Multiresidue Determination of 27 Sulfonamides in Poultry Feathers and Its Application to a Sulfamethazine Pharmacokinetics Study on Laying Hen Feathers and Sulfonamide Residue Monitoring on Poultry Feathers.

A method for the simultaneous determination of 27 sulfonamides in poultry feathers using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was established in this study. The samples were extracted using 0.1 mol/L HCl solutions in a 60 °C water bath for 2 h, purified using hydrophilic-lipophilic balance solid-phase extraction, nitrogen-dried, and then reconstituted for UPLC-MS/MS analysis, which was performed with a CSH-C18 column. Linearity, limit of detection, limit of quantification, recovery, and precision were calculated in accordance with Commission Decision 2002/657/EC. For linearity, all standard curves showed a standard coefficient greater than 0.99, and the recoveries and coefficient of variation were 89-115% and <20%, respectively. The limit of detection and limit of quantification were 0.2-5 and 0.5-20 ng/g, respectively. The method was successfully applied to sulfamethazine (SMZ) residue accumulation monitoring in laying hen feathers and sulfonamide residue monitoring on poultry feathers. SMZ residue accumulation in the laying hen feathers was studied after administration with 100 mg/kg of SMZ for 21 consecutive days. SMZ residues were still detected in feathers 14 days after drug administration and persisted for up to 85 days. Results from 42 poultry feather samples showed that the feather is a suitable medium to monitor the illegal use of sulfonamides in poultry production.

Effect of composting and soil type on dissipation of veterinary antibiotics in land-applied manures.

The objective of this study was to determine the fate of commonly used veterinary antibiotics in their naturally excreted form when manure-based amendments are applied to soil. Beef cattle were administered sulfamethazine, tylosin, and chlortetracycline and dairy cows were treated with pirlimycin. The resulting manure was composted for 42 d under static or turned conditions and applied at agronomic N rates to sandy, silt, and silty clay loam soils and compared with amendment with corresponding raw manures in sacrificial microcosms over a 120-day period. Antibiotic dissipation in the raw manure-amended soils followed bi-phasic first order kinetics. The first phase half-lives for sulfamethazine, tylosin, chlortetracycline, and pirlimycin ranged from 6.0 to 18, 2.7 to 3.7, 23 to 25, and 5.5-8.2 d, respectively. During the second phase, dissipation of sulfamethazine was negligible, while the half-lives for tylosin, chlortetracycline, and pirlimycin ranged from 41 to 44, 75 to 144, and 87-142 d, respectively. By contrast, antibiotic dissipation in the compost-amended soils followed single-phase first order kinetics with negligible dissipation of sulfamethazine and half-lives of tylosin and chlortetracycline ranging from 15 to 16 and 49-104 d, respectively. Pirlimycin was below the detection limit in the compost-amended soils. After incubating 120 d, antibiotics in compost-amended soils (up to 3.1 µg kg-1) were significantly lower than in manure-amended soils (up to 19 µg kg-1, p < .0001), with no major effect of soil type on the dissipation. Risk assessment suggested that composting can reduce antibiotic resistance selection potential in manure-amended soils.

Effects of piroxicam on tissue distribution of sulfadimidine in West African Dwarf male and female goats.

Cases of Stevens-Johnson syndrome have been increasingly reported in Nigeria by individuals who consumed meat products of animals especially goats injected sulfonamides. Hence, tissue distribution and residues of intramuscular sulfadimidine were studied in West African Dwarf (WAD) goats. Twenty goats divided into two groups of 10 each (five males; five females) weighing 10.4 ± 1.63 kg were administered intramuscular sulfadimidine (100 mg/kg body weight), and the second group was coadministered 5 mg/kg of piroxicam via right and left thigh muscle, respectively. Samples of the liver, kidney, spleen, heart, lung, intestine, brain, and skeletal muscle were collected into sterile cellophane bags. Two untreated goats were killed and used for preparation of tissue standards. The tissue samples were stored frozen for analysis. High concentration of sulfadimidine residues was found in all the tissues of goats administered sulfadimidine as well as tissues of goats coadministered sulfadimidine/piroxicam for up to 30 days postdrug administration. Generally, residues of sulfadimidine were observed to be significantly higher than the acceptable limit (0.1 ppm). Hence, consumption of meats from WAD goats administered sulfadimidine may pose very high risk of Stevens-Johnson syndrome in sensitive humans. As such consumption of such meats should be avoided.

Optimising the in vitro and in vivo performance of oral cocrystal formulations via spray coating.

