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U.S. Department of Health and Human Services

Animal & Veterinary

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by Mary G. Leadbetter
FDA Veterinarian Newsletter March/April 1999 Volume XIV, No II

The following information was presented at the 112th AOAC International Annual Meeting and Exposition, Montreal, Quebec, Canada, on September 13, 1998.

The Center for Veterinary Medicine (CVM) requires appropriate analytical test methods be provided as part of a New Animal Drug Application (NADA) for the approval of a Type A Medicated Article. The regulations covering medicated articles and feeds are provided in 21 CFR 558, NEW ANIMAL DRUGS FOR USE IN ANIMAL FEEDS, and the GMP regulations are provided in 21 CFR 225 for MEDICATED FEEDS and 21 CFR 226 for TYPE A MEDICATED ARTICLES. The test methods to determine the concentration of the active ingredient in Type A Medicated Articles and Type C Medicated feeds are critical control procedures. These critical control test procedures are evaluated for completeness in written description, practicality and appropriateness. These methods are provided in Standard Operating Procedure (SOP) formats, which are more detailed than published procedures. The performance of the method must be supported by validation information that demonstrates the method can meet the appropriate criteria for recovery, precision, accuracy, linearity and specificity.

The sponsor releases the Type A Medicated Articles based on release specifications. Release specifications are needed to assess whether the product’s concentration or potency is within approved specified limits. The sponsor retains control and responsibility for the quality and accuracy of the results obtained from their testing facilities. However, Type C Medicated feeds are usually produced by feed mills from Type A Articles and are not routinely assayed before use. Some sponsors maintain Customer Service Laboratories, that will provide an analysis of medicated feeds. State feed laboratories assay medicated feed samples to check for agreement with the labeled concentration. Independent contract laboratories will also assay feed samples for customers.

Prior to approving new feed methods, CVM requires the sponsor to conduct additional testing of Type C Medicated feed methods because these test methods are used by testing laboratories not under the control of the sponsor. The analysts perform the analysis using the available test methods. In order to have well tested and validated medicated feed assay methods available, many Type C Medicated feed methods for new approvals undergo multi-laboratory evaluation to assure the practicality, transferability and performance of the method. This process is called a "method trial." At least three participating laboratories are needed, and include both contract and state feed laboratories. The method trial process assures that the instructions provided in the test method include sufficient detail so that a competent analyst can adequately perform the procedure based on the information provided in the method alone. The multi-laboratory evaluation is done to assure the transferability of the Type C Medicated feed methods. The evaluation of new alternate Type C Medicated feed methods for existing approved products requires similar information. However, the demonstration of transferability of new up-to-date test methods does not require a multi-laboratory evaluation. A one laboratory evaluation by an independent contract laboratory is sufficient. These methods are not considered confidential information and can be obtained from CVM. Alternately, the sponsor can choose to conduct an AOAC collaborative study.

A method validation report is submitted to CVM to begin the method evaluation process. The report provides a proposed detailed method description and the data to demonstrate the performance of the method. The evaluation criteria for Type C Medicated feed methods are the same whether the methods are submitted for an original approval or as new methods for existing approved Type A Medicated Articles. The evaluation criteria for the validation of the method are outlined below:

  • Linear standard curve. Single point calibration techniques are acceptable only if the calibration curve is linear with an intercept close to zero.
  • Recovery (Average). Eighty (80) to 110 percent of Labeled Concentration. The assay is tested at 50 percent of the lowest proposed concentration. Correction factors are usually unacceptable.
  • Within Laboratory Coefficient of Variation. The results for replicate analysis, usually 5, feed matrix samples fortified at 1/2 and 1 times the lowest labeled concentration, and 1 and 2 times the highest labeled concentration. The results should give a Coefficient of Variation as a percent no greater that 5.0 percent for concentrations 10 ppm or greater, and no greater than 7.5 percent for concentrations less than 10 ppm.
  • Background Interferences. Control feed matrix samples should have interferences equivalent to less than 10 percent of the lowest labeled concentration.
  • Specificity. The effect (or non effect) of selected potential interfering substances. The response for the active ingredient should be clearly resolved from any other responses potentially present and should be readily distinguishable above the background signal.
  • Proof of Recovery from Medicated Feed Samples. The recovery of the active ingredient from control feed matrix may not adequately reflect the performance of the method with medicated feed manufactured in commercial size mixers. The efficient isolation of the active ingredient from finished medicated feed samples should be demonstrated. Data are needed for the analysis of at least two commercial size batches; ideally one produced in a horizontal mixer and one produced in a vertical mixer. The batch size should be at least one-thousand pounds.
  • Number of Samples per Day. Feed Laboratories have limited resources and a large workload. A reliable method that can process at least 7 to 10 individual samples in a day is desired.
  • Ruggedness. The method should be rugged enough for routine use by reasonably experienced analysts. The method should not include a large number of critical steps. The number of individual operations necessary should be considered during method development, with all critical steps clearly identified.
  • Practicality. The method should use the most common and reliable equipment, reagents, and materials. Unique or research instrumentation, large quantities of solvents, reagents, and supplies may render the method economically impractical for State Feed Laboratories.
  • User Safety and Waste Disposal. The method should be developed with a consideration of worker safety and the disposal of hazardous chemicals. Chlorinated solvents should be avoided.

