Immunochemical detection of aminoglycosides in milk and kidney

In 1996, the European Union established provisional maximum residue limits (MRL) for gentamicin, neomycin, streptomycin and dihydrostreptomycin in milk and tissue (0.1-5 mg kg-1). For the detection of these four aminoglycosides, three enzyme linked immunosorbent assays (ELISA) for applications in milk and kidney were developed. The screening of defatted and diluted milk resulted in limits of determination (LDM) of < 0.01 mg l-1. Kidney samples were deproteinized with a trichloroacetic acid solution (3%) and after filtration and the addition of buffer, aliquots were used in the ELISA. The LDM of the four aminoglycosides in kidney were < 0.05 mg kg-1. The ELISA were found suitable for the semi-quantitative screening of milk and kidney for the presence of the four aminoglycosides far below the MRL levels. In randomly taken milk samples (n = 776) and in kidneys derived from healthy pigs (n = 124), the aminoglycoside residues found were far below their established MRL. In eight out of the 94 kidney samples obtained from diseased animals after emergency slaughter, aminoglycoside residues were above the MRL.

Suitability of the Charm HVS and a microbiological multiplate system for detection of residues in raw milk at EU maximum residue levels

In this paper we assessed the suitability of the Charm HVS and a newly developed microbiological multiplate system as post-screening tests to confirm the presence of residues in raw milk at or near the maximum permissible residue level (MRL). The multiplate system is composed of Bacillus stearothermophilus var. calidolactis plate at pH 8.0 for detection of beta-lactam antibiotics and tylosin, Bacillus cereus plate at pH 6.0 for detection of tetracyclines, Micrococcus luteus plate at pH 8.0 for detection of macrolides, Bacillus subtilis BGA plate at pH 8.0 for detection of aminoglycosides, trimethoprim-containing plate seeded with B. subtilis BGA at pH 7.0 for detection of sulphonamides, Escherichia coli plate at pH 6.0 for detection of quinolone and polymyxin, and Staphylococcus epidermidis plate at pH 6.0 for detection of novobiocin. For each test plate an action level is proposed in such a way that residues can be detected in raw bulk tank milk at levels near or below the established EU MRLs of beta-lactam antibiotics, tetracyclines, aminoglycosides, macrolides, sulphonamides, colistin, and quinolones. The Charm HVS test used to confirm the presence of tetracycline and macrolide residues gave false-positive results near the EU MRLs. The multiplate system gave valid results. Based on data for raw bulk tank milk samples and the proposed action level for each test plate for suspected samples, we demonstrated that the multiplate system is a reliable post-screening method that can be performed easily and cheaply in microbiological laboratories.

Testing of raw milk for tetracycline residues

A newly improved Bacillus calidolactis tube diffusion test and two postscreening test systems--a receptor assay (Charm HVS; Charm Sciences, Inc., Malden, MA) and a newly developed Bacillus cereus ATCC 11778 mycoides test system--were evaluated for the detection and identification of tetracycline residues using 973 samples of bulk milk taken at random in The Netherlands. All milk samples were assayed with the B. calidolactis tube and the receptor test. The milk samples testing as suspect or positive with one or both of the test systems were analyzed with HPLC (limit of detection, 10 ng/ml) and the recently developed B. cereus test system. The B. calidolactis tube diffusion test detected tetracycline residues > 45 ng/ml in milk. With the B. cereus test plate, residues of oxytetracycline and tetracycline of > 30 ng/ml milk were detected; for chlortetracycline and doxycycline, the detection limit was 10 ng/ml. Raw milk exhibiting inhibition diameters of < 20 mm on the B. cereus test plate fulfilled the European Union criterion for maximum residue level for tetracyclines of < 100 ng/ml (including their 4-epimer derivatives). The detection limits of the receptor assay depended on the type of milk used. The scintillation counts that were obtained for control samples of bulk milk were considerably lower than for the milks obtained from Charm Sciences, Inc. or processed using UHT pasteurization. One of 973 milk samples was suspect for tetracycline residues by means of the B. calidolactis tube test as well as by the receptor assay; 8 other samples were also considered to be positive using the receptor assay alone. The presence of tetracycline residues could not be proved for these 9 samples (residue concentration, < 10 ng/ml) with HPLC. We concluded that the receptor assay was not reliable to detect tetracycline residues in raw milk at < 150 ng/ml. The B. cereus test plate was determined to be an inexpensive, reliable alternative for the receptor assay for detection of tetracycline residues.

