NADA methods

The NADA method approval process consists of three phases (1) method development by the sponsor and generation of information to establish that the method satisfies acceptability criteria (2) FDA review of the sponsor s data to determine suitability of the method and (3) the method trial , an inter-laboratory study, which determine whether the method meets performance criteria when used in multiple laboratories. The inter-laboratory method trial procedure provides an indication of a method s ability to be used as a practicable and reliable regulatory tool. Sponsors are urged to develop methods that are mgged and exceed rather than meet the minimal standards of acceptability. Those methods that appear marginally acceptable after review often do not pass the inter-laboratory method trial. 

NADA methods should be capable of reliably measuring an analyte (i.e., the marker residue) that has a defined quantifative relationship to the total residues of toxicological concern in the tissues of interest, namely the target tissue and muscle. The target tissue is generally the last tissue in which total residues deplete to the permitted maximum safe concentration. When the marker residue is at the tolerance, a defined unique concentration, the total residues have depleted to the respectively established safe concentrations in the target tissue and muscle. 

The non-NADA method trial process mirrors the NADA process. Methods are developed, reviewed for scientific and technical soundness, and validated in multiple laboratories, and the data generated are analyzed to determine if the method is suitable for its intended use. 

The method trial process for NADA methods is different to the process for non-NADA methods. However, the validation protocol followed by the participating laboratories and the requirements for acceptance of the method are the same. The trial process also differs for determinative procedures and confirmatory procedures. Determinative procedures are evaluated using the multiple laboratory process, whereas the confirmatory method needs to be evaluated only in a single government laboratory. 

The FDA coordinates the method trial process for non-NADA methods. The sample requirements are the same as for the NADA trials. Non-Federal laboratories such as contract laboratories and State laboratories can participate in the process. For a single-residue method, the minimum numbers of samples and laboratories are the same as for NADA method trials. 

Non-NADA methods may be designed to detect multiple residues and they may be designed for use in multiple species. In order to validate these multi-residue methods, modifications to the validation protocol relative to single analyte methods are made. Additional laboratories will participate in the method trial, but the number of samples... 

Guidelines for acceptability of NADA and non-NADA methods are the same. For the determinative procedure, the criteria described in Method Criteria for accuracy and precision are used to evaluate data generated at participating laboratories. There are no criteria for accuracy in the analysis of the incurred residue samples however, the overall data set is reviewed to see if there is general agreement between results obtained by contract laboratories and relative to the levels reported in the sponsor s laboratory. 

The evaluation of all NADA analytical methods was previously conducted exclusively by the CVM. Since 1995, the CVM has offered sponsors of NADA residue methods the option of conducting the method trial through a Sponsor Monitored Method Trial (SMMT) process. The SMMT is conducted according to CVM specifications with CVM oversight. The resultant performance data must be reviewed and judged acceptable by CVM before the method is approved. 

The incorporation of screening or rapid tests into the NADA process for the purpose of regulatory application will routinely require that a rigorous confirmatory method be part of the analytical system. The requirement for a confirmatory method is part of FDA s Center for Veterinary Medicine policy for all analytical methods submitted for NADA regulatory purposes. 

Very little is known about the biosynthesis of the three most recently proposed endocannabinoids, 2-AGE, virodhamine and NADA. Regarding 2-AGE (noladin ether), this compound was previously identified in pig brain (Hanus et al. 2001) and in some rat tissues and brain areas (Fezza et al. 2002) by using mass-spectrometric (MS) methods coupled to chromatographic separations. However, a recent study cast some doubt on the actual existence of 2-AGE in mammalian brain tissue (Oka et al. 2003). At the time of this study it was already known that (1) the only acyl ethers to have been detected in animals before the discovery of 2-AGE were 2-acyl ethers (e.g. alkenyl ethers such as platelet activating factor and plasmalogens) (2) there was no evidence for the existence of any enzyme catalysing the formation... 

The relatively few QM studies of these materials reflect both the structural complexity (including low symmetry) and also the strong scattering associated with the oxygen potential, which makes the generation of reliable and efficient pseudopotentials for PW-LDA calculations difficult. There has been a concerted effort to solve this problem over the last few years which has yielded a new family of ultra-soft pseudopotentials with which oxygen has been described with plane wave cut-offs as low as 500 eV (Vanderbilt, 1990). In the all electron LCAO-HF method the major approximation is associated with the choice of basis set. This has been studied in some detail and reliable basis sets developed (Nada et al., 1990). In the absence of analytic forces, the use of this method to optimize fully the geometry of such complex structures is rare. 

Martinez-Barrera, G., Lopez, H., Castano, V. M., Rodriguez, R., Studies on the rubber phase stability in gamma irradiated polystyrene-SBR blends by using FT-IR and Raman spectroscopy. Radiation Physics and Chemistry 2004,69,155-162. Abou Zeid, M. M., Rabie, S. T., Nada, A. A., Khalil, A. M., Hilal, R. H., Effect of gamma irradiation on ethylene propylene diene terpolymer rubber composites. Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 2008,266,111-116. 

Nada, T., Terazima, M. A novel method for study of protein folding kinetics by monitoring diffusion coefficient in time domain. Biophys. J. 85, 1876-1881 (2003)... 

Nada, N., Iwahashi, H., and Umemori, F. (1994). Test result of the intermittent chlorine injection method in Jeddah 1 plant. Desalination 96, 283. 

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