Hydroxylation and oxidation of nalidixic acid in the turtle Pseudemys scripta elegans

The turtle Pseudemys scripta elegans hydroxylates nalidixic acid into 7-hydroxynalidixic acid; this latter metabolite is oxidised into 7-carboxynalidixic acid. The elimination half-life of nalidixic acid in the turtle is 30 h. No glucuronides of nalidixic- and 7-hydroxynalidixic acid are formed, as they are in man.

[Waiting periods in the New Netherlands Kidney Test]

The New Netherlands Kidney Test used in monitoring slaughtered animals for antimicrobial residues will be legalised in the near future. With regard to this new test, minimum pre-slaughter withdrawal periods required to obtain negative results of the test are roughly indicated. The problem of establishing reliable withdrawal periods is briefly discussed.

Acetylation, deacetylation and hydroxylation of sulphamethoxazole and N4-acetylsulphamethoxazole in the turtle Pseudemys scripta elegans

The turtle Pseudemys scripta elegans is able to hydroxylate and acetylate Sulphamethoxazole in a way that is comparable to man, i.e. the rate and yield of hydroxylation equals that of the acetylation. The hydroxy metabolites 5-hydroxy- and N4-acetyl-5-hydroxysulphamethoxazole are not glucuronidated. N4-acetylsulphamethoxazole is neither deacetylated nor hydroxylated.

Acetylation, deacetylation and hydroxylation of sulphamethoxazole and N4-acetylsulphamethoxazole in the snail Cepaea hortensis

The snail Cepaea hortensis is able to acetylate and hydroxylate sulphamethoxazole in a similar way to man. About one percent deacetylation, but no hydroxylation of N4-acetysulphamethoxazole takes place. The relative rates of the metabolic pathways for hydroxylation and acetylation of sulphamethoxazole are equal.

Some pharmacokinetic data about furaltadone and nitrofurazone administered orally to preruminant calves

A single oral dosage of furaltadone and nitrofurazone (14.0 mg/kg) to 5 preruminant calves (in a cross-over trial) revealed mean maximum plasma concentration of 2.5 and 3.5 microgram/ml, respectively, at approximately 3 h after administration. The final elimination half-lives of furaltadone and nitrofurazone were 2.5 and 5 h, respectively. Urinary recovery of these two nitrofurans in 3 calves revealed approximately 2% of the orally administered dose. The renal clearance of the unbound drugs did not differ (for both drugs approximately 0.42 ml/min/kg); furaltadone clearance was strongly related to urine flow.

[Reconsideration of the 'bacteriological examination' of slaughter stock]

A comparative trial was made by six meat inspection services to attain uniform indications for the 'Bacteriological Examination' of slaughtered animals in accordance with the 'Meat Inspection Regulations' of the Dutch 'Meat Inspection Act'. The results of the study compelled the investigators to scrutinize these regulations. The 'Bacteriological Examination' which is prescribed, is designed to exclude septicaemic animals from human consumption. Applying the rules will result in condemnation of animals harbouring a small number of bacteria which have a minimum significance for the health of consumers, whereas animals harbouring organisms potentially pathogenic for man are overlooked. It is concluded that the 'Meat Inspection Regulations' should be considered.

The effect of tick-borne fever on metabolism and renal clearance of sulfadimidine in goats

The tick-borne fever (TBF) model was used to study the effect of fever on the metabolism of sulfadimidine in goats. During TBF the elimination half-lives were prolonged, and the renal clearance values of sulfadimidine and the majority of its metabolites were markedly diminished compared with those in the uninfected state. During TBF the steady-state levels of the hydroxy metabolites were markedly increased. TBF reduced the extent of hydroxymethylation of the pyrimidine side chain; TBF did not affect acetylation of sulfadimidine. In one goat a progressive accumulation of the metabolites was noticed.