Bacterial inhibition tests used to screen for antimicrobial veterinary drug residues in slaughtered animals

Bacterial inhibition tests used to screen milk, tissues, blood, and urine for antimicrobial veterinary drug residues must be high volume, quick, rugged, inexpensive, and sensitive. Bacterial inhibition tests--such as the Swab Test on Premises (STOP), the Calf Antibiotic and Sulfa Test (CAST), the Fast Antibiotic Screen Test (FAST), the Charm Farm Test (CFT), the Antimicrobial Inhibition Monitor 96 (AIM-96) assay, the German Three Plate Test, the European Union Four Plate Test and the New Dutch Kidney Test--have been used to screen tissues for antimicrobial activity. The CFT and the Brilliant Black Reduction Test (BBRT) also have been used to screen plasma. The Live Animal Swab Test (LAST) was developed to screen urine. This review examines the use and limitations of these screening tests for regulatory control and avoidance of veterinary drug residues in meat. The ideal bacterial inhibition test for screening antimicrobial residues in slaughtered animals does not exist. Each of the current and potential tests has limitations.

Effects of sarafloxacin hydrochloride on human enteric bacteria under simulated human gut conditions

The effects of sarafloxacin, a newly developed veterinary fluoroquinolone antimicrobial, on 15 strains of aerobic and anaerobic bacteria of human origin were assessed under simulated human gut conditions. An in vitro gut simulation model was designed to mimic the situation of sarafloxacin (free and bound to meat) passing through the human gastrointestinal tract. The survival of bacteria in the simulation model and any subsequent change in the sensitivity of isolates to sarafloxacin were measured. The inhibitory level of sarafloxacin for the tested bacteria was strain dependent. It appeared that in broth culture Escherichia coli isolates were sensitive to sarafloxacin concentrations 5-fold lower than the concentrations present in the simulated gut model, suggesting that sarafloxacin may be partially unavailable due to absorption to organic matter in the model. There was no significant observed change in the sarafloxacin sensitivity of the bacterial strains exposed to the compound in the model.

Establishment of a microbiologically acceptable daily intake of antimicrobial drug residues

A model is presented to calculate the microbiologically acceptable daily intake (ADIm) of antibiotic residues in food products. The ADIm calculation is based on MIC values for indicator bacteria Escherichia coli, Bacteroides fragilis, Bifidobacterium spp. and Eubacterium spp., established under gut-like conditions in an in vitro simulation model. The maximum residue level (MRL) for residues in food products can be derived from the ADIm. Four phases can be distinguished in this gastro-intestinal simulation model, namely: 1. In vitro determination of the MIC for each bacterial strain by a standard method. 2. Incorporation of the drug into food (meat, milk) followed by testing of the stability of the antibiotic under gut-like conditions. 3. Adjustment of the 'gastric' fluid to the duodenal situation, inoculation with the test bacteria and anaerobic incubation at 37 degrees C for at least 18 h. 4. MIC reading confirmed by counting bacteria growing on specific solidified media. In this study the method for calculation of ADIm and MRL is given for flumequine as model drug. On the basis of MIC50 values for E. coli strains, a MRL for flumequine of 1.0 microgram/g meat or 0.25 microgram/ml milk was calculated. It is suggested that, depending on the antibacterial spectrum of the antibiotic involved, the ADIm can be determined with selected indicator bacteria, incubated under simulated gastrointestinal conditions.

Kanamycin concentrations in synovial fluid after intramuscular administration in the horse

Six adult ponies were injected in the same intramuscular site with kanamycin sulphate (10 mg/kg). Two hours later, arthrocenteses of the right metacarpophalangeal, radio-carpal, intercarpal, tibio-tarsal and metatarsophalangeal joints were performed within 3 minutes. Arthrocenteses of the same joints on the left side were conducted 5 hours later. When expressed as a percentage of plasma drug concentration, differences in synovial fluid drug concentration between the joints sampled at 2 and 5 hours after injection were not detected.

Pharmacokinetics in immature animals: a review

Differences in drug pharmacokinetics between newborn and adult mammals are reviewed. The pharmacokinetic alterations during the maturation process are related to changes in the pattern of absorption, distribution, metabolism, and renal excretion. The most pronounced feature in neonates vs adults is the prolonged elimination half-life of drugs. The main factors causing delayed elimination are under-developed renal clearance and immature metabolism of drugs. Special attention has to be paid to central nervous system depressants and to drugs that are extensively metabolized because they will accumulate with repeated dosing of newborn animals.

Direct-gradient high-performance liquid chromatographic analysis and preliminary pharmacokinetics of flumequine and flumequine acyl glucuronide in humans: effect of probenecid

A gradient high-performance liquid chromatographic analysis for the direct measurement of flumequine, with its acyl glucuronide, in plasma and urine of humans has been developed. In order to prevent hydrolysis and isomerization of flumequine acyl glucuronide, the samples were acidified by the oral intake of four 1.2-g amounts of ammonium chloride per day. In contrast to the acyl glucuronides of non-steroidal anti-inflammatory drugs, flumequine and its acyl glucuronide were stable in urine of pH 5.0-8.0. Flumequine acyl glucuronide is unstable at pH 1.5. In acidic urine (pH 5-6), almost no flumequine is excreted unchanged (1%): it is excreted chiefly as acyl glucuronide (84.2%). Probenecid co-medication reduces the renal excretion rate of flumequine acyl glucuronide from 662 to 447 micrograms/min (p = 0.00080), but not the percentage of glucuronidation.

