEW VETERINARY MEDICINAL PRODUCTS, ACTIVE SUBSTANCES AND EXCIPIENTS This final guidance represents the agency's current thinking and does not create or confer any rights for or on any person and does not operate to bind FDA or the public. An alternative method may be used as long as it satisfies the requirements of applicable statutes and regulations
Table A.3.1: Values used in the calculations in this document
1. INTRODUCTION
The objective of this guidance is to recommend acceptable amounts for residual solvents in pharmaceuticals for the safety of the target animal as well as for the safety of residues in products derived from treated food producing animals. The guidance recommends use of less toxic solvents and describes levels considered to be toxicologically acceptable for some residual solvents.
Residual solvents in pharmaceuticals are defined here as organic volatile chemicals that are used or produced in the manufacture of active substances or excipients, or in the preparation of veterinary medicinal products. The solvents are not completely removed by practical manufacturing techniques. Appropriate selection of the solvent for the synthesis of active substance may enhance the yield, or determine characteristics such as crystal form, purity, and solubility. Therefore, the solvent may sometimes be a critical parameter in the synthetic process. This guidance does not address solvents deliberately used as excipients nor does it address solvates. However, the content of solvents in such products should be evaluated and justified.
Since there is no therapeutic benefit from residual solvents, all residual solvents should be removed to the extent possible to meet product specifications, good manufacturing practices, or other quality-based requirements. Veterinary medicinal products should contain no higher levels of residual solvents than can be supported by safety data. Some solvents that are known to cause unacceptable toxicities (Class 1, Table 1, page 9) should be avoided in the production of active substances, excipients, or veterinary medicinal products unless their use can be strongly justified in a risk-benefit assessment. Some solvents associated with less severe toxicity (Class 2, Table 2, page 9) should be limited in order to protect target animals and human consumers from potential adverse effects. Ideally, less toxic solvents (Class 3, Table 3, page 10) should be used where practical. The complete list of solvents included in this guidance is given in Appendix 1.
The list of solvents is not exhaustive and other solvents can be used and later added to the lists. Recommended limits of Class 1 and 2 solvents or classification of solvents may change, as new safety data becomes available. Supporting safety data in a marketing application for a new veterinary medicinal product containing a new solvent may be based on concepts in this guidance or the concept of qualification of impurities as expressed in the guidance for active substance (VICH GL 10, Impurities in New Veterinary Drug Substances) 1or veterinary medicinal product (VICH GL 11, Impurities in New Veterinary Medicinal Products) 2, or all three guidances.
Residual solvents in active substances, excipients, and in veterinary medicinal products are within the scope of this guidance. Therefore, testing should be performed for residual solvents when production or purification processes are known to result in the presence of such solvents. Manufacturers should test for solvents that are used or produced in the manufacture or purification of medicinal substances, excipients, or veterinary medicinal products. Although manufacturers may choose to test the veterinary medicinal product, a cumulative method may be used to calculate the residual solvent levels in the product from the levels in the ingredients used to produce the product. If the calculation results in a level equal to or below that recommended in this guidance, no testing of the veterinary medicinal product for residual solvents need be considered. If, however, the calculated level is above the recommended level, the veterinary medicinal product should be tested to ascertain whether the formulation process has reduced the relevant solvent level to within the acceptable amount. The veterinary medicinal product should also be tested if a solvent is used during its manufacture.
This guidance does not apply to potential new active substances, excipients, or veterinary medicinal products used during the clinical research stages of development, nor does it apply to existing marketed veterinary medicinal products.
The guidance applies to all dosage forms and routes of administration. Higher levels of residual solvents may be acceptable in certain cases or topical application. Justification for these levels should be made on a case by case basis.
See Appendix 2 for additional background information related to residual solvents.
3.1 Classification of Residual Solvents by Risk Assessment
The term "tolerable daily intake" (TDI) is used by the International Program on Chemical Safety (IPCS) to describe exposure limits of toxic chemicals and "acceptable daily intake" (ADI) is used by the World Health Organisation (WHO) and other national and international health authorities and institutes. The new term "permitted daily exposure" (PDE) is defined in the present guidance as a pharmaceutically acceptable intake of residual solvents to avoid confusion of differing values for ADIs of the same substance.
