liminfoFARAD Reference
Free reference guide: FARAD Reference
About FARAD Reference
The FARAD Reference is a searchable guide to the Food Animal Residue Avoidance Databank (FARAD), covering 26 essential topics for veterinarians, food safety professionals, and livestock producers. It explains the FARAD system operated by a consortium of US universities (NC State, University of Florida, Kansas State, UC Davis) and details withdrawal time (WDT) fundamentals, the difference between FDA-approved WDT and FARAD-recommended withdrawal intervals (WDI) for extra-label drug use, and the AMDUCA regulatory framework governing ELDU in food animals.
Regulatory entries cover FDA tolerance levels and Codex MRL values for common veterinary drugs (Penicillin at 5ppb in milk and 50ppb in muscle, Oxytetracycline at 2ppm in muscle), safe level requirements for drugs without established tolerances, USDA FSIS National Residue Program monitoring, screening test methods (Charm II, SNAP, Delvotest), and LC-MS/MS confirmatory analysis with 0.1-10ppb detection limits. Pharmacokinetics entries explain ADME principles, tissue residue depletion curves across muscle, liver, kidney, fat, and injection sites, and half-life-based WDT estimation.
Species-specific withdrawal entries provide actual WDT values: cattle (Penicillin G IM 10 days, Oxytetracycline IM 28 days, Ivermectin SC 35 days), swine (Tylosin IM 14 days, Ivermectin SC 18 days), poultry (strict ELDU restrictions, no egg-laying drugs), and aquaculture (temperature-dependent degree-days concept, Oxytetracycline 21 days at 21C). Special situation topics include compounded drug residue risks, topical/pour-on systemic absorption, emergency slaughter PK modeling, VFD feed directive regulations, organic livestock requirements under USDA NOP, and international trade MRL differences.
Key Features
- Withdrawal time (WDT) reference for cattle, swine, poultry, and aquaculture species with actual drug-specific day counts
- FARAD-recommended WDI (Withdrawal Interval) for extra-label drug use with extended period calculations based on PK data
- FDA tolerance and Codex MRL values for Penicillin, Oxytetracycline, Gentamicin, Ceftiofur, Flunixin, and other common veterinary drugs
- AMDUCA/ELDU regulatory framework: veterinarian-patient relationship, record keeping, prohibited substances (chloramphenicol, clenbuterol)
- Screening test methods (Charm II, SNAP, Delvotest for milk) and LC-MS/MS confirmatory analysis with 0.1-10ppb detection limits
- Pharmacokinetics (ADME) principles and tissue residue depletion ranking: injection site > kidney > liver > muscle
- Temperature-dependent aquaculture withdrawal using degree-days concept for Oxytetracycline, Florfenicol, and Sulfadimethoxine
- Special scenarios: compounded drug risks, pour-on systemic absorption (Ivermectin 48 days), emergency slaughter PK modeling, organic livestock USDA NOP rules
Frequently Asked Questions
What is FARAD and who should use this reference?
FARAD (Food Animal Residue Avoidance Databank) is a US veterinary drug residue information system operated by a consortium of universities. This reference is useful for veterinarians prescribing drugs to food animals, livestock producers managing withdrawal periods, food safety inspectors, and veterinary students learning pharmacokinetics and residue regulations.
What is the difference between WDT and WDI?
WDT (Withdrawal Time) is the FDA-approved minimum waiting period from last dose to slaughter or milking printed on the drug label. WDI (Withdrawal Interval) is a FARAD-recommended extended period for extra-label drug use, calculated from pharmacokinetic data and tissue residue studies. For example, Flunixin IV in cattle has a WDT of 4 days, but extra-label IM use requires a WDI of 30+ days.
What drugs are prohibited for extra-label use in food animals?
Under AMDUCA, certain drugs are absolutely prohibited for extra-label use in food animals, including chloramphenicol, clenbuterol, diethylstilbestrol (DES), nitroimidazoles (metronidazole, dimetridazole), nitrofurans (furazolidone), sulfonamides in lactating dairy cattle over 20 months of age, and fluoroquinolones in food-producing animals.
How are drug residues detected in food products?
Milk is tested at every tanker pickup using rapid screening tests like Charm II (beta-lactams, tetracyclines), SNAP test (Idexx), or Delvotest (broad spectrum). Tissue residues are monitored through the USDA FSIS National Residue Program with random sampling at slaughter plants. Positive screening results are confirmed by LC-MS/MS analysis at accredited laboratories with detection limits of 0.1-10 ppb.
Why are aquaculture withdrawal times temperature-dependent?
Fish are ectothermic, so their metabolism and drug elimination rates vary directly with water temperature. Cooler water slows drug clearance, requiring longer withdrawal periods. The degree-day concept accounts for this: Oxytetracycline withdrawal is 21 days at 21C but proportionally longer at lower temperatures. Only a very limited number of drugs are approved for aquaculture use.
What happens during an emergency slaughter situation?
When a treated animal requires emergency slaughter before the withdrawal period expires, veterinarians can contact FARAD (1-888-USFARAD) for a residue level estimate. FARAD uses pharmacokinetic modeling based on drug dose, route, time since administration, and species to predict tissue residue concentrations and advise whether slaughter is safe or if the carcass should be condemned.
Can antibiotics be used in organic livestock production?
Under USDA National Organic Program (NOP) rules, antibiotics are prohibited for both prevention and treatment in organic livestock. If an organic animal requires antibiotic treatment, it permanently loses its organic certification. However, refusing treatment is an animal welfare violation. Allowed interventions include vaccines, vitamins, and electrolytes. Synthetic parasiticides are also restricted.
How do international MRL differences affect livestock exports?
Countries set different MRL standards that can block trade. For example, ractopamine is permitted in the US but banned in the EU, and zilpaterol is allowed in the US but prohibited in Russia. Exporters must verify destination country regulations through USDA FSIS Export Verification programs and Codex Alimentarius international reference standards.