[How can the incidence of antibiotic residues in meat animals be minimized?]

The causes of the presence of antibiotic residues in slaughtered animals are analysed. The fact is stressed that the persistence of antibiotic residues in slaughtered animals varies, among other things, with the antibiotic itself, the pharmaceutical design and, in the case of subcutaneous or intramuscular injection, the site of injection and the severity of local irritation of the tissues. There are marked differences between the various antibiotic products as regards the local irritation induced and the residual persistence in organs at the site of injection. A selective use of antibiotics and forms of administration (so-called 'positive list') is advocated, by which the incidence of antibiotic residues in slaughtered animals can be restricted. Recommendations for drawing up a 'positive' list' are made.

Pharmacokinetics of a sulphamethoxazole/trimethoprim formulation in pigs after intravenous administration

Plasma disposition, metabolism, protein binding and renal clearance of sulphamethoxazole (SMZ) and trimethoprim (TMP) were studied in four pigs after intravenous administration at a dose of 40 and 8 mg/kg, respectively. SMZ and TMP were quickly eliminated (mean elimination half-lives: 2.7 and 2.4 h, respectively). SMZ was predominantly acetylated; no hydroxy and glucuronide derivates could be detected in plasma and urine. TMP was 0-demethylated into 4-hydroxytrimethoprim (M1) and 3-hydroxytrimethoprim (M4) metabolite and subsequently extensively glucuronidated. SMZ, TMP and its M1 metabolite were excreted predominantly by glomerular filtration, while N4-acetylsulphamethoxazole and glucuronide conjugates of the M1 and M4 metabolites of TMP were actively eliminated by tubular secretion. The proportional drug percentage being present in the urine as parent compound was 13.1% for TMP and 16.0% for SMZ. The glucuronide conjugates of the M1 and M4 metabolites formed the main part (81.5%) of urinary TMP excretion pattern.

Slaughter pigs and pork as a source of human pathogenic Yersinia enterocolitica

Pathogenic Yersinia enterocolitica strains (serogroups 0:3;0:9 and 0:5.27) were isolated from 36 (42%) of 86 porcine tonsils, 8 (20%) of 40 tongues, 17 (17%) of 100 rectal swabs and from 4 (1%) of 400 pork samples. Pathogenic Yersinia strains were not isolated from samples of 210 pig carcasses and from 20 samples of porcine head meat. These results confirm that pigs are an important reservoir of pathogenic Y. enterocolitica. However, contamination of carcasses during the slaughtering process with Yersinia from either faecal material or from the tonsillary region does not seem to occur frequently and this may also explain the low contamination rate of pathogenic Y. enterocolitica found for pork. For the isolation of pathogenic Y. enterocolitica strains from foods, enrichment in irgasan-ticarcillin-chlorate broth (ITC) and isolation on SS-deoxycholate-calcium agar (SSDC) is recommended.

Pharmacokinetics of sulphadimidine in carp (Cyprinus carpio L.) and rainbow trout (Salmo gairdneri Richardson) acclimated at two different temperature levels

The influence of temperature (10 degrees C and 20 degrees C) on pharmacokinetics and metabolism of sulphadimidine (SDM) in carp and trout was studied. At 20 degrees C a significantly lower level of distribution (Vdarea) and a significantly shorter elimination half-life (T(1/2)beta) was achieved in both species compared to the 10 degrees C level. In carp the body clearance parameter (ClB(SDM)) was significantly higher at 20 degrees C compared to the value at 10 degrees C, whereas for trout this parameter was in the same order of magnitude for both temperatures. N4-acetylsulphadimidine (N4-SDM) was the main metabolite of SDM in both species at the two temperature levels. The relative N4-SDM plasma percentage in carp was significantly higher at 20 degrees C than at 10 degrees C, whereas there was in trout no significant difference. In neither species was the peak plasma concentration of N4-SDM (Cmax(N4-SDM)) significantly different at two temperatures. The corresponding peak time of this metabolite (Tmax(N4-SDM)) was significantly shorter at 20 degrees C compared to 10 degrees C in both carp and trout. In carp at both temperatures, acetylation occurs to a greater extent than hydroxylation. Only the 6-hydroxymethyl-metabolite (SCH2OH) was detected in carp, at a significant different level at the two temperatures. Concentrations of hydroxy metabolites in trout were at the detection level of the HPLC-method (0.02-micrograms/ml). The glucuronide metabolite (SOH-gluc.) was not detected in either species at the two temperatures.