Pharmacokinetics of sulphanilamide and its three acetyl metabolites in dairy cows and calves

An intravenous low dosage of sulphanilamide (SAA) (14.0 mg/kg) to 6 pre-ruminant calves revealed a biphasic SAA plasma disposition with a mean elimination half-life of 4.1 h. The main metabolite in plasma was N4-acetylsulphanilamide (N4), which 4 hours after injection exceeded the parent SAA plasma concentration. Urinary recovery of SAA was 10 to 16% of the dose; of N4, it was at least 69%. Traces of the N1-acetyl (N1) metabolite and the doubly acetylated derivative (N1N4) were present in urine. The renal clearances of the N1 and N4 metabolites showed a tubular secretion pattern, which was at least 2 to 6 times higher than that of SAA. A single high oral SAA dose of 200 mg/kg to 3 dairy cows resulted in extensive metabolism of SAA into N4, N1, and N1N4 metabolites; their mean maximum plasma concentrations were 64, 48, 0.72 and 24 micrograms/ml, respectively. The mean disposition half-life of SAA in plasma and milk was 10 h. In milk the metabolite concentrations exceeded those in plasma; the N4 and N1N4 metabolite concentrations in milk exceeded that of SAA. The mean maximum concentrations of SAA, N4, N1, and N1N4 in milk were 52, 89, 2.3, and 98 micrograms/ml, respectively. For SAA and its metabolites, the binding to plasma and milk proteins was determined. No glucuronide or sulphate conjugates of SAA and its acetyl metabolites could be found in plasma, milk, or urine. Based on the sensitivity of the bioassay (0.2 micrograms SAA/ml), a withholding time of 5 days was suggested for milk following single oral SAA dosage of 200 mg/kg.

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

Plasma disposition, protein binding, urinary recovery, and renal clearance of sulfamethazine (SMZ), sulfamerazine (SMR), and sulfadiazine (SDZ) and their N4-acetyl and hydroxy derivatives were studied in 4 horses in a crossover trial. The plasma concentration-time curves of the metabolites paralleled those of the parent drug in the elimination phase. Sulfamethazine and SMR were extensively metabolized. In plasma and urine, the main metabolite of the 3 sulfonamides tested was the 5-hydroxypyrimidine derivative, which was highly glucuronidated. Difference in elimination half-life of SMZ, SMR, and SDZ could be related to difference in metabolism and renal clearance values. Metabolism speeds drug elimination, producing compounds with higher renal clearance values than those of the parent drug. Methyl substitution in the pyrimidine side chain increased hydroxylation of the parent drug, but prolonged the persistence of the sulfonamides studied in the body. The high concentration of N4-acetyl and hydroxy metabolites of SMZ and SMR in plasma and urine decreased the potential antibacterial activity of the parent drugs. Sulfadiazine was less metabolized, and microbiologically determined SDZ concentrations in plasma and urine were slightly lower than those measured by high-performance liquid chromatography.

Residues of sulphadimidine and its metabolites in eggs following oral sulphadimidine medication of hens

The depletion of sulphadimidine (SDM) and its N4-acetyl and hydroxy metabolites was studied in eggs laid by hens after administration of either a single or multiple oral dosages of 100 mg SDM/kg. During medication and until 1 day after the last dose, the SDM and its metabolite concentrations in the egg white exceeded those in the egg yolk and reflected the plasma levels. In the period starting 2 days after the (last) dosage, the SDM concentration in the yolk became higher than in the egg white, and the drug depletion curves ran parallel. The mean maximum amount of SDM found in the whole egg was 1500 micrograms after a single and 1280 micrograms after multiple dosage. In eggs, traces of the N4-acetyl and 6-methylhydroxy metabolites could be detected (mainly in the egg white), and their concentrations were approximately 40 times lower than those of the parent drug. A highly significant correlation (P less than 0.005) was found between the development stage of the oocyte at the time of (last) medication and the amount of SDM found in the egg that developed from it. A period of 7 or 8 days after the (last) dosage of 100 mg SDM/kg/day is required to obtain SDM levels below 0.1 micrograms/g egg.

Acetylation and hydroxylation of sulphatroxazole in the snail Cepaea hortensis and the slug Arion rufus

The snail Cepaea hortensis can acetylate and hydroxylate sulphatroxazole via a pathway similar to that in man. The principal metabolic pathways, in order of decreasing rate, are hydroxylation, glucuronidation and acetylation. The slug Arion rufus also can acetylate and hydroxylate sulphatroxazole, although, in contrast to the snail, is rate of acetylation is higher than that of hydroxylation.

