Test substances characterization

The test substance used in a field residue study must be clearly defined and properly identified to ensure that the correct chemicals are used for the study. This process is called test substance characterization (40 CFR 160.105). The characterization of a test substance includes confirming the test substance is what was intended and that the test substance represents the actual commercial product that will be marketed. The test substance may be acquired from either a commercial production run or from... 

Purity analysis and characterization of the test substance should be performed for each lot. A retention sample from each batch of the test substance should be archived. All unused test substance and partially empty containers should be retained until the final report is signed, unless a prior waiver has been obtained from the EPA. 

Test Substance Characterization (160.105) determine the identity, strength, purity and composition which define the test substance before its use in the study. 

Worker safety studies are not likely to normally include a control substance (i.e., a material used in the study to serve as basis of comparison with the test substance). However, if a control substance is included as a treatment group, then it must (1) be fully characterized as to its identity, purity (or strength), and stability (and solubility, if appropriate) (2) be appropriately tested in mixtures with any carrier used and (3) meet all the other GLP recordkeeping, labeling, and storage requirements, as specified for the test substance. There is some regulatory relief here, however, in that water, by definition, is excluded from being considered a control substance, and vehicles (those substances added to enhance solubilization or dispersion of the test substance) are addressed separately in the FIFRA GLP Standards. 

Test substances (or articles), control substances (or articles), and reference substances are covered by Subpart F in both the FDA and EPA regulations. Basically this subpart covers all substances under investigation and all known substances used in the investigation in terms of their characterization, handling, and mixing. 

Figure 2.5. Setup for in vitro measurement of blood-brain barrier permeability with a co-culture of bovine brain microvascular endothelial cells (BBMEC) and an astro ioma cell line, C6. The BBMEC are grown on top of a filter insert. The C6 cells are either grown on the opposite side of the filter or on the bottom of the wells. Transport across the BBMEC monolayer is measured by adding the test substance to the upper chamber and sampling from the lower chamber. The tightness of the monolayer is also characterized by the transendothelial electrical resistance (TEER). Courtesy of T. Abbruscato.

A thermochemical method that simultaneously measures differences in heat flow into a test substance and a reference substance (whose thermochemical properties are already well characterized) as both are subjected to programmed temperature ramping of the otherwise thermally isolated sample holder. The advantage of differential scanning calorimetry is a kinetic technique that allows one to record differences in heat absorption directly rather than measuring the total heat evolved/... 

While there is no standard assay design for teratogenicity or developmental toxicity screening, there are many similarities in the types of assays that have been described in the literature (4-9, 22-25). One version of these (4) is described here, and an overview of the assay design is shown in Fig. 3. Variations on this assay (alone or in combination with other techniques) can also be used for more descriptive characterization of the effects of a test substance or evaluation of the mechanisms of developmental toxicity. 

Forty-two laboratories were identified for inspection. Ongoing and completed studies would be examined as available. The inspections used a checkhst that was divided into two parts, one part covering laboratory operations and the other study conduct. The checklist arbitrarily placed mixing and storing of test substances in the area of laboratory operations and distribution and characterization of the substances in study conduct. 

Submission of a project under GLP may trigger an audit from EPA or FDA. Audits are time-consuming and stressful. Both EPA and FDA regulations address the effect of noncompliance with the standards. If a lab submits a study that is found to be in noncompliance, it can lead to a rejection of the study, suspension or cancellation of the permit, and a possible criminal and/or civil penalty. If a test substance characterization is found to be erroneous the consequences can be costly. 

The chemical aspects of these studies focus primarily on the chemical characterization of the test substance and/or mixture. The identity of the test chemical should be proven, and the analytical procedures used, such as gas or liquid chromatography, nuclear magnetic resonance spectrometry, or nass spectroscopy, should be available for audit. This would include the chromatograms or spectra from these analyses. It is imperative that raw data be left intact as they emerge from an instrument to maintain data integrity. Chro-natographic printouts are to remain attached and in sequence. If some data points are not used in the final report, the reason is to be documented and those not used are to remain with the stud/ file. 

PHYSICAL CHARACTERIZATION TESTS FOR DRUG SUBSTANCES USED IN LOW-DOSE FORMULATIONS... 

At later stages of drug development (before Phase I), when the test substance has been more fully characterized, the Irwin Test provides a clear over-all index of the test substance s margin of safety. Furthermore, although the test is mainly behavioral, it can give global indications of drug effects on vital functions such as respiration or intestinal motility. On the other hand, the test provides little information about effects... 

These assays are generally performed by applying a test substance to well characterized cell systems (e.g. bacterial or mammalian cell cultures) and evaluating changes in the growth and characteristics of the cells. This may involve assessing the speed with which colonies form and the size of the colonies as well as... 

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