Residual solvents assessed in this guidance are listed in Appendix 1 by common names and structures. They were evaluated for their possible risk to human health and placed into one of three classes as follows:
Class 1 solvents:
Solvents that should be avoidedKnown human carcinogens, strongly suspected human carcinogens, and environmental hazards.
Class 2 solvents:
Solvents that should be limitedNon-genotoxic animal carcinogens or possible causative agents of other irreversible toxicity such as neurotoxicity or teratogenicity.
Solvents suspected of other significant but reversible toxicities.
Class 3 solvents:
Solvents with low toxic potentialSolvents with low toxic potential to man; no health-based exposure limit is needed. Class 3 solvents have PDEs of 50 mg or more per day.
3.2 Methods for Establishing Exposure Limits
The method used to establish permitted daily exposures for residual solvents is presented in Appendix 3. Summaries of the toxicity data that were used to establish limits are published in Pharmeuropa, Vol. 9, No. 1, Supplement, April 1997.
3.3 Options for Describing Limits of Class 2 Solvents
Three options are available when setting limits for Class 2 solvents.
Option 1: The concentration limits in ppm stated in Table 2 should be used. They were calculated using equation (1) below by assuming a product mass of 10 g administered daily.
Here, PDE is given in terms of mg/day and dose is given in g/day.
These limits are considered recommended for residual solvents in all substances, excipients, or products. Therefore this option may be applied if the daily dose is not known or fixed. If the residual solvents in all excipients and active substances in a formulation meet the limits given in Option 1, then these components may be used in any proportion. No further calculation is necessary provided the daily dose does not exceed 10 g. Products that are administered in doses greater than 10 g per day should be considered under Option 2.
Option 2: it is not considered necessary for residual solvents in each component of the veterinary medicinal product to comply with the limits given in Option 1. The PDE in terms of mg/day as stated in Table 2 should be used with the known maximum daily dose and equation (1) above to determine the concentration of residual solvent allowed in the veterinary medicinal product. Such limits are considered acceptable provided that it has been demonstrated that the residual solvent has been reduced to the practical minimum. The limits should be realistic in relation to analytical precision, manufacturing capability, reasonable variation in the manufacturing process, and the limits should reflect contemporary manufacturing standards.
Option 2 may be applied by adding the amounts of a residual solvent present in each of the components of the veterinary medicinal product. The sum of the amounts of solvent per day should be less than that given by the PDE.
Consider an example of the use of Option 1 and Option 2 applied to acetonitrile in a veterinary medicinal product. The permitted daily exposure to acetonitrile is 4.1 mg per day; thus, the Option 1 limit is 410 ppm. The maximum administered daily mass of a veterinary medicinal product is 5.0 g, and the veterinary medicinal product contains two excipients. The composition of the veterinary medicinal product and the calculated maximum content of residual acetonitrile are given in the following table.
|
Component |
Amount in formulation |
Acetonitrile content |
Daily exposure |
|
Active substance |
0.3 g |
800 ppm |
0.24 mg |
|
Excipient 1 |
0.9 g |
400 ppm |
0.36 mg |
|
Excipient 2 |
3.8 g |
800 ppm |
3.04 mg |
|
Veterinary medicinal product |
5.0 g |
728 ppm |
3.64 mg |
Excipient 1 meets the Option 1 limit, but the active substance, excipient 2, and the veterinary medicinal product do not meet the Option 1 limit. Nevertheless, the product meets the Option 2 limit of 4.1 mg per day and thus conforms to the recommendations in this guidance.
Consider another example using acetonitrile as residual solvent. The maximum administered daily mass of a veterinary medicinal product is 5.0 g, and the veterinary medicinal product contains two excipients. The composition of the veterinary medicinal product and the calculated maximum content of residual acetonitrile are given in the following table.
|
Component |
Amount in formulation |
Acetonitrile content |
Daily exposure |
|
Active substance |
0.3 g |
800 ppm |
0.24 mg |
|
Excipient 1 |
0.9 g |
2000 ppm |
1.80 mg |
|
Excipient 2 |
3.8 g |
800 ppm |
3.04 mg |
|
Veterinary medicinal product |
5.0 g |
1016 ppm |
5.08 mg |
In this example, the product meets neither the Option 1 nor the Option 2 limit. The manufacturer could test the product to determine if the formulation process reduced the level of acetonitrile. If the level of acetonitrile was not reduced during formulation to the allowed limit, then the manufacturer of the product should take other steps to reduce the amount of acetonitrile in the product or option 3 should be considered.
