Buparvaquone tissue residue study

Summary

Bovine anaemia caused by Theileria orientalis is a tick borne disease and is widespread throughout Australia. However despite the widespread distribution, losses were most unusual even though parasitaemias of up to 20% and occasionally higher were seen. Since 2006, NSW Department of Primary Industries (DPI) Veterinary Laboratories have received an increasing number of submissions where Bovine anaemia caused by Theileria orientalis was diagnosed.
There is no remedy registered for use against Bovine Anaemia in Australia. Veterinarians who have treated cattle with remedies registered for other uses in Australia report variable outcomes. To-date controls have not been included so it is not possible to determine with certainty the effectiveness of treatments. Based on literature searches, buparvaquone (BPQ) is expected to be a highly effective chemotherapeutic which is supported by efficacy studies (MLA project B.AHE.0048). Manufacturers have indicated that the projected size of the market does not warrant the costs associated with registration of BPQ in Australia. It has been suggested veterinarians could apply to the Australian Pesticides and Veterinary Medicines Authority (APVMA) for consent to import an unregistered veterinary chemical product. If a permit was granted, the veterinarian would accept responsibility for residue violations. As the major overseas markets have not established a Maximum Residue Level (MRL), detection of any BPQ or metabolites would be regarded as a violation and have serious ramifications for the veterinarian and for the Australian cattle industry. A withholding period of 42 days was recommended by manufacturers of BPQ sold in overseas markets based on methodologies available in the late 1970s. Technological advances can be expected to have lowered detection limits since then.
This project involved conducting a tissue residue depletion study. Cattle in store condition were treated with BPQ 2 times 48 hours apart at the recommended dose (2.5mg/kg high up on the neck with a maximum of 10mL per injection site). Seventy-two cattle were treated which allowed for 12 sampling times with six animals sampled at each time. The animals were housed outdoors before and after treatment in accordance with normal agricultural practice. Two untreated control cattle were also included. Animals were managed in accordance with the Animal Research Authority.
Tissues (injection site neck muscle, skeletal muscle, liver, kidney, subcutaneous fat and peri-renal fat) were collected at days 7, 14, 28, 42, 56, 70, 84, 98, 119,
147, 175, and 203 after treatment. Samples were chilled following collection and placed in a freezer (-200C) within five to six hours of collection. Samples were held frozen till tested. Buparvaquone residues were determined according to the method “Determination of Buparvaquone Residues in Bovine Tissues and Milk by HPLC/MS/MS” (see MLA project B.AHE.0078).
Quantifiable residues of BPQ (>0.01 mg/kg) were found in all of the supplied tissue samples collected seven days after treatment (DAT).