PMF 5316 A-000 & C-0001

Arthur L. Craigmill, Ph.D.
IR-4 Animal Drug Coordinator
Western Region
Environmental Toxicology
University of California
Davis, California 95616

Dear Dr. Craigmill:

We refer to your submissions dated June 28, 1990, and November 17, 1992, concerning the public master file (PMF) 5316 for the use of oxytetracycline LA-200® (OTC) in goats for the treatment of bacterial pneumonia caused by Pasteurella spp. The June 28, 1990, submission (A-000) contained information on efficacy, target animal safety, tissue residue depletion, environmental assessment, FOI summary, and proposed label. It also contained an authorization from Pfizer allowing CVM to refer to their NADA 113-232 on behalf of this PMF. The November 17, 1992, submission contained additional information requested in a telephone conference between CVM representatives and Dr. John Babish on September 24, 1992, concerning methodology for the determination of OTC in animal tissues.

We have completed our review of the submissions and have the following comments.

EFFICACY

We are unable to complete our review of the pharmacokinetic study results of OTC in goats until the following questions pertaining to the microbiological method validation information are provided.

1. You should address the following pertaining to the large plate procedure.

a. How was the uniformity of the depth of the media verified?
b. What length of time was required to run a complete assay (fill all required wells)?
c. How was the large plate positioned in the incubator?
d How the dish was sealed?

2. A step-by-step example should be provided which demonstrates how data is generated starting from the zone of inhibition value, to standard response lines, to sample potency, to residue value. Dilution Factors should be stated. You should specifically describe how you constructed your standard response lines. We prefer that standard response lines be generated using a log transformation, straight-line method with a least squares fitting procedure, and a test for linearity as described in USP XXII, <111> Design and Analysis of Biological Assays.

3. The large plate method provided states that a "100 cm X 100 cm" plate was used for the proposed method. Since this size plate does not exist, you should clarify what size plate was used for the method. You should also describe how samples are applied to the plate (plating pattern(s)).

4. We have the following concerns regarding the recovery data provided on pages 233 - 236 of the A000 submission. Currently, it is our policy that if the designated concentration of marker residue (Rm) is 0.1 ppm or greater, an average recovery of 80 to 110% should be obtained. We note that the recoveries stated on pages 233 - 236 do not fall within acceptable ranges. You should describe how the percent recovery values were calculated and comment on the variation observed in the % recovery (For example, we note that a percent recovery of 202.8 percent is stated for goat liver spiked at 2.0 ppm and 70 percent recovery was obtained for goat kidney spiked at 0.1 ppm).

5. You state that the limit of detection is .01 ppm for oxytetracycline diluted in buffer and the sensitivity in tissue is "less than 0.1 ppm" (stated on page 199 of the A-000 submission) in tissues. You should provide data to show how you determined that the sensitivity in tissue. Be advised, the limit of quantitation as defined in the greenbook is determined by multiplying the sensitivity by the dilution factor, and factoring by recoveries, if necessary, for each tissue type (muscle, fat, liver, and kidney).

6. You should state the lowest acceptable zone of inhibition reading.

7. We were unable to locate interference data to show that there is no background activity associated with the control tissue. All available data should be provided to show there is no interference associated with the new matrix.

TARGET ANIMAL SAFETY

The target animal safety study is acceptable. The results of the study demonstrate that except for local tissue irritation at the site of injection, the drug (LA-200®) is safe and well tolerated by goats at three times the recommended dose and repeated once after three days.

Because of tissue irritation with this drug, there is concern for the esthetic aspect of the injection site following drug administration. If the injection site has not resolved to a point where the consumer cannot detect discoloration or an area of demarcation by the withdrawal time presented on the labeling, a trim out statement will be required. This statement may specify the time when the injection sites are esthetically suitable for the consumer. In order to determine when the injection sites are esthetically sound, we usually recommend wet photography and critical evaluation of the injection sites at various time intervals. If you need assistance in designing such a study, please contact us.

TISSUE RESIDUE DEPLETION

The tissue residue depletion study is provisionally accepted pending successful resolution of the microbiological method validation issues identified above.

Your study appears to have been generally well conducted.

