Location: Livestock Arthropod Pest Research Unit
Project Number: 3094-10400-001-010-I
Project Type: Interagency Reimbursable Agreement
Start Date: Aug 21, 2025
End Date: Sep 30, 2026
Objective:
1. To establish critical PK parameters and muscle tissue concentrations for each active ingredient (ivermectin and doramectin) and feeding level (two feeding (g/ton) levels per active ingredient).
2. To compare critical pharmacokinetic parameters reported in the literature in cattle treated with a single dose of 0.2 mg/kg body weight dose of ivermectin 1% and doramectin 1% to cattle fed ivermectin or doramectin Type C free-choice medicated feed blocks (molasses blocks).
3.To determine the consumption rate of the four medicated feed block formulations, two feeding levels each for ivermectin and doramectin.
4. To determine appropriate conditions of use for an ivermectin and/or doramectin Type C free-choice medicated feed block for the prevention of NWS myiasis within the USDA’s NWS eradication program.
5. To provide plasma PK, and tissue concentration data; and consumption data to inform the design of future effectiveness studies.
Approach:
The purpose of this agreement between the FDA Center for Veterinary Medicine (CVM) and USDA Agricultural Research Services (ARS) is to complete a study to determine critical PK parameters in cattle fed an ivermectin or doramectin Type C free-choice medicated feed block (molasses block). Although threshold blood and tissue concentrations that correlate with clinical effectiveness in susceptible populations of NWS larvae are not known, a comparison of the measured critical PK parameters to those established from published literature following subcutaneous injection of ivermectin 1% and doramectin 1% at the same dosage used in the prevention of infestations of NWS (myiasis), provides information that may allow FDA and USDA to make a risk-based emergency decision regarding the usefulness of these products within the USDA-APHIS screwworm eradication program. Data generated from this study should also provide information to facilitate the design of future effectiveness studies. Through this research, CVM and ARS will work collaboratively to determine if a Type C free-choice medicated block may be useful as an emergency tool to prevent the entry of and spread of NWS in the US until the sterile fly production is sufficient to eradicate NWS.