DETERMINATION OF LEACHING RATE OF FLORFENICOL FROM INCORPORATED AND TOP-COATED MEDICATED FISH FEEDS VIA HPLC

Florfenicol (FFC; available commercially as AQUAFLOR® [a Type A medicated premix]) is an antibiotic approved by the U.S. Food and Drug Administration for use to control mortality associated with certain diseases in fish reared in U.S. aquaculture.  Florfenicol is administered orally as a medicated feed.  The two methods used for manufacturing FFC-medicated feed are incorporation of the medicated premix into the feed prior to pelleting or extrusion or top-coating non-medicated feed with the medicated premix at the feed mill.  Incorporation allows the antibiotic to be mixed into the feed mash before extrusion or pelleting.  Top-coating uses an animal or vegetable oil carrier to infuse the antibiotic into the feed after pelleting.  Although the two methods are frequently used interchangeably and with similar efficacy, the leaching rate of FFC may differ substantially depending on the method of incorporation.  The present study was conducted to determine the leaching rate of FFC from incorporated and top-coated medicated feeds.

Incorporated and top-coated medicated feed (6 g) were separately placed in glass jars containing 15 L of reconstituted hard water at 12°C, 19°C, and 27°C.  Feed samples were removed after 0, 1, 5, 15, 30 and 60 min immersion.  Feed samples were dried in an oven (40°C) overnight, ground into a powder and extracted with 50:50 18MΩ water/HPLC grade acetonitrile.  Extracted samples were sonicated, placed on a shaker and filtered with Envi-Carb SPE cartridges.  FFC concentrations of filtered samples were determined via HPLC with UV detection.

First-order kinetics was used to determine the half-life for FFC leaching from three different types of medicated feeds, incorporated and top-coated at three different temperatures. The half-lives for top-coated medicated feeds were 2-3 times shorter than incorporated medicated feeds.  The results indicate that the two methods of manufacturing Aquaflor-medicated feeds (incorporated and top-coated) will yield FFC-medicated feeds with significantly different leaching rates.