[Pork meat as a source of pathogenic Yersinia enterocolitica]

During a period of eight months, samples of carcasses, tonsils, tongues and rectal swabs were taken in four pig slaughter halls. Porcine head meat was sampled in a meat products factory and samples of minced pork were taken in butcher's shops. Pathogenic strains of Yersinia enterocolitica (serological groups O:3, O:9 and O:5.27) were isolated from 36 (42 per cent) of 86 porcine tonsils, 8 (20 per cent) of 40 tongues, 17 (17 per cent) of 100 rectal swabs and from 4 (1 per cent) of 400 pork samples. Pathogenic strains of Yersinia were not isolated from samples of 210 pig carcasses and from 20 samples of porcine head meat. These results confirm that pigs are an important reservoir of pathogenic Y. enterocolitica. However, contamination of carcasses during the process of slaughter with Yersinia from either faecal material or from the tonsillary region does not seem to occur frequently, which may also explain the low rate of contamination with pathogenic Y. enterocolitica observed in pork. As pork is rarely contaminated with pathogenic Y. enterocolitica, the possibilities for growth of these organisms in raw pork are limited, the minimum infective dose is probably high and pork is usually not eaten raw, it is not likely that pork is an important source of yersiniosis in the Netherlands.

Pharmacokinetics of sulphamethoxazole in calves and cows

The kinetics of sulphamethoxazole (SMZ) in plasma and milk, and its metabolism, protein binding and renal clearance were studied in three newborn calves and two dairy cows after intravenous administration. SMZ was predominantly acetylated; no hydroxy and glucuronide derivatives could be detected in plasma and urine. Age-dependent pharmacokinetics and metabolism of SMZ were observed. The plasma concentration-time curves of the N4-acetyl metabolite in the elimination phase were parallel to those of the parent drug; the N4-acetyl metabolite plasma percentage depended on age and ranged between 100% (new-born) to 24.5% (cow). SMZ was rapidly eliminated (elimination half-lives: 2.0-4.7 h) and exhibited a relatively small distribution volume (VDarea: 0.44-0.57 l/kg). SMZ was excreted predominantly by glomerular filtration, while its N4-acetyl metabolite was actively eliminated by tubular secretion.

A comparative study on irritation and residue aspects of five oxytetracycline formulations administered intramuscularly to calves, pigs and sheep

After intramuscular (IM) administration (dose 20 mg/kg) of three 20% (Terramycin/LA (product A), Alamycin LA (product B) and Terralon 20% LA (product C) and two 10% oxytetracycline (OTC) formulations (Engemycin 10% (product D) and Oxyject 10% (product E)), to calves, pigs and sheep, the OTC residue concentrations were determined in organs, muscle, fat, plasma, urine and at the injection sites at 10 days post injection (p.i.). At that time the irritation at the injection site was studied, too. The three 20%-formulations (products A, B, C) and one 10%-formulation (product E) induced considerable local irritation in and between the muscles. This was most pronounced in calves and pigs; in sheep the extent of irritation was limited. Ten days after administration of formulations A, B, C and E, OTC residues were found in organs and the OTC recovery at the injection sites varied widely among the three species. Following IM injection of product D minimal tissue irritation and no OTC residues could be detected at the injection site at 10 days p.i. The differences in local tissue irritation and the residue state of the carcass (including injection site) are related to the various solvent systems used in the formulations.

The effect of phenylbutazone on the plasma disposition of penicillin G in the horse

A pilot study in two ponies showed that the plasma concentrations of intramuscularly administered procaine penicillin were higher if phenylbutazone was administered concurrently. In two other trials, each involving five horses, intravenous sodium penicillin was administered with and without concurrent intravenously injected phenylbutazone, and procaine penicillin was injected intramuscularly with and without oral phenylbutazone. In both cases the plasma concentrations of penicillin were higher when phenylbutazone was given. The pharmacokinetic parameters indicated that the effect was probably due to a lower peripheral distribution because the penetration of penicillin into the tissues was greatly reduced.

Age-dependent pharmacokinetics of phenylbutazone in calves

The pharmacokinetics of phenylbutazone (PBZ) in relation to age was studied in calves. The drug was applied intravenously to calves (dose 22 mg/kg), which were divided, depending on age, into three groups. Heparinised blood samples were taken in defined intervals. The concentrations of phenylbutazone and two of its metabolites were determined in plasma by high performance liquid chromatography. The pharmacokinetic data derived from 1-month-old calves revealed a longer persistence (elimination half-lives twice as long, total body clearance 40-50% lower) of PBZ in the body than in the other two groups of calves aged 3-6 months. With respect to the long elimination half-lives (mean values 39-94 h), caution is needed in case of repeated doses (accumulation).

Postmortal degradation of furazolidone and furaltadone in edible tissues of calves

Rapid and complete postmortal degradation of furazolidone and furaltadone occurred in liver, kidney and muscle tissues of veal calves. Different degradation half-lives were observed between these tissues, the mean ranging from less than 7 minutes to 63 minutes. At 24 h after slaughter the parent nitrofurans were no longer detectable in edible tissues. For residue monitoring purposes plasma and/or urine can be used, if these matrices are treated in a specific way immediately after slaughter; muscle tissues and organs are unsuitable for residue monitoring of parent nitrofurans.