Engineering of pharmaceutical cocrystals is an advantageous alternative to salt formation for improving the aqueous solubility of hydrophobic drugs. Although, spray drying is a well-established scale-up technique in the production of cocrystals, several issues can arise such as sublimation or stickiness due to low glass transition temperatures of some organic molecules, making the process very challenging. Even though, fluidised bed spray coating has been successfully employed in the production of amorphous drug-coated particles, to the best of our knowledge, it has never been employed in the production of cocrystals. The feasibility of this technique was proven using three model cocrystals: sulfadimidine (SDM)/4-aminosalicylic acid (4ASA), sulfadimidine/nicotinic acid (NA) and ibuprofen (IBU)/ nicotinamide (NAM). Design of experiments were performed to understand the critical formulation and process parameters that determine the formation of either cocrystal or coamorphous systems for SDM/4ASA. The amount and type of binder played a key role in the overall solid state and in vitro performance characteristics of the cocrystals. The optimal balance between high loading efficiencies and high degree of crystallinity was achieved only when a binder: cocrystal weight ratio of 5:95 or 10:90 was used. The cocrystal coated beads showed an improved in vitro-in vivo performance characterised by: (i) no tendency to aggregate in aqueous media compared to spray dried formulations, (ii) enhanced in vitro activity (1.8-fold greater) against S. aureus, (iii) larger oral absorption and bioavailability (2.2-fold higher Cmax), (iv) greater flow properties and (v) improved chemical stability than cocrystals produced by other methods derived from the morphology and solid nature of the starter cores.

Genetic heterogeneity among slow acetylator N-acetyltransferase 2 phenotypes in cryopreserved human hepatocytes.

Genetic polymorphisms in human N-acetyltransferase 2 (NAT2) modify the metabolism of numerous drugs and carcinogens. These genetic polymorphisms modify both drug efficacy and toxicity and cancer risk associated with carcinogen exposure. Previous studies have suggested phenotypic heterogeneity among different NAT2 slow acetylator genotypes. NAT2 phenotype was investigated in vitro and in situ in samples of human hepatocytes obtained from various NAT2 slow and intermediate NAT2 acetylator genotypes. NAT2 gene dose response (NAT2*5B/*5B > NAT2*5B/*6A > NAT2*6A/*6A) was observed towards the N-acetylation of the NAT2-specific drug sulfamethazine by human hepatocytes both in vitro and in situ. N-acetylation of 4-aminobiphenyl, an arylamine carcinogen substrate for both N-acetyltransferase 1 and NAT2, showed the same trend both in vitro and in situ although the differences were not significant (p > 0.05). The N-acetylation of the N-acetyltransferase 1-specific substrate p-aminobenzoic acid did not follow this trend. In comparisons of NAT2 intermediate acetylator genotypes, differences in N-acetylation between NAT2*4/*5B and NAT2*4/*6B hepatocytes were not observed in vitro or in situ towards any of these substrates. These results further support phenotypic heterogeneity among NAT2 slow acetylator genotypes, consistent with differential risks of drug failure or toxicity and cancer associated with carcinogen exposure.

Rabbit N-acetyltransferase 2 genotyping method to investigate role of acetylation polymorphism on N- and O-acetylation of aromatic and heterocyclic amine carcinogens.

The rabbit was the initial animal model to investigate the acetylation polymorphism expressed in humans. Use of the rabbit model is compromised by lack of a rapid non-invasive method for determining acetylator phenotype. Slow acetylator phenotype in the rabbit results from deletion of the N-acetyltransferase 2 (NAT2) gene. A relatively quick and non-invasive method for identifying the gene deletion was developed and acetylator phenotypes confirmed by measurement of N- and O-acetyltransferase activities in hepatic cytosols. Rabbit liver cytosols catalyzed the N-acetylation of sulfamethazine (p = 0.0014), benzidine (p = 0.0257), 4-aminobiphenyl (p = 0.0012), and the O-acetylation of N-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP; p = 0.002) at rates significantly higher in rabbits possessing NAT2 gene than rabbits with NAT2 gene deleted. In contrast, hepatic cytosols catalyzed the N-acetylation of p-aminobenzoic acid (an N-acetyltransferase 1 selective substrate) at rates that did not differ significantly (p > 0.05) between rabbits positive and negative for NAT2. The new NAT2 genotyping method facilitates use of the rabbit model to investigate the role of acetylator polymorphism in the metabolism of aromatic and heterocyclic amine drugs and carcinogens.

Uptake and biodegradation of the antimicrobial sulfadimidine by the species Tripolium pannonicum acting as biofilter and its further biodegradation by anaerobic digestion and concomitant biogas production.

