Pharmacokinetics and tissue elimination of enrofloxacin in 

Penaeus monodon after oral administration

FAN Peili1，2，WANG Yuan2，ZHAO Shu2，LI Xinshu1，

WANG Hongbin1，LING Hai2, LI Chuanbu2, FANG Wenhong2

（1. School of Marine Science and Fisheries, Jiangsu Ocean University， Lianyungang Jiangsu222005, China; 

2. Key Laboratory of East China Sea Fishery Resources Exploitation and Utilization, Ministry of Agriculture and Rural 

Affairs; East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai200090, China）

Abstract: Shrimp is extensively farmed all over the world and provides highquality animal protein in human diet. But like most other farmed aquatic animals, diseases, especially caused by bacteria, frequently break out in Penaeus monodon culture industry with the development of intensive aquaculture, and antimicrobial drugs play the most effective and direct role. Enrofloxacin (ENR) is a quinolone carboxylic acid derivative with antimicrobial action, which is bactericidal through inhibition of DNAgyrase. Enrofloxacin is effective against gramnegative and grampositive bacteria. Enrofloxacin is a special drug for animals and is widely used in the prevention and treatment of animal infectious diseases. The main metabolite of enrofloxacin in animals is ciprofloxacin, which is also allowed to be used in aquaculture in China. At present, enrofloxacin has been studied in aquatic animals such as fish, shrimp and crab, but there are species differences in drug metabolism in different animals. At present, there are only studies on the effects of enrofloxacin on the oxidative stress of hepatopancreas and gills of Penaeus monodon, but the metabolism and elimination of enrofloxacin and ciprofloxacin in vivo have not been reported. In order to guide the rational application of enrofloxacin for the prevention and control of bacterial diseases in Penaeus monodon, high performance liquid chromatography (HPLC) was used to study the pharmacokinetics and tissue distribution of enrofloxacin and its metabolite ciprofloxacin in Penaeus monodon. The dosage of enrofloxacin (30 mg·kg -1) was orally administrated to Penaeus monodon in seawater (salinity of 33) at temperature (28.0 ± 1.0) ℃. Pharmacokinetic noncompartmental modeling of drug concentrationtime data were performed using Drug and Statistics Software DAS Version 2.0. The pharmacokinetic parameters were analyzed based on statistical moment theory for the hemolymph and tissues concentrationtime data of enrofloxacin and its active metabolite ciprofloxacin. This is the first study on the pharmacokinetics and tissue disposition of enrofloxacin and its metabolite ciprofloxacin in Penaeus monodon. The concentrationtime curve of enrofloxacin in the hemolymph of Penaeus monodon was best fitted to twocompartment open model with firstorder absorption. Tmax and Cmax represented the extent of drug absorption. The former corresponded to the absorption rate, while the latter corresponded to the absorption magnitude. The peak time (Tmax) of enrofloxacin in hemolymph, muscle and hepatopancreas were 1 h, 2 h and 2 h, respectively, Cmax were 17.82 mg·L -1, 5.02 mg·kg -1 and 96.75 mg·kg -1, respectively. The AUC0-t and Vz represented the extent of drug distribution. It was generally believed that the higher the AUC value was, the more drugs penetrated into the tissue and the more widely distributed they were. The critical value was usually (0.81.0) L·kg-1: when Vz was close to (0.81.0) L·kg-1, it indicated that the drug was widely and evenly distributed in vivo. When Vz was greater than 1 L·kg-1, it showed that the drug was widely distributed in vivo or histone was highly bound to the drug. The AUC0-t of enrofloxacin in hemolymph, muscle and hepatopancreas were 187.34 mg·(L·h)-1, 132.15 mg·(kg·h)-1 and 1298.32 mg·(kg·h)-1, respectively, and the Vz of enrofloxacin in hemolymph was 2.63 L·kg-1. The t1/2z and CLz were the most important pharmacological parameters and were related to drug elimination. The t1/2z of enrofloxacin in hemolymph, muscle and hepatopancreas were 17.12 h, 72.31 h and 37.78 h, respectively, and the CLz were 0.11 L·(h·kg)-1, 0.21 kg·(h·kg)-1 and 0.023 kg·(h·kg)-1, respectively. It was obvious that enrofloxacin was rapidly absorbed, distributed and eliminated in Penaeus monodon. Ciprofloxacin, the metabolite of enrofloxacin, was detected in hemolymph, muscle and hepatopancreas, but the levels were low. The Cmax of ciprofloxacin in hemolymph, muscle and hepatopancreas were 1.07 mg·L-1, 0.77 mg·kg -1 and 1.40 mg·kg-1, respectively, which were about 6.00%, 15.30% and 1.45% of enrofloxacin in all three tissues, respectively. The AUC0-t of ciprofloxacin in hemolymph, muscle and hepatopancreas were 18.81 mg·(L·h)-1, 27.40 mg·(kg·h)-1 and 36.53 mg·(kg·h)-1, respectively. The ratios of the area under the curve of ciprofloxacin and enrofloxacin (AUCCIP/AUCENR) were 10.04 %, 20.73 % and 2.81 %, respectively, which was higher than that of Scylla serrata, Fenneropenaeus chinensis, and Paralichthys olivaceus, but significantly less than that of llamas, pigs and horses. It showed that that an intraspecies variability existed in the metabolite pathway among aquatic animals. In the present study enrofloxacin played the main role in Penaeus monodon. PKPD modeling was a significant strategy for providing an optimal dose regimen to prevent resistance problems. The model could establish the relationship between drug concentration, antimicrobial effect and time. Based on the scientific calculation, the model could provide the optimal dose regimen and dose interval. The most commonly used PKPD indices for enrofloxacin were the area under the concentrationversus time curve (AUC)/minimum inhibitory concentration (MIC) and peak plasma concentration (Cmax)/MIC. For concentrationdependent quinolone drugs enrofloxacin, Cmax/MIC=810, AUC/MIC=100, which could achieve good clinical treatment effect. Vibrio parahaemolyticus is an important pathogenic bacterium in mariculture animals and also an important pathogenic pathogen to shrimp. Referring to MIC of 36 strains of Vibrio parahemolyticus isolated from shrimp by Wei Wenjuan, the MIC90 was 2 mg·L-1, enrofloxacin was orally administered to Penaeus monodon at the dosage of 30 mg·kg -1, the estimated Cmax/MIC90 and AUC0-t/MIC90 were 8.91 and 93.67, respectively, which had good efficacy on bacterial diseases caused by Vibrio. As consumers pay more attention to food safety, drug residues in animalderived food have attracted much attention. Drug withdrawal period is the basis of scientific and rational drug use and has become an important means to control drug residues. According to the guidance published by China and European Union, the marker residue of ENR in fish is the sum of ENR and CIP with an MRL of 100 μg·kg -1, and the related tissue is muscle and adherent skin. The withdrawal time of enrofloxacin in Penaeus monodon was estimated to be 372.5 h (about 16 d) by WT1.4 software. The results can provide reference for scientific and rational use of enrofloxacin in Penaeus monodon.

Keywords: Penaeus monodon; enrofloxacin; pharmacokinetics; withdrawal time; oral administration