Option 3
Applicants may justify higher levels for the PDE and concentration limit based upon the actual daily dose, actual target species, and relevant toxicological data and considering consumer safety aspects. Use of Option 3 should be handled on a case by case basis by the regulatory authorities. This option may be applied as:
3a – The applicant may provide an appropriate body weight for the actual target species and / or the actual dose and recalculate the PDE and/or concentration limit using the ICH equations and ICH supporting toxicological data.
3b – The applicant may provide new toxicological data (with or without actual target animal and dose information) and recalculate the PDE and concentration limit using the equation provided by ICH.
If all of these steps fail to reduce the level of residual solvent, in exceptional cases the manufacturer could provide a summary of efforts made to reduce the solvent level to meet the guidance value, and provide a risk-benefit analysis to support allowing the product to be utilised with residual solvent at a higher level.
Residual solvents are typically determined using chromatographic techniques such as gas chromatography. Any harmonised procedures for determining levels of residual solvents as described in the pharmacopoeias should be used, if feasible. Otherwise, manufacturers would be free to select the most appropriate validated analytical procedure for a particular application. If only Class 3 solvents are present, a non-specific method such as loss on drying may be used.
Validation of methods for residual solvents should conform to the VICH guidances "Validation of analytical procedures: definition and terminology" and "Validation of analytical procedures: methodology."
3
Manufacturers of pharmaceutical products need certain information about the content of residual solvents in excipients or active substances in order to meet the criteria of this guidance. The following statements are given as recommended examples of the information that could be provided from a supplier of excipients or active substances to a pharmaceutical manufacturer.
The supplier might choose one of the following as appropriate:
Only Class 3 solvents are likely to be present. Loss on drying is less than 0.5%.
Only Class 2 solvents X, Y, ... are likely to be present. All are below the Option 1 limit. (Here the supplier would name the Class 2 solvents represented by X, Y, .)
Only Class 2 solvents X, Y, ... and Class 3 solvents are likely to be present. Residual Class 2 solvents are below the Option 1 limit and residual Class 3 solvents are below 0.5%.
If Class 1 solvents are likely to be present, they should be identified and quantified. "Likely to be present" refers to the solvent used in the final manufacturing step and to solvents that are used in earlier manufacturing steps and not removed consistently by a validated process.
If solvents of Class 2 or Class 3 are present at greater than their Option 1 limits or 0.5%, respectively, they should be identified and quantified.
4. LIMITS OF RESIDUAL SOLVENTS
4.1 Solvents that should be Avoided
Solvents in Class 1 should not be employed in the manufacture of active substances, excipients, and veterinary medicinal products because of their unacceptable toxicity or their deleterious environmental effect. However, if their use is unavoidable in order to produce a veterinary medicinal product with a significant therapeutic advance, then their levels should be restricted as shown in Table 1, unless otherwise justified. 1,1,1-Trichloroethane is included in Table 1 because it is an environmental hazard. The stated limit of 1500 ppm is based on a review of the safety data.+
3
In the U.S., these guidances can be found on the CVM home page (http://www.fda.gov/cvm) as guidance numbers 63 and 64.Table 1: Class 1 Solvents in pharmaceutical products (solvents that should be avoided)
|
Solvent |
Concentration Limit (ppm) |
Concern |
|
Benzene |
2 |
Carcinogen |
|
Carbon tetrachloride |
4 |
Toxic and environmental hazard |
|
1,2-Dichloroethane |
5 |
Toxic |
|
1,1-Dichloroethene |
8 |
Toxic |
|
1,1,1-Trichloroethane |
1500 |
Environmental hazard |
Solvents in Table 2 should be limited in pharmaceutical products because of their inherent toxicity. PDEs are given to the nearest 0.1 mg/day, and concentrations are given to the nearest 10 ppm. The stated values do not reflect the necessary analytical precision of determination. Precision should be determined as part of the validation of the method.