This project analyses the uptake and biodegradation of the antimicrobial sulfadimidine (SDI) from the culture medium and up to the anaerobic digestion. Tripolium pannonicum was grown under hydroponic conditions with different concentrations of SDI (0, 5 and 10mg·L(-1)) and the fresh biomass, containing different amounts of SDI taken up, was used as substrate for biogas production. SDI was analyzed by liquid chromatography coupled to positive ion electrospray mass spectrometry (ESI LC-MS). Based on the findings, T. pannonicum is able to uptake SDI. The more SDI is in the culture medium, the higher the SDI content in the plant tissue. According to this study, it is possible to produce high yields of biogas using biomass of T. pannonicum containing SDI and at the same time biodegradation of SDI is carried out. The highest specific biogas yield is obtained using shoots as substrate of the plants cultivated at 5mg·L(-1) SDI.

Human Food Safety Implications of Variation in Food Animal Drug Metabolism.

Violative drug residues in animal-derived foods are a global food safety concern. The use of a fixed main metabolite to parent drug (M/D) ratio determined in healthy animals to establish drug tolerances and withdrawal times in diseased animals results in frequent residue violations in food-producing animals. We created a general physiologically based pharmacokinetic model for representative drugs (ceftiofur, enrofloxacin, flunixin, and sulfamethazine) in cattle and swine based on extensive published literature. Simulation results showed that the M/D ratio was not a fixed value, but a time-dependent range. Disease changed M/D ratios substantially and extended withdrawal times; these effects exhibited drug- and species-specificity. These results challenge the interpretation of violative residues based on the use of the M/D ratio to establish tolerances for metabolized drugs.

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).

Application of in vivo microdialysis for investigation of unbound drug concentrations of intravenously administered sulfadimidine in the paranasal sinus mucosa of horses.

OBJECTIVE: To monitor concentrations of sulfadimidine in the paranasal sinus mucosa (PSM) of unsedated horses following IV administration of trimethoprim-sulfadimidine via in vivo microdialysis. ANIMALS: 10 healthy adult horses. PROCEDURES: Concentric microdialysis probes were implanted into the subepithelial layers of the frontal sinus mucosa of standing sedated horses. Four hours after implantation, trimethoprim-sulfadimidine (30 mg/kg) was administered IV every 24 hours for 2 days; dialysate and plasma samples were collected at intervals during that 48-hour period and analyzed for concentrations of sulfadimidine. The dialysate concentration and relative loss of sulfadimidine from the perfusate were used to calculate the PSM concentration. RESULTS: Microdialysis probe implantation and subsequent in vivo microdialysis were successfully performed for all 10 horses. Following the first and second administration of trimethoprim-sulfadimidine, mean ± SD peak concentrations of sulfadimidine were 55.3 ± 10.3 µg/mL and 51.5 ± 8.7 µg/mL, respectively, in plasma and 9.6 ± 4.5 µg/mL and 7.0 ± 3.3 µg/mL, respectively, in the PSM. Peak sulfadimidine concentrations in the PSM were detected at 5.9 ± 2.7 hours and 5.4 ± 2.3 hours following the first and second drug administrations, respectively. For 12 hours, mean PSM sulfadimidine concentration remained greater than the minimum inhibitory concentration indicative of sulfonamide susceptibility of equine bacterial isolates (4.75 µg/mL). CONCLUSIONS AND CLINICAL RELEVANCE: In vivo microdialysis for continuous monitoring of PSM sulfadimidine concentrations in unsedated horses was feasible. Intravenous administration of trimethoprim (5 mg/kg) and sulfadimidine (25 mg/kg) proved likely to be efficient for treating sinusitis caused by highly susceptible pathogens, providing that the dosing interval is 12 hours.

Tissue concentrations of sulfamethazine and tetracycline hydrochloride of swine (Sus scrofa domestica) as it relates to withdrawal methods for international export.

The use of water medications is a common practice in the US swine industry to treat and prevent infections in swine herds with minimal labor and without risk of needle breakage. There are concerns that FDA-approved withdrawal times (WDT) may be inadequate for several water medications when exporting pork products to countries where MRLs (maximum residue limits) are lower than US tolerance levels. In this study, withdrawal intervals (WDI) were estimated for pigs when dosed with tetracycline and sulfamethazine in water. The WDI were calculated using the FDA tolerance method (TLM) and a population-based pharmacokinetic method (PopPK). The estimated WDIs (14-16 days using TLM) were similar to the approved WDT of 15 days for sulfamethazine. However, the PopPK method extended WDIs for both sulfamethazine (19-20 days) and tetracycline (12 days) compared to the currently approved WDTs in the U.S. This study also identified potential differences in WDI between weanling and finisher pigs. In conclusion, the TLM may not always provide adequate WDT for foreign export markets especially when MRLs differ from tolerance levels approved for US markets. However, PopPK methods can provide conservative WDIs in situations with considerable variability in medication exposure such as with administration in water.

