Oxytetracycline efficacy and preliminary establishment of pharmacokinetic residues in tropical fish, Catla catla (Hamilton, 1822)

Abstract

Oxytetracycline (OTC) is often used in fish farms as an antibacterial agent to prevent disease outbreaks. Indiscriminate use of antimicrobials is common since many stakeholders are not aware of their potency, public health issues, and residual elimination profile in the tropical environment. The present pilot study evaluated the efficacy of oral oxytetracycline dihydrate (OTCD) at doses including 10, 55, and 82 mg/kg body weight (B·W.) in Catla catla against a pathogenic Aeromonas hydrophila. The initial efficacy study revealed that an oral dose of 55 mg OTCD/kg B.W. recorded the highest relative survival percentage (63.15%) and was selected for the final residual profile and pharmacokinetics (P.K.) study. After 10 days of medication at 55 mg OTCD/kg B.W, fish sampling was carried out at 1, 6, 11, 21, and 31 days and OTCD was determined using reverse phase-high performance liquid chromatography (RP-HPLC). The highest residue concentration (Cmax) of OTC in the tissues was ∼0.1 μg/g at 16 h (1st day). The elimination half-life (t1/2) was observed highest for muscle (10.03 days), followed by the kidney (4.57 days), and serum (4.33 days). On 11th day, the OTC level did not exceed the maximum residue level (MRL) of 0.1 μg/g. However, the residue was not detected on the 31st day in all the samples and these were considered safe for consumption.