The Pharmacokinetics of tilmicosin in plasma and joint dialysate in an experimentally Mycoplasma synoviae infection model

Residue Depletion and Withdrawal Interval Estimations of Sulfamonomethoxine or Doxycycline Residues in Chinese Taihe Black-Bone Silky Fowls

Black-bone fowls are rich in melanin and regarded as being rich in nutritional value. However, the metabolism of antibiotics in black-bone fowls remains poorly understood. This study aimed to determine the tissue residue depletion kinetics of Sulfamonomethoxine (SMM) or Doxycycline in Taihe black-bone silky fowls. The tissue residue experiments involved a total of two hundred and forty Taihe black-boned silky fowls. The birds were raised to 100 days old in the same laboratory conditions and divided into a control group, SMM group, and Doxycycline group (80 birds for each group). The control group was provided normal drinking water. The SMM group was oral-administered SMM at concentrations of 50 mg/kg bw per day, and the Doxycycline group was oral-administered Doxycycline at concentrations of 40 mg/kg bw for 5 days, respectively. After the last dose, liver, kidney, muscle, and skin/fat were collected at various time points (0.16, 1, 3, 5, 7, 9, 12, 20, 30, and 40 days, eight birds for each time point). Concentrations of SMM or Doxycycline were analyzed using the UPLC-MS/MS method. The terminal elimination half-lives of SMM in muscle, skin/fat, liver, and kidney were 1.82 ± 1.24, 15.3 ± 4.97, 4.36 ± 1.49, and 5.42 ± 3.46 days, respectively, and 8.62 ± 2.82, 6.88 ± 2.06, 4.12 ± 1.28, and 1.53 ± 0.28 days for Doxycycline. The estimated withdrawal times (WDIs) of SMM were 4, 27, 10, and 12 days, while the estimated WDIs of Doxycycline were 18, 15, 4, and 6 days for muscle, skin/fat, liver, and kidney, respectively. The SMM or Doxycycline bioaccumulate in the skin/fat and may cause antimicrobial residues to be absorbed by human when the skin/fat is used in the diet. Doxycycline persists in muscle for a longer duration compared to SMM. This highlights the significance of muscle and skin/fat as a target organ for future food safety research.

Residue depletion and withdrawal time estimation of tilmicosin in black-bone silky fowls after administration via drinking water

In this study, residue depletion and withdrawal time estimation of tilmicosin were examined in Taihe black-bone silky fowls (TBSFs) after oral administration for three consecutive days at a dose of 75 mg/L in water. The tilmicosin concentrations in liver, kidney, muscle, and skin/fat of TBSFs collected from different time points (0.16, 1, 3, 5, 7, 9, 12, 20, 30, 40 days after last administration) were determined by UPLC-MS/MS. The results indicated that the tilmicosin concentrations in TBSFs tissues varied significantly, and kidney had the highest average concentrations (2604.65 ± 4625.20 μg/kg), followed by liver (1125.54 ± 1479.24 μg/kg), skin/fat (372.81 ± 428.33 μg/kg), and muscle (104.52 ± 143.95 μg/kg). Meanwhile, tilmicosin was still detected in all the four studied tissues (liver, kidney, skin/fat, and muscle) of TBSFs at the last time point (40th day after administration), suggesting that tilmicosin in TBSFs depleted slowly. Based on our experiments, the recommended withdrawal time of tilmicosin for TBSFs after oral administration for three consecutive days at a dose of 75 mg/L in water should be 32 days, which is much longer than the duration specified by Chinese regulatory authorities (10 days), and the abundance of melanin in TBSFs might be responsible for this phenomenon. Hence, a special use and withdrawal procedure of veterinary drugs in TBSFs is needed, and it is essential to focus on potential involvement of melanin in tilmicosin accumulation.

The pharmacokinetics/pharmacodynamics integration of tilmicosin against Mycoplasma synoviae in vitro and in vivo

Mycoplasma synoviae (MS) infection is a serious threat to poultry industry in China. Tilmicosin is a semisynthetic macrolide antibiotic used only in animals and has shown potential efficacy against MS, but there were no reported articles concerning the pharmacokinetics/pharmacodynamics (PK/PD) interactions of tilmicosin against MS in vitro and vivo. This study aimed to assess the antibacterial activity of tilmicosin against MS in vitro and in vivo using PK/PD model to provide maximal efficacy. The minimum inhibitory concentration (MIC) and killing rates of different drug concentrations were measured using the microdilution method in vitro. Then, tilmicosin was administered orally to the MS-infected chickens at doses of 7.5 and 60 mg/kg, and the PK parameters of tilmicosin in joint dialysates were determined using high-pressure liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) combined with the microdialysis technique. The antibacterial effect (△E) was calculated when the infected chickens were administered a single oral dose of tilmicosin at 4, 7.5, 15, 30, and 60 mg/kg b.w. The PK and PD data were fitted using the Sigmoid Emax model to evaluate the PK/PD interactions of tilmicosin against MS. The bactericidal activity of tilmicosin against MS was concentration dependent. Furthermore, the PK/PD index of AUC0-72h/MIC exhibited the most optimal fitting results (R2 = .98). The MS load decreased by 1, 2, and 3 Log10 CFU/mL, then AUC/MIC was determined as 13.99, 20.53, and 28.23 h, respectively, and the bactericidal effect can be achieved when the dose of MS-infected chickens is at 31.64 mg/kg b.w. The findings of this study hold significant implications for optimizing the treatment regimen for MS infection.

