Pharmacokinetics, safety and tissue residues of sustained-release sulfamethazine in sheep

Maximum levels of cross-contamination for 24 antimicrobial active substances in non-target feed. Part 11: Sulfonamides

The specific concentrations of sulfonamides in non-target feed for food-producing animals, below which there would not be an effect on the emergence of, and/or selection for, resistance in bacteria relevant for human and animal health, as well as the specific antimicrobial concentrations in feed which have an effect in terms of growth promotion/increased yield were assessed by EFSA in collaboration with EMA. Details of the methodology used for this assessment, associated data gaps and uncertainties, are presented in a separate document. To address antimicrobial resistance, the Feed Antimicrobial Resistance Selection Concentration (FARSC) model developed specifically for the assessment was applied. However, due to the lack of data on the parameters required to calculate the FARSC, it was not possible to conclude the assessment until further experimental data are available. To address growth promotion, data from scientific publications obtained from an extensive literature review were used. Levels in feed that showed to have an effect on growth promotion/increased yield were identified for three sulfonamides: sulfamethazine, sulfathiazole and sulfamerazine. It was recommended to carry out studies to generate the data that are required to fill the gaps which prevented the calculation of the FARSC for these antimicrobials.

Levers to Improve Antibiotic Treatment of Lambs via Drinking Water in Sheep Fattening Houses: The Example of the Sulfadimethoxine/Trimethoprim Combination

To limit the spread of bacterial diseases in sheep fattening houses, antibiotics are often administered collectively. Collective treatments can be delivered by drinking water but data on the drug’s solubility in water or on plasma exposure of the animals are lacking. We first assessed the solubility of products containing sulfadimethoxine (SDM), associated or not with trimethoprim (TMP), in different waters. We then compared in lambs the SDM and TMP pharmacokinetic profiles after individual intravenous (IV) and oral administrations of SDM-TMP in experimental settings (n = 8) and after a collective treatment by drinking water with SDM-TMP or SDM alone in a sheep fattening house (n = 100 for each treatment). The individual water consumption during the collective treatments was also monitored to characterize the ingestion variability. We showed that TMP had a short terminal half-life and very low oral bioavailability, demonstrating that it would be unable to potentiate SDM by oral route. Conversely, SDM had a long terminal half-life of 18 h and excellent oral bioavailability. However, delivery by drinking water resulted in a very high interindividual variability of SDM plasma concentrations, meaning that although disease spread could be controlled at the group level, some individuals would inevitably be under- or over-exposed to the antibiotic.

Oral absorption profiles of sulfonamides in Shiba goats: a comparison among sulfadimidine, sulfadiazine and sulfanilamide

The oral pharmacokinetics of three sulfonamides, sulfadimidine (pKa 7.5), sulfadiazine (pKa 6.5) and sulfanilamide (pKa 10.5), with different rates of unionization in rumen juice, were compared in Shiba goats to clarify the relationship between drug absorption profiles after their oral administration as well as their degree of unionization in the rumen. Sulfonamides were administered either into the left jugular vein or orally to five male goats at doses of 10 mg/kg body weight, using a crossover design with at least a 3-week washout period. The Tmax of sulfadimidine, sulfadiazine and sulfanilamide reached 2.0 ± 1.2, 6.0 ± 0.0, and 7.8 ± 1.6 hr, respectively, after their oral administration, and this was followed by their slow elimination due to a slow rate of drug absorption from the gastrointestinal tract. The MAT and t1/2ka of sulfadiazine (13.2 ± 2.0 and 10.9 ± 1.08 hr) were significantly longer than those of sulfanilamide (9.09 ± 1.67 and 7.46 ± 1.70 hr) and sulfadimidine (7.52 ± 0.85 and 5.17 ± 0.66 hr). These results suggest that the absorption rates of highly unionized drugs (such as sulfanilamide and sulfadimidine) from the forestomach of goats may be markedly higher than less unionized ones (such as sulfadiazine). The mean oral bioavailability of sulfadiazine was high (83.9 ± 17.0%), whereas those of sulfadimidine and sulfanilamide were low (44.9 ± 16.4% and 49.2 ± 2.11%, respectively).

