Abstract
Oxytetracycline, a tetracycline antibiotic,1 is one of three antibiotics FDA-approved for use in fish aquaculture2. However, there are few bath pharmacokinetic studies for its use in fish.3,4 The objective of this study is to provide data-driven recommendations for the use of oxytetracycline as a bath therapy in the giant danio (Devario aequipinnatus), as well as evaluate how varying calcium levels in the water affect the bioavailability of the antibiotic. We hypothesize that a target plasma concentration above MIC (1 mg/mL)5 is attainable but that maximum plasma concentration (Cmax) will decrease as water calcium concentration increases.3 Oxytetracycline was administered via a 12-hour bath at a concentration of 400 mg/L. Buffering with NaHCO3 was required to maintain a pH between 7.5 and 8.0. Three water calcium levels were tested: 5.1 mg/L, 11.2 mg/L, and 60.0 mg/L. Fish were euthanized for blood and tissue sampling from 0 to 36 hours after being removed from the treatment bath. The observed Cmax (1.31 mg/mL) was well above the goal MIC at the 5.1 mg/L calcium level, but at higher calcium levels Cmax decreased to 0.78 mg/ml and 0.60 mg/ml, respectively. The calculated half-life of excretion in each treatment group was 13.21 h, 14.19 h, and 14.99 h. The two-compartment model fitted with the observed data. From these results, daily oxytetracycline baths at 400 mg/L with water calcium levels of 5.1 mg/L or less will optimize efficacy.
Acknowledgements
The authors would like to thank the University of Florida for providing the funding and support for this research.
* Presenting author
+ Student presenter
Literature Cited
1. Plumb DC. 2015. Plumb’s Veterinary Drug Handbook. 8th ed. Ames, IA: Wiley-Blackwell; 802–806.
2. Approved Aquaculture Drugs. US Food and Drug Administration. https://www.fda.gov/AnimalVeterinary/DevelopmentApprovalProcess/Aquaculture/ucm132954.htm. Accessed Nov 17, 2017.
3. Noga EJ. 2010. Fish Disease: Diagnosis and Treatment. 2nd ed. Ames, IA: Wiley-Blackwell; 382–383.
4. Rigos G, Nengas I, Alexis M. 2006. Oxytetracycline (OTC) uptake following bath treatment in gilthead sea bream (Sparus aurata). Aquaculture. 261:1151–1155.
5. Miller RA, Reimschuessel R. 2006. Epidemiologic cutoff values for antimicrobial agents against Aeromonas salmonicida isolates determined by frequency distributions of minimal inhibitory concentration and diameter of zone of inhibition data. AJVR. 67:1837–1843.