Pharmacokinetic-pharmacodynamic modelling for the determination of optimal dosing regimen of florfenicol in Nile tilapia (Oreochromis niloticus) at different water temperatures and antimicrobial susceptibility levels

Optimized dosing regimen is key to the effective use of antibacterials and to minimizing drug-related side effects. The current study established a pharmacokinetic–pharmacodynamic (PK-PD) model for the determination of optimal antibacterial dosing regimen in fish taken into consideration the temperature-dependent PK and the pathogen-dependent antimicrobial susceptibility, using florfenicol (FF) in Nile tilapia as an example. The calculated optimal dosages significantly varied by temperature and target MIC levels, ranging from 2.23 (MIC 1 µg/ml at 24°C) to 34.88 mg kg−1 day−1 (MIC 4 µg/ml at 32°C). The appropriateness of the calculated dosages was successfully verified by the in vivo studies. After 5 days of oral administration of the calculated optimal dosage at 24°C, the predicted plasma drug values were in line with the mean observed Cmin(ss) while at 28 and 32°C underestimation of the Cmin(ss) in a dose-dependent manner was observed and likely due to the occurrence of non-linear PK at high dosages. The averaged serum protein binding of FF was 19.1%. Our results demonstrated the appropriateness and clinical applicability of the developed PK-PD approach for the determination of optimal dosing regimens at given temperatures and MICs. Saturation metabolism and PK non-linearity of FF in tilapia warrant further study

Reduced Resident Time and Tissue Residues of Synergistic Florfenicol-Thiamphenicol Combination in Leghorn Chickens

In vivo synergistic antimicrobial effects against pathogens in chickens have been reported for florfenicol (FF) and thiamphenicol (TAP) at a ratio of 1:2. The present study evaluates the pharmacokinetics and tissue residues of a single combined intramuscular treatment of FF+TAP at 1/6 and 1/3 of their respective recommended doses in 5-week old broiler chickens. The drug concentrations were determined by LC/MS/MS. Significant reductions were observed in the Cmax (0.045 and 2.64 µg/mL for FF and TAP, respectively) and AUC (0.13 and 7.19 h•µg/mL for FF and TAP, respectively) compared to corresponding values reported for the recommended dose (up to two orders of magnitude lower). Tissue FF (10.6-88.4 µg/kg) and TAP concentrations (6.5-147.0 µg/kg) declined below the maximum residue limit within only one day except for TAP residue in skin/fat. This experiment provided supporting evidence for a complete study that synergistic FFTAP has potential benefits over monotherapy since drug residues could be greatly reduced; much shorter withdrawal period was strongly indicated. [ABSTRACT FROM AUTHOR

The Use of Tricaine Methanesulfonate (MS-222) in Asian Seabass (<i>Lates calcarifer</i>) at Different Temperatures: Study of Optimal Doses, Minimum Effective Concentration, Blood Biochemistry, Immersion Pharmacokinetics, and Tissue Distributions

This study was conducted to determine the optimal doses and minimum effective concentrations (MECs) of tricaine methanesulfonate (MS-222) in marketable-size Asian seabass reared at two temperatures (22 and 28 °C). Serum biochemical parameters, pharmacokinetics, and tissue distributions of MS-222 following immersion at the determined optimal doses were also evaluated in order to delineate possible mechanisms dictating the temperature difference. The definition of optimal dose is set as the dose when fish attain stage III anesthesia within 5 min, sustain this stage for 3 min, and re-attain equilibrium within 5 min. The MEC is the fish serum MS-222 concentration when stage III anesthesia is reached. The results showed that water temperature exerted no or minimal impact on the designated parameters. The optimal doses at 22 and 28 °C were 140 and 150 µg/mL, while the MECs were 70.48 and 78.27 µg/mL, respectively. Fish exposed to the optimal doses of MS-222 had significantly elevated blood concentrations of lactate, glucose, calcium, magnesium, and sodium, while the blood pH was significantly decreased. The fish eliminated MS-222 faster at 28 °C than at 22 °C, with serum half-lives of 18.43 and 37.01 h, respectively. Tissue-specific distribution patterns were evident. Irrespective of water temperature, MS-222 peaked at 5 min for the brain and gill but peaked slightly later at 10–20 min for the liver and kidney. Most tissues exhibit a gradual decline of drug concentration except for the gill, which was maintained at a steady level. Muscle is the least perfused tissue with the lowest drug concentration throughout the 90 min period. This study provided physiological and pharmacokinetic evidence contributing to a better understanding of the actions of MS-222 in Asian seabass at different temperatures

