Test substances formulations

The test substance may be acquired in a number of ways. One common method is to purchase the product from a chemical dealer. This method of acquiring the test substance for a worker exposure or re-entry study allows one to proceed rapidly with the execution of the field portion of the study without the serious delays encountered while waiting for a test substance to be manufactured, assayed, and shipped to the site. Although having a test substance formulation which has been assayed under GLP standards and for which a certificate of analysis has been shipped to the test site is desirable, there are several instances when this is not practical. For example, one may encounter a worker exposure study where the pesticide to be evaluated is sold only in mini-bulk or even large bulk quantities holding as much as 2000 gal. In this case, duplicate 5-10-g or 5-10-mL retainer samples should be taken from the bulk or mini-bulk tanks for assay after the worker exposure study is in progress. 

The formulated product of the test substance should be prepared as a representative formulation for registration (or a formulation of similar composition), and applied to the test plants according to the use pattern indicated in the documents for registration. If several different use patterns are indicated in the documents for registration, studies should be conducted on each. 

The formulation to be tested at each site must be evaluated in the light of test substances with multiple formulation usages and geographical requirements. 

End-use formulations should be used as the test substance. If an active ingredient is marketed in two commercial formulations, then both should be used in the study, since there may be differences in residue levels and dissipation rates, e.g., a wettable powder versus a liquid formulation. The best solution would be plots located at the same site for a side-by-side comparison. This should only be necessary at one of the sites. However, each formulation should be represented in the study unless a strong case can be made for a worst-case scenario. 

The test substance is generally defined as the formulated pesticide product which is being applied to a crop or field and for which worker exposure is being assessed. 

A reference substance can be either the formulated test substance suspended in water or the technical or analytical grade active ingredient of the test substance dissolved in a solvent. The reference substance is normally used to fortify field matrices to develop information on the field storage stability of the active ingredient. Reference substances should be prepared at the analytical facility where the matrix samples are to be analyzed. Methods to prepare reference substances for field use will be discussed later. 

These principles lead to the conclusion that each test substance requires an individual formulation. Sometimes different ingredients will be required for different concentrations to obtain the maximum rate of release. No universal vehicle is available for any route, but a number of approaches are. Any dosage preparation lab should be equipped with glassware, a stirring hot plate, a sonicator, a good homogenizer, and a stock of the basic formulating material, as detailed at the end of this chapter. 

Ideally, only the 100% pure sample should be tested however, impurity-free samples are difficult to obtain and preparation of formulations (as previously discussed) is frequently essential. The toxicity of impurities or formulation components should be examined separately if the investigator feels that they may contribute significantly to the toxicity of the test substance. 

Several studies were conducted in which only a single high dose of 2-hexanone was orally administered to rats in an attempt to induce and consequently study the resulting neurotoxic effects. In addition, only a few of the studies were conducted using 2-hexanone of a stated purity of 96% or better. Other studies used a formulation containing 70% 2-hexanone or the purity of the test substance was not stated. As a result, the usefulness of the existing data base using the oral route is limited. 

Slow release formulations are available for tried and tested substances, e.g. ketoprofen and naproxen, if increased duration of effect is needed. 

When the test substance is formulated in a vehicle for gavage administration, consideration needs to be given to the consequences of the vehicle and the method of administration (i.e., single-daily administration, as opposed to sustained intake of food over the... 

The control group(s) should be housed and handled in an identical manner to the treated groups. Precautions may be necessary to prevent cross-contamination of the control animals with the test substance. This problem is particularly troublesome when a powdered diet formulation is used, which tends to spread contaminated dust all around the animal room. 

Experimental design (human study details or strain, number of animals per exposure/control group, sex, dose administration details) The purpose of this study was to determine the 13-week oral toxicity profile of diazinon in male and female beagle dogs. Diazinon was added to standard canine ration at concentrations of 0, 0.1, 0.5, 150, and 300 ppm. The test substance was the MG-8 formulation of diazinon (87.7% pure) mixed with feed and adjusted for purity. The concentrations of diazinon in the feed were determined during weeks 1, 3, 5, 9, and 13. Each dog was supplied with approximately 400 g of food daily. The corresponding doses, in mg/kg, were calculated by the authors to be 0.0034, 0.02, 5.9, and... 

The method of test substance synthesis or its source should be made a part of the documentation. This would apply to any test chemical, whether it is a technical material, a formulation, a metabolite, a by-product, or a radiolabeled compound. Any inpurities greater them... 

When making a choice of test situations, some investigators are biased by the effects of the tested substance in adulthood. Based on this knowledge, it is possible to formulate and test a specific hypothesis about aspects of brain and behavioral development that are expected to be affected. For instance, haloperidol can be expected to alter development of the dopamine system and motor activity, whereas clonidine can be expected to affect development of the catecholamine system and REM sleep. 

A self-reactive substance or mixture is regarded as possessing explosive properties when in laboratory testing the formulation is liable to detonate, to deflagrate rapidly or to show a violent effect when heated under confinement. 

The first step in the laboratory study of developmental toxicity is determination of the substance to be tested. This might be straightforward in drug or pesticide registration studies because only a single pure compound is of concern. In the case of complex mixtures, however, selection of the test substance(s) for the particular condition(s) and route(s) of exposure can be very difficult. For example, gasoline, diesel fuel, or aviation fuel each contain more than 250 diverse hydrocarbons, which change with source of the crude oil, the products are formulated differently... 

Injection 3 The test substance at the selected concentration formulated in a 1 1 mixture (v/v) of FCA/water or physiological saline. 

Pharmacopoeial identity tests are IR for the trihydrate and TLC for formulated products in the USP (except for co-formulations with clavulanate, where HPLC is used) IR, TLC and a colourimetric test for the drug substances in the BP and EP various combinations of IR, TLC and colourimetric tests for formulated products in the BP and BP(Vet.). 

In general, a simple formulation is used to deliver the test substance to the experimental animals. This formulation is usually not the same as the final market formulation and any manufacturing process changes made during the course of the different development phases of the product should always be evaluated with respect to earlier data obtained. Product comparability will need to be established. Previous data may no longer be (fully) representative and sometimes parts of the preclinical (or even early clinical) studies have to be repeated, replaced or annexed by additional studies. Obviously, in view of time and costs involved, one would like to avoid this kind of situation as much as readily possible. 

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