We note that the individual weight data for the goats is not included with the submission. Your Abstract states that two animals served as controls. This does not agree with the body of the report or the total number of goats used (21). Inclusion of the individual animal data would clarify both the number of animals used in the study, their assignment to slaughter groups and, given weights and administered doses, assure that the study was conducted at the 9 mg/lb (≈20 mg/kg) dosing rate.

On the basis of the tissue residue results, we conclude that additional slaughter points earlier in the study would have been helpful. None of the tissues contain consistently measurable residues in all slaughter animals for three time points. The lack of a smooth decline in tissue depletion contributes to the size of the confidence interval computed by our residue depletion model.

We have applied our statistical model to compute a withdrawal period for the use of Liquamycin LA-200® in goats. The model uses a 99% tolerance limit approach with 95% confidence. For the calculation, we have assigned the tolerance for OTC in tissues of cattle, established under 21 CFR 556.500(c), 0.1 ppm (100 ppb), to OTC residues in goats. Only those tissue concentrations above the limit of detection were used in the calculation. Using our model, we compute the following withdrawal periods for goat tissues:

Kidney   26 days

Muscle   57 days

The model algorithm does not converge for fat, liver or injection site.

The following additional data evaluation were conducted:

1. A single additional 100 ppb point at 14 days was added and the withdrawal period was recalculated. With this additional residue point, we compute the following withdrawal periods:

Kidney   35 days

Liver   32 days

2. Using the tolerance of 100 ppb for a mean value and a standard deviation similar to that seen at 4 and 7 days postdosing, residue points were generated for the 14-day slaughter point. These residues are more conservative than the data submitted by you, since mean value at 14 days is computed to be 100 ppb rather than zero. Adding this additional data to the statistical model, we compute the following withdrawal periods:

Kidney   26 days

Liver   33 days

With the exception of the withdrawal period calculated using the residue data for kidney, without additional data manipulation, all withdrawal times for edible tissues calculated using the statistical tolerance method exceed those proposed in the current submission. Application of our 99% tolerance limit approach to data that does not include three well-quantified slaughter points and where residue concentrations are highly variable, almost certainly explains the lack of algorithm convergence and the long withdrawal periods calculated. On the basis of our calculation, residues of OTC in goat kidney deplete to less than 0.1 ppm by 35 days (5 weeks) postdosing under the conditions of this study.

ENVIRONMENTAL IMPACT ASSESSMENT (EIA)

The EIA provides sufficient information for us to determine that use of injectable OTC LA-200® in goats is not expected to have a significant impact on the environment.

When an NADA for the proposed use is submitted, it will be necessary for the sponsor to provide information concerning the potential environmental impacts of the manufacturing process. Specifically, for any domestic manufacturing site(s), the sponsor should submit a) a list of substances expected to be emitted; b) the emission controls exercised ; c) a citation of and signed statement of compliance with applicable emissions requirements (including occupational) at the Federal, state and local level; and d) a discussion of the effect the approval have upon compliance with current emission requirements. The information provided concerning the occupational effects should include a copy of the material safety data sheet (MSDS) for OTC LA-200®.

The same information must be provided for any foreign manufacturer. Alternatively, the sponsor can provide a letter from the foreign government official responsible for assuring compliance with the laws of the country where manufacturing is occurring, stating that manufacturing facility is in compliance with the environmental requirements of the country.

The manufacturing environmental information will be evaluated along with the information provided in the Veterinary Master File EIA and, if appropriate, a finding of no significant impact (FONSI) will be prepared for the approval of the NADA.

FOI SUMMARY

We defer comments on the FOI summary until the above microbiological method validation issues are resolved.

LABELING

The proposed draft labeling submitted is acceptable. However, when an NADA for the proposed use is submitted, it will be necessary for the sponsor to submit the facsimile labeling with the approved withdrawal period.

Future correspondence regarding these submissions to the file for your PMF should be identified by the date of this correspondence and our file numbers, PMF 5321 A-000 & C-0001, and be addressed to the Document Control Unit, HFV-199. Please include only one request per submission, clearly stating the request in the first paragraph of the submission.

If you have questions regarding this correspondence, please contact Dr. George Haibel, Chief, Antimicrobial Drugs Branch at 301-594-1644.

Sincerely yours,

/s/
Steven D. Vaughn, D.V.M.
Director, Division of Therapeutic
Drugs for Food Animals
Office of New Animal Drug Evaluation
Center for Veterinary Medicine