Development of a method to determine oxytetracycline concentrations in 
water for dose verification during pivotal efficacy trials for immersion therapy

Immersion therapy with OTC-HCl may be an effective means of treating 
certain systemic fish diseases, especially of fish species that are reared on 
feed that cannot be medicated or fish that go off feed during a disease 
outbreak.  One criterion to gain a New Animal Drug Application for OTC-HCl 
immersion therapy is valid efficacy data.  An analytical method for OTC-HCl 
in immersion water that is acceptable to the U.S. Food and Drug 
Administration is needed for verification of dose during pivotal efficacy trials 
before pivotal efficacy data can be accepted.  The draft label claim for OTC-
HCl immersion therapy proposed a daily treatment of 10 to 20 mg/L as an 
immersion bath for 1 to 4 hours with daily treatments lasting from 1 to 10 
consecutive days.  To ensure the method will be adequate for the final label 
claim, a high pressure liquid chromatography method will be developed and 
validated over a range that covers the requirements for a claim of 2x the 
largest dose on the proposed label claim (20 mg/L x 2 = 40 mg/L).
Validation of the method will include a minimum analytical range of 0.5x the 
smallest dose on the label claim (10 mg/L x 0.5 = 5 mg/L) to 1.5x the largest 
possible dose on the label claim (40 mg/L x 1.5 = 60 mg/L).