Oxidation and O-dealkylation of sulphamonomethoxine by the turtle Pseudemys scripta elegans

Sulphamonomethoxine is O-demethylated at the 6 position and oxidised at the 2 position of the pyrimidine substituent by Pseudemys scripta elegans. No N4-acetylation takes place. The yield of the oxidation reaction is twice that of the O-demethylation reaction.

O-demethylation and N4-acetylation of sulphadimethoxine by the turtle Pseudemys scripta elegans

After an oral dose of 350 mg of sulphadimethoxine, the turtle Pseudemys scripta elegans O-dealkylates sulphadimethoxine at the 2- and 6-position at 38% and 19% respectively, the 2-position being favoured. Acetylation of sulphadimethoxine and its hydroxy metabolites occurs for 57.4%.

Comparative pharmacokinetics of oxytetracycline in rainbow trout (Salmo gairdneri) and African catfish (Clarias gariepinus)

A comparative pharmacokinetic study was conducted in rainbow trout (Salmo gairdneri) and African catfish (Clarias gariepinus) following intravenous (i.v.) and intramuscular (i.m.) administration of oxytetracycline (OTC) at a dose rate of 60 mg/kg body weight. Trout and catfish were kept in aerated tap water in tanks at constant temperatures of 12 degrees C and 25 degrees C, respectively. The two- and three-compartment open models adequately described plasma drug disposition in African catfish and rainbow trout respectively, following i.v. OTC administration. Compared to catfish (COP = 86 +/- 10 micrograms/ml) an eightfold higher extrapolated zero time concentration was obtained in trout (COP = 753 +/- 290 micrograms/ml). A significant difference was observed with respect to the relatively large apparent distribution volumes (Vd(area] after i.v. OTC administration (trout, mean value: 2.1 l/kg; catfish, mean value: 1.3 l/kg). The mean final elimination half-lives of both fish species were greater than previously reported in mammals (trout, 89.5 h; catfish, 80.3 h). A mean maximum plasma concentration (Cmax = 56.9 micrograms/ml) was obtained in trout at 4 h after i.m. administration of OTC. In catfish a lower Cmax of 43.4 micrograms/ml was determined at about 7 h. No significant difference was observed with respect to bioavailability following i.m. administration of OTC (trout, 85%; catfish, 86%).

Pharmacokinetics and renal clearance of sulphadimidine, sulphamerazine and sulphadiazine and their N4-acetyl and hydroxy metabolites in pigs

The effect of molecular structure on the drug disposition and protein binding in plasma, the urinary recovery, and the renal clearance of sulphamerazine (SMR), sulphadiazine (SDZ), and sulphadimidine (SDM) and their N4-acetyl and hydroxy derivatives were studied in pigs. Following IV administration of SDM, SMR and SDZ, their mean elimination half-lives were 12.4 h, 4.3 h and 4.9 h respectively. The plasma concentrations of parent sulphonamide were higher than those of the metabolites, and ran parallel. The acetylated derivatives were the main metabolites; traces of 6-hydroxymethylsulphamerazine and 4-hydroxysulphadiazine were detected in plasma. The urine recovery data showed that in pigs acetylation is the major elimination pathway of SDM, SMR and SDZ; hydroxylation became more important in case of SMR (6-hydroxymethyl and 4-hydroxy derivatives) and SDZ (4-hydroxy derivatives) than in SDM. In pigs methyl substitution of the pyrimidine side chain decreased the renal clearance of the parent drug and made the parent compound less accessible for hydroxylation. Acetylation and hydroxylation speeded up drug elimination, because their renal clearance values were higher than those of the parent drug.

N-oxidation, O-demethylation, and excretion of trimethoprim by the turtle Pseudemys scripta elegans

Trimethoprim was excreted within one hour after being given orally to the turtle Pseudemys scripta elegans. No O-demethylated or N-oxide metabolites were detected.

O-demethylation and N4-acetylation of sulfadimethoxine by the snail Cepaea hortensis

The snail Cepaea hortensis O-dealkylates sulfadimethoxine at the 2- and 6-position, the 2-position being favoured. Sulfadimethoxine is also acetylated, while no measurable acetylation of the hydroxy (= demethyl) metabolites took place.

Oxidation and acetylation of sulfamonomethoxine by the snail Cepaea hortensis

Sulfamonomethoxine is not O-demethylated in the snail Cepaea hortensis, but acetylated (15.2%) and oxidised (0.78%) at the 2 position of the pyrimidine nucleus.

