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Doxycycline is an important medicine in aquaculture for treating fish diseases. However, its excess use causes residue exceeding to threaten human health. So, this study aimed to estimate a reliable withdrawal time (WT) of doxycycline (DC) in crayfish (Procambarus clarkii) based on statistical approaches and conduct a risk assessment for human health in the natural environment. Samples were collected at predetermined time points and determined by high-performance liquid chromatography. A novel statistical method was used to process the data of residue concentration. The homogeneity and linearity of the regressed line of data were evaluated by Bartlett's, Cochran's, and F tests. Outliers were excluded by establishing the standardized residual versus their cumulative frequency distribution on a normal probability scale. The calculated WT was 43 days in muscle of crayfish based on China and European stipulations. After 43 days, estimated daily intakes of DC were ranged from 0.022 to 0.052 µg/kg/d. Hazard Quotients were ranged from 0.007 to 0.014, which were far less than 1. These results indicated that established WT could avoid health risks for humans resulting from DC's residue in crayfish., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The objective of the present study was to investigate the pharmacokinetic (PK) properties of doxycycline (DC) in crayfish after three different drug administrations of oral (per os , P.O.) gavage, intramuscular (IM) injection, and intrasinus (IS) injection at a dose of 20 mg/kg at 24.0 °C. Samples of hepatopancreas, muscle, gill, and hemolymph were collected at pre-determined time points after cessation of drug treatment (n = 5 for per time point). DC concentrations were determined by high-performance liquid chromatography with an ultraviolet detector. Results demonstrated that the multiple-peak phenomenon occurred in hemolymph and tissues irrespective of using any drug administration. With the changing of drug administration, the PK parameters were correspondingly altered. The elimination rate constant (t 1/2λ) were 28.90, 32.99, and 31.70 h; 42.00, 60.21, and 25.28 h; 32.17, 26.00, and 21.15 h; 69.53, 23.25, and 31.20 h in hepatopancreas, muscle, gill, and hemolymph after P.O., IM, and IS dosing, respectively. The values of the area under the concentration-time curve (AUC last) after IM and IS treatment were comparable in hepatopancreas, muscle, gill, and hemolymph, respectively, but the value following P.O. treatment was less than the values after IM and IS treatment except for hepatopancreas that presented an opposite trend. The volume of distribution (V z _F) was estimated to be 2625.30 mL/kg, and the systemic total body (Cl_F) was 58.30 mL/h/kg. Finally, the P.O. and IM bioavailability were calculated to be 19.58% and 104.76%. This study will provide the useful PK information of DC after different administrations, and is beneficial for a specific dosage regime in line with the drug given route. • Doxycycline's PKs were investigated in crayfish after P.O., IM, and IS administrations. • The changing of drug administration considerably affected t 1/2λz , T max , C max , and AUC last. • Bioavailability values were 19.58% and 104.76% after oral and intramuscular dosing. • The results provide useful information for the effective use of doxycycline in crayfish. [ABSTRACT FROM AUTHOR]