Table 2: Class 2 Solvents in Pharmaceutical Products
|
Solvent |
PDE (mg/day) |
Concentration Limit (ppm) |
|
Acetonitrile |
4.1 |
410 |
|
Chlorobenzene |
3.6 |
360 |
|
Chloroform |
0.6 |
60 |
|
Cyclohexane |
38.8 |
3880 |
|
1,2-Dichloroethene |
18.7 |
1870 |
|
Dichloromethane |
6.0 |
600 |
|
1,2-Dimethoxyethane |
1.0 |
100 |
|
N,N-Dimethylacetamide |
10.9 |
1090 |
|
N,N-Dimethylformamide |
8.8 |
880 |
|
1,4-Dioxane |
3.8 |
380 |
|
2-Ethoxyethanol |
1.6 |
160 |
|
Ethylene glycol |
6.2 |
620 |
|
Formamide |
2.2 |
220 |
|
Hexane |
2.9 |
290 |
|
Methanol |
30.0 |
3000 |
|
2-Methoxyethanol |
0.5 |
50 |
|
Methylbutylketone |
0.5 |
50 |
|
Methylcyclohexane |
11.8 |
1180 |
|
N-Methylpyrrolidone |
48.4 |
4840 |
|
Nitromethane |
0.5 |
50 |
|
Pyridine |
2.0 |
200 |
|
Sulfolane |
1.6 |
160 |
|
Tetralin |
1.0 |
100 |
|
Toluene |
8.9 |
890 |
|
1,1,2-Trichloroethene |
0.8 |
80 |
|
Xylene* |
21.7 |
2170 |
* usually 60% m-xylene, 14% p-xylene, 9% o-xylene with 17% ethyl benzene.
4.3 Solvents with Low Toxic Potential
Solvents in Class 3 (shown in Table 3) may be regarded as less toxic and of lower risk to target animal and human consumer health. Class 3 includes no solvent known as a human health hazard at levels normally accepted in pharmaceuticals. However, there are no long-term toxicity or carcinogenicity studies for many of the solvents in Class 3. Available data indicate that they are less toxic in acute or short-term studies and negative in genotoxicity studies. It is considered that amounts of these residual solvents of 50 mg per day or less (corresponding to 5000 ppm or 0.5% under Option 1) would be acceptable without justification. Higher amounts may also be acceptable provided they are realistic in relation to manufacturing capability and good manufacturing practice.
Table 3: Class 3 Solvents which should be limited by GMP or other quality-based requirements
|
Acetic acid |
Heptane |
|
Acetone |
Isobutyl acetate |
|
Anisole |
Isopropyl acetate |
|
1-Butanol |
Methyl acetate |
|
2-Butanol |
3-Methyl-1-butanol |
|
Butyl acetate |
Methylethyl ketone |
|
tert-Butylmethyl ether |
Methylisobutyl ketone |
|
Cumene |
2-Methyl-1-propanol |
|
Dimethylsulfoxide |
Pentane |
|
Ethanol |
1-Pentanol |
|
Ethyl acetate |
1-Propanol |
|
Ethyl ether |
2-Propanol |
|
Ethyl formate |
Propyl acetate |
|
Formic acid |
Tetrahydrofuran |
4.4 Solvents for Which No Adequate Toxicological Data Was Found
The following solvents (Table 4) may also be of interest to manufacturers of excipients, active substances, or veterinary medicinal products. However, no adequate toxicological data on which to base a PDE was found. Manufacturers should supply justification for residual levels of these and other solvents for which a PDE has not been established for use in pharmaceutical products.