Pharmacokinetics and metabolism of sulphadimidine in kids at 12 and 18 weeks of age

The pharmacokinetics and metabolism of sulphadimidine (SDM) following intravenous administration of 100 mg/kg were studied in seven dwarf preruminant kids at 12 weeks of age, and again at the ruminant stage, when the animals were 18 weeks old. The persistence of SDM in 18-week-old kids was prolonged in comparison to the 12-week-old animals: a lower total body clearance and a prolonged elimination of SDM were obtained in the older animals. The renal clearance values of SDM and its metabolites were the same at both ages. The decrease of SDM clearance is related to the significant reduction in SDM hydroxylation at the older age. The reduced oxidative hepatic metabolism may result from the sexual maturation of the kids.

Pharmacokinetics, metabolism and renal clearance of sulphatroxazole in calves and cows

The pharmacokinetic analysis of plasma concentration--time curves after a single i.v. dose of 20 mg/kg sulphatroxazole (STZ) to calves and cows revealed a small distribution volume of STZ (mean VD(area) = 0.22-0.26 l/kg) and an age dependent elimination (mean t1/2 6.6-18.8 h). In calves and cows, STZ was extensively metabolized into the N4-acetyl and 5-hydroxy derivatives. In the plasma of calves, the N4-acetyl metabolite (N4-STZ) was present in greater amounts than the hydroxy metabolite (5-OH-STZ), while in cows' plasma concentration of these two metabolites were similar. In the milk of dairy cows STZ concentrations paralleled those of the metabolites and were approximately 21 times lower than corresponding plasma concentrations. The mean plasma protein binding of STZ and its metabolites ranged from 36.4 to 82.5% of total concentration. The N4-STZ derivative was excreted by tubular secretion; the 5-OH-STZ and the parent compound, mainly by glomerular filtration. In calves the majority of STZ administered was excreted as N4-STZ (40-52%), while in cows the parent drug dominated the urinary excretion (36%).

Effect of tick-borne fever (Ehrlichia phagocytophila) and trypanosomiasis (Trypanosoma brucei 1066) on the pharmacokinetics of sulfadimidine and its metabolites in goats

The effect of tick-borne fever (TBF) and trypanosomiasis (TBR) on the plasma disposition of sulfadimidine (SDD) in goats was studied after iv administration of 20 and 200 mg/kg of body weight. In each group of six goats, the plasma disappearance curves showed four animals with rapid and two with slow SDD elimination. It is likely that this difference is determined by oxidative rather than acetylation phenotype. In all goats administered 20 mg/kg, half-life increased with TBF but not with TBR. Vd(beta) decreased with both infections. With 200 mg/kg, Vd did not change, whereas AUC and MRT increased with both infections. Metabolites were examined in TBF experiments: N4-acetyl-SDD (N4Ac), 6-hydroxymethyl-SDD (CH2OH) and its glucuronide, 5-hydroxy-SDD (SOH) and its glucuronide, and 6-carboxy-SDD (COOH) and its glucuronide (COOH-glu). At low dose (20 mg/kg), TBF caused the proportion of dose recovered from urine as unchanged SDD to be halved, whereas N4Ac increased correspondingly (2x). After the high dose (200 mg/kg), elimination was saturated and changes in proportional recovery of SDD in urine were less. However, the N4Ac proportion was still doubled, in contrast to the other metabolites, suggesting that saturation was caused by oxidations rather than by acetylation. Formation of CH2OH was the same in health and disease after the low dose, but glucuronidation dropped from 20% to 4% (rapid) or 7% (slow) of total CH2OH.(ABSTRACT TRUNCATED AT 250 WORDS)

Excretion and metabolism of a series of xanthines by the turtle Pseudemys scripta elegans

The xanthines paraxanthine, xanthine, and uric acid are absorbed completely by the turtle Pseudemys scripta elegans and metabolised presumably into CO2 and NH3. No intermediate metabolites are excreted. Caffeine, hydroxycaffein, theobromine, hydroxytheobromine, and hydroxypraxanthine are absorbed and excreted in different amounts or percentages of the dose administered. Intermediate metabolites of these compounds are not excreted. The turtle Pseudemys scripta elegans may, therefore, be ammonotelic.

N-oxidation, N-demethylation, and excretion of pefloxacin by the turtle Pseudemys scripta elegans

Pefloxacin is minimally absorbed by the gastrointestinal tract of the turtle Pseudemys scripta elegans and then N-oxidised and N-demethylated. Pefloxacin is excreted within one hour after being given orally to the turtles.

Monitoring milk for chloramphenicol residues by an immunoassay (Quik-card)

An easy to perform immunoassay method (Quik-card) for monitoring milk on the presence of chloramphenicol residues exceeding 5 to 10 ppb is described, as well as an extraction and preconcentration method utilising a Sep-pak silica cartridge, which enables the detection of CAP residues in milk in concentrations exceeding 1 ppb by HPLC and 0.1 ppb by the immunoassay.