Effects of dietary yeast-derived nucleotide and RNA on growth performance, survival, immune responses, and resistance to Vibrio parahaemolyticus infection in Pacific white shrimp (Litopenaeus vannamei)

Nucleotides (NT) and RNA from yeast extracts are gaining interest as high-value feed additives. The present study intended to evaluate the influences of yeast derived-NT and RNA on the growth performance, survival, immune responses, and resistance to Vibrio parahaemolyticus infection in Pacific white shrimp. In Experiment 1, postlarvae were distributed into 7 groups, corresponding to 7 experimental diets: control, NT 0.25, NT 0.50, NT 0.75, RNA 0.25, RNA 0.50, and RNA 0.75 g/kg feed. They were fed the experimental diets for 45 days. Then, their body weights, survival rates, immune parameters, and Vibrio spp. counts in the hepatopancreas and intestines were determined. In Experiment 2, the shrimp from Experiment 1 were challenged by immersion with V. parahaemolyticus at 105 CFU/mL. Each group was fed the same diet for another 10 days to assess the disease resistance performance. The results revealed that the shrimp body weights of all groups were similar suggesting that neither NT nor RNA exerts the growth-promoting effect. However, the average survival rates of the NT and RNA groups were in the range of 89–93 %, significantly higher than that of the control (83 %). These increased survivals were in line with the reduction in the hepatopancreatic and intestinal Vibrio spp. counts and the elevated immune parameters in the NT and RNA-fed shrimp. At day 10 after the bacterial challenge, the highest survival rates were observed in the RNA 0.50 and 0.75 g/kg feed groups (81 % and 82 %, respectively), followed by the RNA 0.25 (70 %) and NT 0.75 g/kg feed (68 %), and significantly higher than the positive control (54 %). In short, both yeast-derived NT and RNA, especially the RNA at the dose of 0.50–0.75 g/kg feed groups, showed promising health benefits effects in the Pacific white shrimp, notably the improved immune function and disease resistance

Temperature-dependent non-linear pharmacokinetics of florfenicol in Nile tilapia (Oreochromis niloticus) and its implementation in optimal dosing regimen determination

While the majority of drugs used clinically at therapeutic range usually follow dose-independent or linear pharmacokinetics (PK); as the administered dose is increased the PK behavior may become dose-dependent or non-linear without recognition and may lead to adverse effects. The current study aimed to investigate the extent of non-linear PK of florfenicol (FF) in Nile tilapia, and for the first time, to investigate the effect of temperature on non-linear PK behavior. For each temperature level (24, 28, and 32 °C), the fish were orally administered with FF at a single dose of 10, 15, 30 and 45 mg/kg. The serum concentrations of FF were analyzed by HPLC-UV and the PK parameters were determined by 2-compartmental model. Regardless of the rearing temperature level, increasing the FF doses from 10 to 45 mg/kg resulted in about 1.3–1.5 fold increases in the dose-normalized area under the serum concentration-time curve (AUC/dose), longer elimination half-life (t1/2β), and slower clearance (CL/F). The dose-dependency of the above parameters but not absorption half-life (t1/2Ka) and volume of distribution (Vd) suggested that the FF non-linearity was most likely due to saturation of metabolism. For the first time, the effect of temperature on non-linearity was revealed and discovered that the non-linearity happened at lower dose in the warmer temperature (≥ 30 mg/kg at 28 and 32 °C) than in the cooler temperature (≥ 45 mg/kg at 24 °C), which correlated well with the lower Michaelis-Menten constant (Km) at the warmer temperature. In the presence of non-linear PK, a modified Michaelis-Menten equation could be successfully applied to determine an optimal dosing regimen. The accuracy of the calculated dosage was verified by the oral multiple-dose study. Medication of Nile tilapia with a high dose of FF should be done with great caution especially at the warmer water as higher dosage may be required and that non-linearity may happen at lower dose such that it would cause a higher risks of drug toxicity and tissue residue violation

Bath immersion pharmacokinetics of florfenicol in Nile tilapia (Oreochromis niloticus)