The effect of breed and sex on sulfamethazine, enrofloxacin, fenbendazole and flunixin meglumine pharmacokinetic parameters in swine.

Drug use in livestock has received increased attention due to welfare concerns and food safety. Characterizing heterogeneity in the way swine populations respond to drugs could allow for group-specific dose or drug recommendations. Our objective was to determine whether drug clearance differs across genetic backgrounds and sex for sulfamethazine, enrofloxacin, fenbendazole and flunixin meglumine. Two sires from each of four breeds were mated to a common sow population. The nursery pigs generated (n = 114) were utilized in a random crossover design. Drugs were administered intravenously and blood collected a minimum of 10 times over 48 h. A non-compartmental analysis of drug and metabolite plasma concentration vs. time profiles was performed. Within-drug and metabolite analysis of pharmacokinetic parameters included fixed effects of drug administration date, sex and breed of sire. Breed differences existed for flunixin meglumine (P-value<0.05; Cl, Vdss ) and oxfendazole (P-value<0.05, AUC0→∞ ). Sex differences existed for oxfendazole (P-value < 0.05; Tmax ) and sulfamethazine (P-value < 0.05, Cl). Differences in drug clearance were seen, and future work will determine the degree of additive genetic variation utilizing a larger population.

Acetylator status and N-acetyltransferase 2 gene polymorphisms; phenotype-genotype correlation with the sulfamethazine test.

N-acetyltransferase 2 (NAT2) catalyzes the bioactivation and/or detoxification of drugs and carcinogens. The aim of this study was to establish the correlation between the NAT2 genotype and the acetylating phenotype in a Mexican population using sulfamethazine as a probe. From a total of 122 individuals, 73 (59.8%) were slow and 49 (40.2%) were fast acetylators. Eleven individuals (9%) had the wild-type genotype (NAT2*4/NAT2*4). The most frequent genotype was NAT2*4/NAT2*5B observed in 20.66% of individuals. In conclusion, our results show that an accurate prediction of the acetylation phenotype by genotyping can be achieved in around half of the population. Further studies with a larger number of individuals are required to establish correlations between phenotype and genotype in half of that patients having a genotype combined with slow/rapid alleles.

Liver-selective expression of human arylamine N-acetyltransferase NAT2 in transgenic mice.

Human arylamine N-acetyltransferase 2 (NAT2) mediates the biotransformation of arylamine drugs and procarcinogens into either innocuous or reactive DNA-damaging metabolites and is expressed predominantly in liver. Interspecies differences and incongruous results between in vitro, in vivo, and epidemiological studies make it difficult to extrapolate animal results to human risk. We have generated human NAT2 transgenic mice on both C57BL/6 (hNAT2(tg)) and Nat1/2 null backgrounds [hNAT2(tg)Nat1/2(-/-)], in which liver-selective expression of human NAT2 is driven by the mouse albumin promoter. We detected expression of the human NAT2 transcript and protein in mouse liver by real-time PCR and Western blot analysis. NAT2 enzyme activity, measured using the human NAT2-selective substrate sulfamethazine (SMZ), was 40- to 80-fold higher in liver cytosols from hNAT2(tg)Nat1/2(-/-) mice than in wild-type mice. An unexpected gender difference was observed, with males displaying 2-fold higher activity than females. Transgenic mice also had an increased in vivo plasma clearance of SMZ and higher levels of N-acetylated SMZ than wild-type mice. Liver expression of human NAT2 did not affect the disposition of the human NAT1-selective substrate p-aminosalicylic acid (PAS), because hNAT2(tg)Nat1/2(-/-) mice displayed in vivo PAS pharmacokinetic profiles similar to those of Nat1/2(-/-) mice. The metabolism of 4-aminobiphenyl was similar between hNAT2(tg)Nat1/2(-/-) and wild-type mice with the exception of a more liver-restricted pattern in hNAT2(tg)Nat1/2(-/-) mice and lower activity in females. Overall, the hNAT2(tg)Nat1/2(-/-) mouse mimics human expression of NAT2 and may thus be of value in clarifying the role of human NAT2 in arylamine clearance, detoxification, and bioactivation.

A physiologically based pharmacokinetic model linking plasma protein binding interactions with drug disposition.

