1a. Objectives (from AD-416):
The objective of this research is to provide pork producers with practical treatment and withdrawal guidelines for the use of penicillin G procaine in sows. The research will supply a mechanism for pork producers and veterinarians to provide therapeutic intervention with penicillin G procaine in sows without the risk of carcass condemnation after slaughter due to violative residue levels. The research will also provide guidelines to USDA-FSIS on the practical limitations on the use of the newly adopted Charm-KIS microbial inhibition test when detecting penicillin residues in swine tissues. In addition, the research will determine the usefulness of the Charm-KIS test with plasma and urine samples obtained from test animals. These matrices might serve as useful surrogates for tissues in determining penicillin residues in live animals. Testing of urine or plasma might mitigate risks to producers who have dosed penicillin G procaine using dosing regimens not covered by specific residue depletion studies. Specifically, the research should provide: • Guidelines on appropriate patterns of intramuscular delivery of penicillin G procaine to sows. • Appropriate withdrawal periods for sows treated with penicillin G procaine under treatment conditions typically recommended by veterinarians. • The incidence of "false-positives" and "false-violative" returned by the "Charm-KIS" test under controlled conditions. • The usefulness of matrices other than kidney or muscle to assess whether penicillin G procaine residues have depleted from edible tissues.
1b. Approach (from AD-416):
Non-medicated sows (n=80 per trial; >182 kg; total 2 trials) will be purchased from a commercial hog farm and housed indoors in a controlled environment. Three treatments will be used (10 ml single injection, 20 ml multiple injection and 20 ml multiple injection). Treatments administered to sows will be at five-times the dosage of penicillin G procaine normally administered to hogs on each of 3 consecutive days. Three animals from each treatment will be sacrificed at withdrawal day 5, 10, 15, 20, 25, 32, 40 and tissues (kidney, skeletal muscle, adipose tissue) and body fluids (urine and blood) collected for analysis. The penicillin residues will be determined by the Charm-KIS system. Penicillin residues in KIS-positive and KIS-negative kidney and muscle will be confirmed and quantified using a combination of LC-MS/MS methods described by the USDA-FSIS (CLG-BLAC.03, “Screening and confirmation of ß-lactam antibiotics by HPLC-MS/MS). The usefulness of the matrices other than kidney and skeletal muscle for determining the depletion of penicillin G procaine residues from edible tissues will be evaluated.
3. Progress Report:
A study was conducted to determine the depletion of penicillin G procaine residues from tissues of heavy sows treated with a 5x dose for three consecutive days. In one portion of the study, penicillin residues were measured in kidney and skeletal muscle using the rapid screening test employed by Food Safety and Inspection Service veterinarians within slaughter plants. The objective of the study was to determine the reliability of the tests and the length of time required for tissues to consistently test negative using the regulatory screen. Positive and negative results obtained from the rapid screening assays are currently being confirmed or refuted using a sensitive and very specific mass-spectrometry based method. The study will provide the incidence of false positive and false negative results returned by the rapid screening assay and will provide data on which to base a withdrawal period for swine treated with penicillin G procaine in an extra-label manner.