Drug administration by immersion can be a preferable method in certain conditions especially for treating small-sized, anorexic, or valuable fish. Pharmacokinetic information regarding bath treatment is considerably lacking in comparison to other common administration routes. The current study aimed to investigate if immersion can be an effective route to administer florfenicol (FF) for treatment in Nile tilapia. Nile tilapia reared at 28°C were immersed with FF solution at concentrations of 50, 100, 200, 500, and 500/200 (3 hr/117 hr) ppm for 120 hr and moved to drug-free freshwater for another 24 hr. The serum FF concentration in 100, 200, and 500/200 ppm groups reached steady-state at 12 hr with concentrations of 2.44, 3.04, and 5.26 µg/ml, respectively, which were about 2% of the bathing concentrations. The target therapeutic levels of 1–4 µg/ml were attained and maintained within 1–12 hr, depending on the immersion concentration and the target MIC. Serum FF reached the target with shorter time at higher bathing concentration. Following the 120-hr bath, the serum FF declined with the first-order half-life of approximately 10 hr. A minimum of 100 ppm FF is required for treatment purpose, and an initial high loading concentration followed by maintenance concentration is a plausible way to reach in vivo therapeutic level in short time. Greater than 99% of the residual FF in the bathing water could be removed within 15 min by 0.05% NaOCl. Our results indicated that bath immersion is a promising potential route for FF administration in Nile tilapia

Temperature-dependent pharmacokinetics of florfenicol in Nile tilapia (Oreochromis niloticus) following single oral and intravenous administration

Temperature-dependent pharmacokinetics (PK) have rarely been reported in tilapia despite there are popularly cultured worldwide, ranging from tropical to temperate climates. The present study aims to investigate the PK characteristics of florfenicol (FF) in Nile tilapia at 3 temperature levels (24, 28, and 32 °C) after single intravenous (IV) and oral (PO) dose of 15 mg/kg to evaluate the effects of temperature on PK. The serum concentrations of FF were analyzed by HPLC-UV method and PK characteristics were analyzed by 2-compartmental model. It was revealed that temperature has profound influences on certain PK parameters. The results from both IV and PO experiments were generally similar. Increasing water temperature from 24 to 32 °C led to significantly increased elimination rate constant (β) from 0.056 to 0.095 1/h and shortened elimination half-life (t1/2β) from 12–13 h to 7–8 h. The absorption half-life (t1/2Ka) were decreased from 2.28 to 1.18 h as well as the maximum serum concentration (Cmax) from 23.14 to 16.71 μg/mL and time to reach Cmax (Tmax) from 1.40 to 0.75 h. The area under the serum concentration-time curves (AUC) were reduced by half while the clearances were doubled and the volume of distributions (Vd) were significantly increased. Our results also demonstrated that for FF in Nile tilapia the temperature coefficient (Q10) values could be applied to predict the CL and β at a specific temperature with high accuracy (94–116%). The temperature-sensitive PK parameters such as the increase in Ka, Vd, and β significantly affected the serum concentrations and its overall exposure (AUC), thereby could potentially implicate that proper dosing regimen should take water temperature into consideration. The study highlighted the possibility of water temperature effect on therapeutic outcome of FF used in tilapia and likely other cichlids

Salinity-dependent pharmacokinetics of florfenicol in Nile tilapia (Oreochromis niloticus) and its implication in optimal dosing regimen

Nile tilapia has been cultured in a wide salinity range, from freshwater to up to 15 ppt brackish water due to its euryhaline characteristics. As salinity profoundly affects the physiology of freshwater and seawater fish in a different way, it is conceivable that pharmacokinetic (PK) behavior should also exhibit salinity-dependency. The current study aimed to investigate the effect of salinity on PK of florfenicol (FF) in Nile tilapia reared at 0, 2, 4, 8, and 15 ppt after a single intravenous (IV) or oral (PO) administration of 15 mg/kg at 28 °C. The implication of salinity-dependent PK in the optimal dosing regimen determination was also examined. The serum concentrations of FF were analyzed by HPLC-UV method and PK parameters were determined by the 2-compartmental model. Following IV injection, increasing water salinity from 2 to 15 ppt lead to a shorter elimination half-life (t1/2β) from 11.22 to 9.03 h, faster drug clearance (CL) from 0.047 to 0.056 L/kg/h, and smaller area under the serum concentration-time curve (AUC) from 326.19 to 267.74 h·μg/mL, suggesting a more rapid elimination at a higher salinity level. The results from PO study were generally consistent with the IV experiment except for the unchanged AUC over a salinity range of 0 to 15 ppt likely due to greater bioavailability at higher salinity. However, the absorption rate of FF was not significantly influenced by salinity as there were no significant differences in t1/2Ka, Cmax, and Tmax among the 5 salinity levels. The optimal dosing regimens were determined by the pharmacokinetic-pharmacodynamic approach for each salinity level and it was revealed that the calculated dosages were similar between 0 and 8 ppt salinity, but a higher dosage was required at 15 ppt (from 7 to 10 mg/kg/day at the MIC of 2 μg/mL). Therefore, Nile tilapia reared at saltwater required a higher FF dosage than those cultured at freshwater