Pharmacokinetics, renal clearance and metabolism of ciprofloxacin following intravenous and oral administration to calves and pigs

The pharmacokinetics of ciprofloxacin, a quinoline derivative with marked bactericidal activity against gram-negative bacteria, was studied in calves and pigs following intravenous and oral administration. Ciprofloxacin was rapidly and well distributed in the body, exhibited a short elimination half-life of 2.5 h in both species, and was rapidly absorbed after oral administration (Tmax:2 to 3 h). The oral bioavailability in calves was 53 +/- 14% and for 1 pig 37.3%. The renal clearance of the unbound ciprofloxacin for both species was of the same order, indicated a predominantly tubular secretion pattern, and accounted for about 46% of the total drug elimination. No complete drug mass balance could be demonstrated. Small amounts of two metabolites were detected in the urine of calves, but not in pig urine.

Pharmacokinetics of ciprofloxacin in carp, African catfish and rainbow trout

The plasma disposition of ciprofloxacin was studied in carp, African catfish and trout after intravenous (IV) and intramuscular (IM) administration at a dose rate of 15 mg/kg. Pharmacokinetic analysis of IV data showed that ciprofloxacin was well distributed (distribution volume Vd(area): 3.08-5.59 litre/kg) and exhibited a similar elimination half-life of about 14 h in these 3 fish species. After IM administration to carp and trout a rapid absorption was noticed; the maximum ciprofloxacin plasma concentrations (mean: 3.49 and 2.37 micrograms/ml, respectively), were achieved within 1 h after injection. At the dose level applied, ciprofloxacin has potential therapeutic value for 2-5 days especially against gram-negative bacterial fish pathogens.

Pharmacokinetics, metabolism, and renal clearance of sulfadiazine, sulfamerazine, and sulfamethazine and of their N4-acetyl and hydroxy metabolites in calves and cows

The effect of molecular structure on the drug disposition and protein binding in plasma and milk, the urinary recovery, and the renal clearance of sulfadiazine, sulfamerazine, and sulfamethazine and of their N4-acetyl and hydroxy derivatives were studied in calves and cows. Sulfadiazine was highly acetylated and was slightly hydroxylated. Sulfamerazine and sulfamethazine were hydroxylated predominantly at the methyl group of the pyrimidine side chain; hydroxylation of the pyrimidine ring itself was more extensive for sulfamethazine than for sulfamerazine. At dosages between 100 and 200 mg/kg of body weight, sulfamethazine had a capacity-limited elimination pattern, which was not observed for sulfadiazine or sulfamerazine. The concentrations of the parent sulfonamide and its metabolites in plasma and milk were parallel, the latter being lower. Metabolite concentrations in milk were at least 8 times lower than those of the parent drug. Metabolism speeds drug elimination, producing compounds with renal clearance values higher than those of the parent drug. The effect on the metabolism and renal clearance of methyl substitution in the pyrimidine side chain is discussed.

The effect of testosterone and rutting on the metabolism and pharmacokinetics of sulphadimidine in goats

After testosterone pretreatment of castrated goats and during the rutting season of adult entire male goats, the oxidative metabolism of sulphadimidine (SDM) was inhibited markedly compared with the castrated control state of these animals. The oxidation of the 5 position (yielding 5-hydroxysulphadimidine) and of the 6-hydroxymethyl group (yielding 6-carboxysulphadimidine) was decreased equally, with that of the methyl group at the pyrimidine side chain itself being 6-hydroxymethylsulphadimidine (CH2OH), whereas the acetylation pathway was unaffected by testosterone. The consequence of altered metabolism by testosterone was a prolongation of SDM presence in the body. Effects on protein binding of the CH2OH metabolite and on the renal clearance of SDM were also investigated.

[The New Dutch Kidney Test. III. Practical evaluation]

The New Netherlands Kidney Test (NNKT) is a method used to detect residues of antibacterial agents in slaughtered animals. This test will shortly be substituted for the current Netherlands Kidney Test (NKT). The new method was tested for its suitability in meat inspection in the field by four district laboratories, comparative studies with the current Netherlands Kidney test being done at the same time. These investigations showed that, when the new test (NNKT) was used, 5.3 per cent of the category of diseased animals and, using the current Netherlands Kidney Test, 2.2 per cent of these animals were positive. When control discs were used, it was shown that reproducibility of the new test (NNKT) within and between the participating laboratories was satisfactory. A method was developed to obtain similar results on re-examination with the NNKT as those obtained in the first inspection. By freezing the duplicate discs at the time of performance of the test and using these discs for re-inspection, reproducible results were obtained with the NNKT. The substance inhibiting the growth of bacteria was identified in a number of specimens diagnosed as positive when the NNKT was used. False-positive results were not recorded in the NNKT.

