Evaluating Flushing Procedures to Prevent Nicarbazin Carryover during Medicated Feed Manufacturing

Carryover of medicated feed additives between batches of feed can potentially result in harmful drug residues in the edible tissues of food-animals. The US Federal Drug Administration's (FDA) Current Good Manufacturing Practices (CGMP) regulations require medicated feed manufacturers to use one or more of the approved cleanout procedure. Flushing the equipment with an ingredient, such as ground grain, is one method used to remove any residual medicated feed from the system. It is generally recommended that the quantity of flush used be between 5 and 10% of the mixer's capacity. However, there is little data that supports this recommendation. Therefore, an experiment was conducted to determine the minimum quantity of flush material required to prevent drug carryover; and to quantify the interrelationship between flush size and drug concentration.

This case study was conducted in the Feed Processing Research Center in the Department of Grain Science & Industry at Kansas State University. Five flush size treatments were evaluated using the same nicarbazin level (125 mg/kg): 2.5, 5.0, 10, 15, and 20% of the mixer's total capacity. The feed medicated with nicarbazin was manufactured and conveyed from the mixer (454.5 kg), through a drag conveyor (3.79 kg/s) and bucket elevator (19.96 MT/h), and into a finished product bin (5.44 MT). The system was then flushed using ground corn in the amount of the five flush size treatments. Subsequently, a non-medicated diet was conveyed through the system and samples were collected and analyzed for nicarbazin.

No significant (P > 0.05) differences were detected among the flush treatments, and all treatments were effective in preventing nicarbazin carryover to the non-medicated diet. Regarding which manufacturing equipment was the major source of nicarbazin carryover, our data pointed towards the bucket elevator and finished product bin. Of these two, the finished product was considered the major source of nicarbazin carryover in our system having three treatments (treatment 2, 3, and 4) out of the five with the highest detectable drug residues.

The results of this case study emphasized the interrelationship between the flush size and the level of nicarbazin carryover throughout a feed manufacturing system. Data collected agreed with the FDA's recommendation of using 5 to 10% of the mixer's total capacity as the flushing material. Even though a 10% flush removed more drug residue (5.45x10⁴ mg) from our system compared to the 5% flush (3.36x104 mg), treatments did not differ significantly (P < 0.005). Therefore, a 5 % flush size is as effective yet less expensive.

¹Food and Drug Administration, Department of Health and Human Services. 1976. Current Good Manufacturing Practice for Medicated Feeds. 21CFR part 225.65. Fed. Regist. 41:52618.