Effects of age on the pharmacokinetics of single dose sulfamethazine after intravenous administration in cattle

Sulphonamides are still being used widely, influenced by the low cost and the efficacy against many common bacterial infections, since they present a broad spectrum of activity. The aim of this study was to determine the effect of age on the pharmacokinetic/pharmacodynamics (PK/PD) integration of intravenous sulfamethazine (60 mg/kgbw) in cattle, and the possible therapeutic outcomes. Six healthy female calves, at the age of one, three, seven and fifteen weeks were used. Normality analysis was assessed with the Shapiro-Wilk test. Non-parametric tests for paired data were used. Plasma concentrations were quantified using HPLC/uv. Differences were found between one-three-weeks-old calves and seven-fifteen-weeks-old calves, in pharmacokinetic parameters (clearance, area under the concentration-time curve and elimination half-life) and in the PK/PD integration. The ratios obtained in PK/PD integration (T>MIC, WAUC) confirm that it is necessary to apply twice the dose of sulfamethazine in > or = 7 weeks-old cattle to reach a satisfactory dosage regimen (MIC > or = 32 microg/mL).

Comparison of bovine in vivo bioavailability of two sulfamethazine oral boluses exhibiting different in vitro dissolution profiles

The bolus (or oblet) is a dosage form that can be used for the oral administration of pharmaceutical compounds to ruminating species. Unlike traditional tablets, oral boluses may contain quantities of drug on the order of grams rather than milligrams. Due to its size, it is only recently that USP-like in vitro dissolution methods have been developed for this dosage form. However, whether or not these dissolution tests can predict product in vivo performance has yet to be determined. The importance of this issue is apparent when the U.S. Food and Drug Administration Center for Veterinary Medicine is faced with the decision of whether to require additional in vivo bioequivalence study data to support the approval of changes in product chemistry or manufacturing method. The current study was undertaken to determine whether an in vivo/in vitro correlation can be established for bovine sulfamethazine oral boluses and to acquire insight into the magnitude of changes in in vitro product performance that can occur before corresponding changes are seen in in vivo blood level profiles. Based upon the results of this investigation, it is concluded that marked changes in in vitro sulfamethazine bolus performance can be tolerated before resulting in altered in vivo blood level profiles. However, the data also suggest that rumenal absorption may occur for some compounds. Therefore the degree to which variation in product in vitro dissolution profiles can be tolerated may be compound specific.

Transfer of sulphamethazine from contaminated dairy feed to cows' milk

Four groups of four healthy mid-lactation Friesian cows were fed a compound feeding stuff containing either 2, 10 or 250 mg sulphamethazine/kg, corresponding to 0, 2, 10 and 250 per cent of the therapeutic inclusion rate in rations for pigs, at a flat rate of 3 kg twice daily for 21 days, followed by a seven-day withdrawal period. The cows were machine-milked twice daily and pooled milk samples from each cow were analysed by a commercially available microbiological assay with a sensitivity of 100 micrograms/litre and by a high performance liquid chromatography (HPLC) procedure with a limit of detection of 10 micrograms/litre. No sulphamethazine was detected by HPLC in the milk samples taken from any of the cows fed the concentrate containing 2 or 10 mg/kg. The milk samples from all four cows fed the highest concentration of sulphamethazine contained from 21 to 120 micrograms/litre while they were being fed the contaminated concentrate. The cow with the highest concentrations of sulphamethazine was the only one which repeatedly tested positive by the microbiological assay. The concentration of sulphamethazine declined rapidly during the withdrawal period and the drug was not detectable by either method in samples taken from two days after the contaminated feed was withdrawn.

Relative bioavailability of microgranulated sulfadimidine in veal calves

The kinetics of free and microgranulated sulfadimidine were compared in milk-fed calves dosed orally (180 mg/kg) in a crossover study. Microgranulation results in delayed absorption of sulfadimidine and poor bioavailability, with the area under the plasma concentration-time curve (AUC(0-infinity)) reduced from 7400 to 3781 micrograms.h/mL, and maximum plasma concentration (Cmax) reduced from 188.1 +/- 39.0 to 84.41 +/- 22.6 micrograms/mL. It is concluded that sulfadimidine microgranulated with long chain fatty acids is not suitable for use in milk-fed calves; the gastrointestinal transit time is too rapid to allow full release of the drug, markedly limiting its bioavailability. In adult animals, or in the young of other animal species in which digesta transit time is slower than in calves, the bioavailability of microgranulated sulfadimidine may be much greater.