[The New Dutch Kidney Test. II. Sensitivity of the test system]

When the in vitro sensitivity of the New Netherlands Kidney Test (NNKT) is compared with that of the test plates of the current Netherlands Kidney Test (NKT) and the EEC four-plate system (ECT), this shows that it occupies a middle position with regard to aminoglycosides, macrolides and tetracyclines. The test plate of the NNKT is more sensitive to sulphonamides. Experimental qualitative and quantitative studies in slaughtered pigs showed that the New Netherlands Kidney Test was equally sensitive or more so in detecting residues of sulphonamides, chloramphenicol, tetracyclines, aminoglycosides and penicillin derivatives than the ECT system for meat. In addition to the simplicity of the current Netherlands Kidney Test, the New Netherlands Kidney Test also shows the broad-spectrum sensitivity of the ECT system. When tolerance standard of nitrofurans or chloramphenicol respectively is 1 or 10 ppb, the New Netherlands Kidney Test will fail.

Effect of induced synovial inflammation on pharmacokinetics and synovial concentration of sodium ampicillin and kanamycin sulfate after systemic administration in ponies

Single doses of sodium ampicillin (10 mg/kg) and kanamycin sulfate (5 mg/kg) were administered intramuscularly (i.m.) separately, and then together, to five pony mares. The plasma antibiotic concentration-time curves were constructed. The pharmacokinetic parameters of the antibiotics given separately were not altered by concurrent administration. Four of the five pony mares were then given the i.m. kanamycin/ampicillin combination 4 h after acute synovitis and fever had been induced by injection of lipopolysaccharide into the left intercarpal joint. The plasma concentration-time curves and the synovial concentration-time curves of inflamed and normal joints were constructed. The Cmax of ampicillin in the lipopolysaccharide experiment was significantly higher than in the other experiments. The antibiotics entered the synovial fluid of the inflamed joints more quickly and attained higher concentrations than in the uninflamed joints. The ampicillin concentration exceeded 5 micrograms/ml in inflamed synovial fluid for some 2.5 h after injection, and kanamycin sulfate concentration exceeded 2 micrograms/ml for 7 h.

[The New Dutch Kidney Test. I. Description of the method]

The New Netherlands Kidney test is designed for the detection of antibacterial residues in slaughtered animals. It is a single-plate system in which the culture medium used is composed of Standard II nutrient agar, supplemented with 1 per cent of NaCl, 1 per cent of dextrose, 0.2 per cent of KH2PO4 and 0.28 per cent of Na2HPO4.12H2O. After autoclaving, this medium is cooled to 55 degrees C, which is followed by the addition of trimethoprim (0.12 microgram/ml of agar) and spores of Bacillus subtilis BGA (10(4) ml of agar). The pH should be adjusted to 7.00 +/- 0.05, the prepared medium then being poured out into plates specially designed for this purpose, in such a manner that the thickness of the layer of agar is 2.2 mm throughout. The following method is used in examining slaughtered animals for the presence of residues showing antibacterial activity. Four paper discs are placed in the renal pelvis for a minimum period of thirty minutes; two discs impregnated with fluid from the renal pelvis are frozen at -20 degrees C for possible re-inspection and the other two are laid diagonally on a test plate. 25 microliter of a trimethoprim solution (containing 2 micrograms of TMP per ml of a 10 per cent NaCl solution) are dropped on each of the two last-named discs. The test plates are incubated at 37 degrees C for a period ranging from thirteen to eighteen hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma disposition and renal clearance of sulphadimidine and its metabolites in laying hens

Plasma disposition of sulphadimidine (SDM) and its metabolites was studied in laying hens after 100 mg SDM kg-1 doses were administered as a single intravenous dose, a single oral dose and multiple oral doses once daily for five consecutive days. SDM was extensively metabolised by acetylation and hydroxylation. In plasma, the metabolite observed with the highest concentration was N4-acetylsulphadimidine (N4-SDM) followed by hydroxymethylsulphadimidine (CH2OH) and 5-hydroxysulphadimidine. Following intravenous administration a biphasic elimination (as seen for a capacity limited reaction) pattern for SDM and its metabolites was observed. Multiple (5x) SDM dosing revealed plasma SDM concentrations ranging between 7 and 108 micrograms ml-1; within 96 hours of termination of the multiple SDM dosing, the plasma SDM concentration was below 0.01 micrograms ml-1. The renal clearances of N4-SDM and the hydroxy metabolites were approximately 10 times greater than that of SDM. The SDM mass balance (faecal/urinary recovery) showed a loss of 56 per cent after intravenous dosage and of 67 per cent after a single oral dosage; the hydroxy metabolites accounted for the highest percentage in faeces/urine. Thus additional metabolic pathways must exist in laying hens.

[The predictive value of urinalysis in the New Dutch Kidney Test]

A urine test is described, by which a reliable indication of the time of slaughter is obtained in normal as well as in diseased animals, in which the New Netherlands Kidney Test (NNKT) will be negative. The test plate and testing procedure of the NNKT are used in this urine test.