The current method trial process for new approvals consists of four stages. The first stage is the review and acceptance by the CVM of the method description and supporting performance data, and of the draft protocol for the laboratory evaluation. The second stage is the method demonstration at the laboratory designated by the sponsor. During the second stage, the method description and protocols for the laboratory evaluation are revised to address the observations and/or comments from participants. The third stage is an inter-laboratory testing of the method in each of the multiple participating laboratories. During the third stage, we request the sponsor to analyze the same sample set as analyzed by the participants. The fourth stage is the documentation of the trial. The documentation includes the submission of summary report prepared by the sponsor to which copies of the individual laboratory reports are attached. The report for the set of samples analyzed by the sponsor’s laboratory is included. If the data show the method can meet CVM performance criteria, the method is approved after the method description is evaluated and revised as needed based on the observations and comments of the participating analysts.

Many Type A Medicated Articles that were approved years ago no longer have test methods that can meet current standards. These methods often do not have adequate specificity and do not give an accurate estimation of the concentration of the active ingredient in the medicated matrix. For Type A Medicated Articles, the sponsor can submit and get approval for a more up-to-date test method by submitting a supplemental application for the test method. The test method must be in an SOP format supported by appropriate validation data, and include a bridging study to show the proposed test method performs as well or better than the approved test method. However, for Type C Medicated feed methods, additional supporting information is necessary. The transferability of the method must be demonstrated. Sponsors do not want to submit new up-to-date methods and also be required to undertake a multi-laboratory method trial. In addition, the sponsors are concerned about the possibility of having their current Type C Medicated feed assay limits as provided in 21 CFR 558.4 (d) re-evaluated.

Currently, we have two sponsors who have submitted new up-to-date Type C Medicated feed methods for existing products. Before the new methods were submitted, the sponsors contacted CVM’s Division of Manufacturing Technologies to discuss the approval requirements. The sponsors were concerned about the cost of a multi-laboratory evaluation and that CVM would re-evaluate the assay limits. However, CVM agreed not to re-evaluate the assay limits and to modify the requirements for transferability. These sponsors agreed to our proposal for a modified test of the transferability of the method. The method and supporting data would be evaluated for adequacy according to the criteria and procedure currently used in our method trial procedure. This is the same as stage 1 of the current method trial process. However, a multi-laboratory method trial would not be conducted. A one laboratory evaluation by an independent contract laboratory would be conducted by the sponsor with CVM’s agreement to the protocol. This combines stages 2 and 3 of our current process into one stage. In this process, the method demonstration would be optional. The third stage is the documentation stage, similar to the current stage 4. Any improvements in the test method should be discussed in the report prepared by the sponsor. In this way, the transferability of the method could be evaluated at a more reasonable cost to the sponsor. At this time, we are working with the two sponsors to develop the supporting data required and to provide more detailed SOPs that have all the instructions and information required.

Sponsors of older approved products have other options available to gain approval of improved test methods. The sponsor could choose to conduct an AOAC collaborative study through the AOAC or a multi-laboratory CVM method trial. However, with limited resources and a decline in participation by FDA field laboratories, sponsors are reluctant to expend the time or money required. We are testing the one laboratory evaluation approach to encourage sponsors to provide better test methods for Type C Medicated feed methods.