Pharmacokinetics, metabolism, and renal excretion of sulfadimidine and its N4-acetyl and hydroxy metabolites in humans

Sulfadimidine is acetylated and hydroxylated in humans. The hydroxylation pathways account for 10-20% of the dose, leaving the acetylation as the major metabolic pathway. The hydroxylation pathways are independent of the acetylator phenotype. The plasma concentration-time curve of sulfadimidine in fast acetylators is biphasic, with half-lives of 1.7 and 5.4 h, whereas that in slow acetylators is monophasic, with a half-life of 7.6 h. Hydroxylation of a methyl group in sulfadimidine lowers the protein binding from 90 to 60%, while acetylation does not affect the protein binding. Methyl hydroxylation markedly increases the renal clearance.

Effect of the injection site on the pharmacokinetics of procaine penicillin G in horses

The plasma penicillin concentrations were determined in 5 horses given an IV injection of sodium penicillin G; plasma penicillin concentrations were also determined in a crossover experiment, where animals were given procaine penicillin G subcutaneously at 1 site and IM at 4 sites. The mean penicillin plasma peak concentration and bioavailability were highest after the drug was injected in the neck and biceps musculature. Injections in the gluteal muscle and in the subcutaneous sites resulted in similar, but lower, more persistent penicillin plasma concentrations and a lower bioavailability than were obtained with injection in the neck and biceps musculature. The pharmacokinetic data obtained after penicillin was administered via the pectoral muscle route exhibited an intermediate position. Therapeutic implications of the routes of administration with respect to hemolytic streptococcal infections are discussed.

Chemotherapy and pharmacokinetics of some antimicrobial agents in healthy dwarf goats and those infected with Ehrlichia phagocytophila (tick-borne fever)

The therapeutic efficacy and pharmacokinetics of oxytetracycline (10 mg kg-1), ampicillin (20 mg kg-1) and a combination (TSS) of trimethoprim (20 mg kg-1), sulphadimidine (50 mg kg-1) and sulphamethylphenazole (50 mg kg-1) were investigated in normal dwarf goats and in those infected with Ehrlichia phagocytophila. Goats given oxytetracycline or TSS intravenously showed improvement, whereas ampicillin was ineffective. The infected goats had significantly prolonged elimination half-life values for sulphadimidine and oxytetracycline. The disposition kinetics of ampicillin and sulphamethylphenazole showed no marked differences between the healthy and infected animals. The tick-borne fever model used in the present study can be of value in testing the therapeutic efficacy and pharmacokinetics of chemotherapeutic agents in rickettsial infections.

Age difference in pharmacokinetics of an amoxycillin trihydrate-15% formulation administered intramuscularly to ruminants

Intramuscular administration of an amoxycillin trihydrate-15% formulation to three groups of animals revealed in preruminant calves (age 3-4 weeks) significant higher plasma peak drug concentrations and shorter biological half-lives than in 5-month-old ruminant calves and dairy cows. Differences in pharmacokinetics were related to age-difference in drug absorption capability at the injection site regarding the formulation.

Pharmacokinetics and renal clearance of oxytetracycline in piglets following intravenous and oral administration