Combination drug therapy increases the chance for an adverse drug reactions due to drug-drug interactions. Altered disposition for sulfamethazine (SMZ) when concurrently administered with flunixin meglumine (FLU) in swine could lead to increased tissue residues. There is a need for a pharmacokinetic modeling technique that can predict the consequences of possible drug interactions. A physiologically based pharmacokinetic model was developed that links plasma protein binding interactions to drug disposition for SMZ and FLU in swine. The model predicted a sustained decrease in total drug and a temporary increase in free drug concentration. An in vivo study confirmed the presence of a drug interaction. Neither the model nor the in vivo study revealed clinically significant changes that alter tissue disposition. This novel linkage approach has use in the prediction of the clinical impact of plasma protein binding interactions. Ultimately it could be used in the design of dosing regimens and in the protection of the food supply through prediction and minimization of tissue residues.

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).

Sulfamethazine water medication pharmacokinetics and contamination in a commercial pig production unit.

Sulfamethazine is often used to treat disease in the swine industry. Sulfamethazine is available as water or feed medication and historically (over the past 40 years) has been associated with residue violations in both the United States and Europe. Despite sulfamethazine's approval for use as a water medication, little research on the pharmacokinetics of the water formulation is available. Therefore, a pilot study was performed to determine the plasma levels of an approved sulfamethazine water medication. Plasma levels in pigs treated with an oral bolus (250 mg/kg), which is equivalent to the total drug consumed within a 24-h period, achieved therapeutic concentrations (50 microg/ml). Noncompartmental-based pharmacokinetic model parameters for clearance, half-life, and volume of distribution were consistent with previously published values in swine. However, the above treatment resulted in exposure of pen mates to sulfamethazine at levels currently above tolerance (0.1 ppm). Using a physiologically based pharmacokinetic model, the treatment dose simulation was compared with observed plasma levels of treated pigs. Flexibility of the physiologically based pharmacokinetic model also allowed simulation of control-pig plasma levels to estimate contamination exposure. A simulated exposure to 0.15 mg/kg twice within approximately 8 h resulted in detectable levels of sulfamethazine in the control pigs. After initial exposure, a much lower dose of 0.059 mg/kg maintained the contamination levels above tolerance for at least 3 days. These results are of concern for producers and veterinarians, because in commercial farms, the entire barn is often treated,and environmental contamination could result in residues of an unknown duration.

Sulfamethazine uptake by plants from manure-amended soil.

Animal manure is applied to agricultural land as a means to provide crop nutrients. However, animal manure often contains antibiotics as a result of extensive therapeutic and subtherapeutic use in livestock production. The objective of this study was to evaluate plant uptake of a sulfonamide-class antibiotic, sulfamethazine, in corn (Zea mays L.), lettuce (Lactuca sativa L.), and potato (Solanum tuberosum L.) grown in a manure-amended soil. The treatments were 0, 50, and 100 microg sulfamethazine mL(-1) manure applied at a rate of 56 000 L ha(-1). Results from the 45-d greenhouse experiment showed that sulfamethazine was taken up by all three crops, with concentrations in plant tissue ranging from 0.1 to 1.2 mg kg(-1) dry weight. Sulfamethazine concentrations in plant tissue increased with corresponding increase of sulfamethazine in manure. Highest plant tissue concentrations were found in corn and lettuce, followed by potato. Total accumulation of sulfamethazine in plant tissue after 45 d of growth was less than 0.1% of the amount applied to soil in manure. These results raise potential human health concerns of consuming low levels of antibiotics from produce grown on manure-amended soils.

A sulfadimidine model to evaluate pharmacokinetics and residues at various concentrations in laying hen.

Low level intake of drugs from the ingestion of contaminated feed may lead to residue problems in food animals. Sulfadimidine (SDD) was used as a model to determine the residue risk at various doses in laying hens. The drug was administered as a single intravenous injection (100 mg kg(-1) body weight, BW), as a single oral dose (100, 30, 10, 3, 1 mg kg(-1) BW) and via medicated feed for 7 consecutive days (30, 10, 3 mg kg(-1) BW). Drug levels were determined with HPLC-UV for plasma, yolk and albumen. Pharmacokinetic values, which were calculated using a first-order one-compartment model, residue levels and transfer rates into the eggs were found to be dose-dependent. Even low doses of 3 and 1 mg kg(-1) BW resulted in measurable residues in yolk and albumen 1 day after a single oral administration. After ingestion of medicated feed at 3 mg kg(-1) BW, mean drug levels at 0.14 +/- 0.01 microg g(-1) were found in albumen and at 0.09 +/- 0.01 microg ml(-1) in plasma. Generally, the residue levels in albumen and plasma were higher than in yolk. These findings demonstrate a residue risk for the consumer even after low level intake of drugs.