Table 4: Solvents for which no adequate Toxicological Data was found
|
1,1-Diethoxypropane |
Methylisopropyl ketone |
|
1,1-Dimethoxymethane |
Methylisopropyl ketone |
|
2,2-Dimethoxypropane |
Petroleum ether |
|
Isooctane |
Trichloroacetic acid |
|
Isopropyl ether |
Trifluoroacetic acid |
Genotoxic carcinogens:
Carcinogens which produce cancer by affecting genes or chromosomes.LOEL:
Abbreviation for lowest-observed effect level.Lowest-observed effect level:
The lowest dose of substance in a study or group of studies that produces biologically significant increases in frequency or severity of any effects in the exposed humans or animals.Modifying factor:
A factor determined by professional judgement of a toxicologist and applied to bioassay data to relate that data safely to humans.Neurotoxicity:
The ability of a substance to cause adverse effects on the nervous system.NOEL:
Abbreviation for no-observed-effect level.No-observed-effect level:
The highest dose of substance at which there are no biologically significant increases in frequency or severity of any effects in the exposed humans or animals.PDE:
Abbreviation for permitted daily exposure.Permitted daily exposure:
The maximum acceptable intake per day of residual solvent in pharmaceutical products.Reversible toxicity:
The occurrence of harmful effects that are caused by a substance and which disappear after exposure to the substance ends.Strongly suspected human carcinogen:
A substance for which there is no epidemiological evidence in humans of carcinogenesis but there are positive genotoxicity data and clear evidence of carcinogenesis in rodents (or other animal species).Teratogenicity:
The occurrence of structural malformations in a developing fetus when a substance is administered during pregnancy.APPENDIX 1: LIST OF SOLVENTS INCLUDED IN THE GUIDANCE
APPENDIX 2: ADDITIONAL BACKGROUND
Several of the residual solvents frequently used in the production of pharmaceuticals are listed as toxic chemicals in Environmental Health Criteria (EHC) monographs and the Integrated Risk Information System (IRIS). The objectives of such groups as the International Programme on Chemical Safety (IPCS), the United States Environmental Protection Agency (USEPA), and the United States Food and Drug Administration (USFDA) include the determination of acceptable exposure levels. The goal is protection of human health and maintenance of environmental integrity against the possible deleterious effects of chemicals resulting from long-term environmental exposure. The methods involved in the estimation of maximum safe exposure limits are usually based on long-term studies. When long-term study data are unavailable, shorter term study data should be used with modification of the approach such as use of larger safety factors. The approach described therein relates primarily to long-term or life-time exposure of the general population in the ambient environment, i.e., ambient air, food, drinking water and other media.
A2.2 Residual Solvents in Pharmaceuticals
Exposure limits in this guidance are established by referring to methodologies and toxicity data described in EHC and IRIS monographs. However, some specific assumptions about residual solvents to be used in the synthesis and formulation of pharmaceutical products should be taken into account in establishing exposure limits. They are: Veterinary patients (rather than the general animal population) receive pharmaceuticals to treat their diseases or for prophylaxis to prevent infection or disease. However, there are some veterinary medicinal products which are used as aids in agricultural production which are unrelated to the presence of infection or disease in the animal population.
The assumption of life-time exposure of the veterinary patient is not necessary for most pharmaceutical products but may be appropriate as a working hypothesis to reduce risk to human health as a life-time exposure of the human consumer to the edible tissues of food animals treated with the veterinary medicinal product.
Residual solvents are unavoidable components in pharmaceutical production and will often be a part of veterinary medicinal products.
Residual solvents should not exceed recommended levels except in exceptional circumstances, and then should be justified.
Data from toxicological studies that are used to determine acceptable levels for residual solvents should have been generated using appropriate protocols including, but not necessarily limited to those described by OECD, EPA and the FDA Red Book.
The Gaylor-Kodell method of risk assessment (Gaylor, D. W. and Kodell, R. L.: Linear Interpolation algorithm for low dose assessment of toxic substance. J Environ. Pathology, 4, 305, 1980) is appropriate for Class 1 carcinogenic solvents. Only in cases where reliable carcinogenicity data are available should extrapolation by the use of mathematical models be applied to setting exposure limits. Exposure limits for Class 1 solvents could be determined with the use of a large safety factor (i.e., 10,000 to 100,000) with respect to the no-observed-effect level (NOEL). Detection and quantitation of these solvents should be by state-of-the-art analytical techniques.
Acceptable exposure levels in this guidance for Class 2 solvents were established by calculation of PDE values according to the procedures for setting exposure limits in pharmaceuticals (Pharmacopeial Forum, Nov-Dec 1989), and the method adopted by IPCS for Assessing Human Health Risk of Chemicals (Environmental Health Criteria 170, WHO, 1994). These methods are similar to those used by the USEPA (IRIS) and the USFDA (Red Book) and others. The method is outlined here to give a better understanding of the origin of the PDE values. It is not necessary to perform these calculations in order to use the PDE values tabulated in Section 4 of this document.
PDE is derived from the no-observed-effect level (NOEL), or the lowest-observed effect level (LOEL) in the most relevant animal study as follows:
The PDE is derived preferably from a NOEL. If no NOEL is obtained, the LOEL may be used. Modifying factors proposed here, for relating the data to humans, are the same kind of "uncertainty factors" used in Environmental Health Criteria (Environmental Health Criteria 170, World Health Organisation, Geneva, 1994), and "modifying factors" or "safety factors" in Pharmacopeial Forum. The assumption of 100% systemic exposure is used in all calculations regardless of route of administration.