Assessment of veterinary drugs in plants using pharmacokinetic approaches: The absorption, distribution and elimination of tetracycline and sulfamethoxazole in ephemeral vegetables.

The present study was carried out to demonstrate novel use of pharmacokinetic approaches to characterize drug behaviors/movements in the vegetables with implications to food safety. The absorption, distribution, metabolism and most importantly, the elimination of tetracycline (TC) and sulfamethoxazole (SMX) in edible plants Brassica rapa chinensis and Ipomoea aquatica grown hydroponically were demonstrated and studied using non-compartmental pharmacokinetic analysis. The results revealed drug-dependent and vegetable-dependent pharmacokinetic differences and indicated that ephemeral vegetables could have high capacity accumulating antibiotics (up to 160 μg g-1 for TC and 38 μg g-1 for SMX) within hours. TC concentration in the root (Cmax) could reach 11 times higher than that in the cultivation fluid and 3-28 times higher than the petioles/stems. Based on the volume of distribution (Vss), SMX was 3-6 times more extensively distributed than TC. Both antibiotics showed evident, albeit slow elimination phase with elimination half-lives ranging from 22 to 88 hours. For the first time drug elimination through the roots of a plant was demonstrated, and by viewing the root as a central compartment and continuous infusion without a loading dose as drug administration mode, it is possible to pharmacokinetically monitor the movement of antibiotics and their fate in the vegetables with more detailed information not previously available. Phyto-pharmacokinetic could be a new area worth developing new models for the assessment of veterinary drugs in edible plants

In vitro and in vivo Synergistic Effects of Florfenicol and Thiamphenicol in Combination Against Swine Actinobacillus pleuropneumoniae and Pasteurella multocida

Potential synergism between florfenicol (FF) and thiamphenicol (TAP) was investigated for in vitro efficacy against Actinobacillus pleuropneumoniae and/or Pasteurella multocida as well as in vivo efficacy in swine. Among isolates of A. pleuropneumoniae (n = 58) and P. multocida (n = 79) from pigs in Taiwan that were tested, high percentages showed resistance to FF (52 and 53%, respectively) and TAP (57 and 53%, respectively). Checkerboard microdilution assay indicated that synergism [fractional inhibitory concentration index (FICI) ≤ 0.5] was detected in 17% of A. pleuropneumoniae (all serovar 1) and 24% of P. multocida isolates. After reconfirming the strains showing FICI ≤ 0.625 with time kill assay, the synergism increased to around 32% against both bacteria and the number could further increase to 40% against resistant A. pleuropneumoniae and 65% against susceptible P. multocida isolates. A challenge-treatment trial in pigs with P. multocida showed that the FF + TAP dosage at ratios correspondent to their MIC deduction was equally effective to the recommended dosages. Further on the combination, the resistant mutation frequency is very low when A. pleuropneumoniae is grown with FF + TAP and similar to the exposure to sub-inhibitory concentration of FF or TAP alone. The degree of minimum inhibitory concentration (MIC) reduction in FF could reach 75% (1/4 MIC) or more (up to 1/8 MIC for P. multocida, 1/16 for A. pleuropneumoniae) when combined with 1/4 MIC of TAP (or 1/8 for A. pleuropneumoniae). The synergism or FICI ≤ 0.625 of FF with oxytetracycline (47%), doxycycline (69%), and erythromycin (56%) was also evident, and worth further investigation for FF as a central modulator facilitating synergistic effects with these antimicrobials. Taken together, synergistic FF + TAP combination was effective against swine pulmonary isolates of A. pleuropneumoniae and P. multocida both in vitro and in vivo. Thus, this study may offer a potential alternative for the treatment of A. pleuropneumoniae and P. multocida infections and has the potential to greatly reduce drug residues and withdrawal time