Drug Research Information Bulletin - Comparison of Potential Oxytetracycline Hydrochloride Immersion-Marking Solutions And Their Effect on Water Acidification

Oxytetracycline hydrochloride (OTC) water soluble powder is approved in the U.S. for use in the skeletal marking of finfish fry and fingerlings by immersion at dosages of 200 - 700 mg/L active OTC for 2 - 6 h. The three approved OTC products distributed in the U.S. for finfish are Oxytetracycline HCl Soluble Powder - 343 (75.6% active OTC; Phoenix Scientific, Inc., St. Joseph, MO 64503; ANADA 200-247); Terramycin-343 (75.6% active OTC; Pfizer, Inc., New York, NY 10017;NADA 008-622); and TETROXY® Aquatic Soluble Powder (36.6% active OTC; Cross Vetpharm Group Ltd., Dublin, Ireland; ANADA 200-460). As OTC is an acidic compound, it must be buffered to prevent or minimize mortality in treated fish due to low pH. Methods for using anhydrous sodium phosphate dibasic as a buffer have been well-documented and recommended (Fielder 2002; Carty et al. 2007).