The modifying factors are as follows:
F1 = A factor to account for extrapolation between species
F1 = 5 for extrapolation from rats to humans
F1 = 12 for extrapolation from mice to humans
F1 = 2 for extrapolation from dogs to humans
F1 = 2.5 for extrapolation from rabbits to humans
F1 = 3 for extrapolation from monkeys to humans
F1 = 10 for extrapolation from other animals to humans
F1 takes into account the comparative surface area: body weight ratios for the species concerned and for man. Surface area (S) is calculated as:
S = kM0.67
in which M = body mass, and the constant k has been taken to be 10. The body weights used in the equation are those shown below in Table A3.1.
F2
= A factor of 10 to account for variability between individuals
A factor of 10 is generally given for all organic solvents, and 10 is used consistently in this F3 = A variable factor to account for toxicity studies of short-term exposure
guidance.
F3 = 1 for studies that last at least one half lifetime (1 year for rodents or rabbits; 7 years
for cats, dogs and monkeys).
F3 = 1 for reproductive studies in which the whole period of organogenesis is covered.
F3 = 2 for a 6-month study in rodents, or a 3.5-year study in non-rodents.
F3 = 5 for a 3-month study in rodents, or a 2-year study in non-rodents.
F3 = 10 for studies of a shorter duration.
In all cases, the higher factor has been used for study durations between the time points, e.g. a factor of 2 for a 9-month rodent study.
F4
= A factor that may be applied in cases of severe toxicity, e.g. non-genotoxic carcinogenicity, neurotoxicity or teratogenicity. In studies of reproductive toxicity, the following factors are used:F4 = 1 for fetal toxicity associated with maternal toxicity
F4 = 5 for fetal toxicity without maternal toxicity
F4 = 5 for a teratogenic effect with maternal toxicity
F4 = 10 for a teratogenic effect without maternal toxicity
F5 = A variable factor that may be applied if the no-effect level was not established. When only an LOEL is available, a factor of up to 10 could be used depending on the severity of the toxicity. The weight adjustment assumes an arbitrary adult human body weight for either sex of 50 kg. This relatively low weight provides an additional safety factor against the standard weights of 60 kg or 70 kg that are often used in this type of calculation. It is recognised that some adult patients weigh less than 50 kg; these patients are considered to be accommodated by the built-in safety factors used to determine a PDE. As an example of the application of this equation, consider a toxicity study of acetonitrile in mice that is summarised in Pharmeuropa, Vol. 9, No. 1, Supplement, April 1997, page S24. The NOEL is calculated to be 50.7 mg kg
In this example,
F1 = 12 to account for the extrapolation from mice to humans
F2 = 10 to account for differences between individual humans
F3 = 5 because the duration of the study was only 13 weeks
F4 = 1 because no severe toxicity was encountered
F5 = 1 because the no effect level was determined
Table A.3.1: Values used in the calculations in this document
|
rat body weight |
425g |
mouse respiratory volume |
43 L/day |
|
pregnant rat body weight |
330g |
rabbit respiratory volume |
1440 L/day |
|
mouse body weight |
28g |
guinea pig respiratory volume |
430 L/day |
|
pregnant mouse body weight |
30g |
human respiratory volume |
28,800L/day |
|
guinea pig body weight |
500g |
dog respiratory volume |
9,000 L/day |
|
Rhesus monkey body weight |
2.5kg |
monkey respiratory volume |
1,150 L/day |
|
Rabbit body weight (pregnant or not) |
4kg |
mouse water consumption |
5 mL |
|
beagle dog body weight |
11.5 kg |
rat water consumption |
30 mL/day |
|
rat respiratory volume |
290 L/day |
rat food consumption |
30 g/day |
The equation for an ideal gas, PV = nRT, is used to convert concentrations of gases used in inhalation studies from units of ppm to units of mg/L or mg/m3. Consider as an example the rat reproductive toxicity study by inhalation of carbon tetrachloride (molecular weight 153.84) is summarised in Pharmeuropa, Vol, 9, No. 1, Supplement, April 1997, page S9.
The relationship 1000 L = 1 m 3 is used to convert to mg/ m3.
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