Disposition kinetics and tissue residues of tilmicosin following intravenous, subcutaneous, single and multiple oral dosing in geese (Anser anser domesticus)

Tilmicosin (TMC), a semi-synthetic macrolide antibiotic, is widely used in veterinary medicine due to its broad-spectrum, bacteriostatic properties. Frequently administered in various birds species, it is likely used off-label in geese as well. The study sought to investigate TMC's pharmacokinetics, tissue residues, in geese through in vivo experiments. The study involved longitudinal open studies on 15 healthy adult males, with three phases separated by one-month washout periods. Geese were administered TMC through intravenous (IV, 5 mg/kg), subcutaneous (SC, 10 mg/kg), and oral (PO, 25 mg/kg for five consecutive days) routes, with blood samples drawn at specific intervals. Tissue samples were also collected for subsequent analysis at pre-assigned times. TMC in goose plasma was quantified by a fully validated HPLC method. Plasma concentrations were quantified up to 4 hr for the PO and IV routes, and up to 10 hr in the SC route. Significant variations in bioavailability were observed between SC (87%) and PO (4%) routes. The body extraction ratio was low at 0.03, suggesting minimal ability of the liver and kidneys to eliminate TMC. Multiple oral doses showed no plasma accumulation, but tissue data revealed extensive distribution and prolonged residence, up to 120 h, suggesting a sustained therapeutic effect despite the brief plasma half-life. Regarding the multiple PO doses, provisional withdrawal times of 6, 7.5, and 8 days were suggested for the liver, muscles, and kidneys, respectively, according to the MRL set for these matrices in chickens by EMA. In conclusion, while the practical oral administration is discouraged at the population level, SC administration of TMC may be appropriate for geese, albeit impractical for flock therapy.

Pharmacokinetics of tilmicosin in plasma, urine and feces after a single intragastric administration in donkey (Equus asinus)

Tilmicosin, a macrolide antibiotic, has the potential to treat bacterial infections in donkeys. However, the pharmacokinetics of tilmicosin in donkeys have not been reported. The aim of this study was to investigate the pharmacokinetics of tilmicosin in donkey plasma, urine, and feces after a single intragastric administration to determine the suitability of tilmicosin for donkeys. A total of 5 healthy male donkeys with similar body weights were selected. The donkeys were administered a single dose of 10 mg · kg-1 body weight (BW) tilmicosin by gavage. The concentrations of tilmicosin in plasma, urine, and feces were determined. The results showed that after a single intragastric administration of 10 mg · kg-1 body weight, tilmicosin in donkey plasma reached a maximum concentration of 11.23 ± 5.37 mg · L-1 at 0.80 ± 0.10 h, with a half-life of 14.49 ± 7.13 h, a mean residence time of 28.05 ± 3.05 h, a Cl/F of 0.48 ± 0.18 L · kg-1 · h-1, and a Vd/F of 9.28 ± 2.63 Lkg-1. The percentage of tilmicosin excreted through the urine of donkeys is 2.47%, and the percentage excreted through the feces is 66.43%. Our study provides data to inform the use of tilmicosin in donkeys.

Depletion of tilmicosin residue in Gushi chickens following oral administration via drinking water

This study aimed to examine the depletion of tilmicosin residues in Gushi chickens following the administration at a concentration of 75 mg/L in their drinking water for three consecutive days. Plasma, liver, kidney, lung, muscle, and skin + fat samples were collected from 6 chickens at 6 h, 1, 3, 5, and 7 days after the treatment. Tilmicosin concentrations in the samples were determined using a high-performance liquid chromatography (HPLC) method. The findings revealed that the highest tilmicosin residues were detected in the liver, followed by the kidney, lung, skin + fat, muscle, and plasma. Notably, at 7 days post-treatment, no drug residue was detected in all samples except for the liver and kidney. The non-compartmental model was employed to calculate relevant pharmacokinetic parameters. The elimination half-lives (t1/2λz ) of tilmicosin were as follows, ranked from long to short: skin + fat (45.42 h), liver (44.17 h), kidney (40.06 h), plasma (37.64 h), lung (31.39 h), and muscle (30.05 h). Considering the current residue depletion and the maximum residue limits (MRLs) set by Chinese regulatory authorities, the withdrawal times for tilmicosin were estimated as 18.91, 10.81, and 8.58 days in the kidney, liver, and skin + fat, respectively. A rounded-up value of 19 days was selected as the conclusive withdrawal time. Furthermore, based on the observed tilmicosin concentrations in plasma and lung, combined with previously reported minimum inhibitory concentration (MIC) values against Mycoplasma gallisepticum, the current dosing regimen was deemed adequate for treating Mycoplasma gallisepticum infections in Gushi chickens.