The pharmacokinetics of oxytetracycline (OTC) in three weaned piglets was studied following three routes of administration: intravenously, orally as drench, both at a dose of 20 mg/kg, and orally as medicated (400 ppm OTC) pelleted feed administered during 3 consecutive days. Analysis of the intravenous data according to the three compartment pharmacokinetic model revealed that OTC was well distributed in the body (Vf: 1.62 l/kg), had an overall body clearance of 0.25 litre/kg/h, and the elimination half-lives were in the range between 11.6 and 17.2 hrs. The mean OTC binding to plasma proteins was 75.5 +/- 4%. Following the drench route of administration the maximum plasma OTC concentration was achieved between 1 and 5 h post application and ranged between 1.18 and 1.41 micrograms/ml. The mean maximum plasma OTC concentration during medicated feed administration was 0.20 +/- 0.06 microgram/ml, which was achieved approximately 30 hours after the onset of the administration. A steady state OTC plasma level (approximately 0.2 microgram/ml) was maintained till the end of the trial. Within 48 hours after cessation of medicated feed administration the plasma OTC levels were beneath 0.06 microgram/ml. The mean OTC bioavailabilities of the oral routes were low: after the drench route of administration 9.0 +/- 0.67%, and after medicated pelleted feed administration 3.69 +/- 0.8%. The mean OTC renal clearances of each piglet ranged between 10.1 and 13.9 ml/min/kg (based on free OTC plasma fractions). The renal OTC clearance values were urine flow dependent in all piglets and significantly correlated with the renal creatinine clearance (P less than 0.005), being 3-5 times higher than the latter. It is concluded that in piglets OTC is excreted mainly by glomerular filtration and partly by tubular secretion. The potential clinical efficacy of 400 ppm OTC as medicated feed with respect to treatment, e.g. atrophic rhinitis, is discussed.

Comparative pharmacokinetics, bioavailability and renal clearance of five parenteral oxytetracycline-20% formulations in dairy cows

Oxytetracycline (OTC) concentrations on plasma and milk of dairy cows were determined following a single intramuscular injection of five oxytetracycline-20% formulations at a dosage of approximately 10 mg/kg. For obtaining pharmacokinetic reference parameters, one 10% OTC formulation was administered intravenously. The five 20% formulations were compared and evaluated pharmacokinetically with respect to absorption rate, peak plasma and milk OTC concentrations, biological half-life, and relative bioavailability. The mean maximum plasma OTC concentrations varied between 4.5 and 6.8 micrograms/ml and were achieved between 5 and 10 h p.i., depending on the formulation involved. The mean maximum milk concentrations, ranging from 1.12 to 1.92 micrograms/ml, were achieved 12 to 24 h p.i. A plasma OTC concentration exceeding 0.5 microgram/ml was maintained for 48 h to 70 h, and in milk for 33 to 49 h, depending on the formulation involved. Formulations exhibiting the lowest clinically noticeable irritation showed the highest peak plasma OTC concentrations and the best bioavailability. Among the formulations the calculated withholding periods for milk were in the range of 3 to 4 days and for edible tissues of 9 to 14 days. The OTC and creatinine clearances were significantly correlated to each other and to the urinary flow. OTC was excreted predominantly by glomerular filtration, partly by tubular secretion minus urogenital (distal renal tubuli and bladder) reabsorption.

Pharmacokinetic, residue and irritation aspects of chloramphenicol sodium succinate and a chloramphenicol base formulation following intramuscular administration to ruminants

The disposition of chloramphenicol (CAP) and of its glucuronide metabolite in plasma and milk was studied following a single intramuscular injection of a chloramphenicol base formulation (Amicol Forte; product A) and of chloramphenicol sodium succinate (product B) to dairy cows. The dose applied of both formulations was equivalent to 50 mg CAP base/kg body weight. The HPLC determined CAP concentrations were microbiologically active. Product A revealed 30% higher plasma CAP peak concentrations (13.0 vs 9.0 micrograms/ml) and 36% larger areas under the plasma concentration-time curves than product B, whereas their absorption and elimination half-lives were of the same order of magnitude. In the onset phase (during 4 h p.i.) unhydrolysed CAP sodium succinate could be detected in plasma and the glucuronide fraction was 26% of the parent drug. After 25 h p.i. the glucuronide fraction equalled that of the parent drug. The maximum CAP concentration in milk was for product B equal to, and for product A 80% of, the CAP plasma concentration. In milk no chloramphenicol glucuronide metabolites could be detected. HPLC methods for detecting ultra-trace CAP concentrations in edible tissues were developed by the employment of extraction with or without a clean-up procedure. Seven days after i.m. administration of product A and B to calves, the CAP residue concentrations in the kidney, liver, and muscle were less than 2 nanogram/g tissue. Traces of CAP residues could be still found at the injection site and in the urine. Chloramphenicol sodium succinate (product B) caused extensive tissue irritation at the injection site, while in the case of product A the irritation was limited.(ABSTRACT TRUNCATED AT 250 WORDS)

Fish and antibiotics: pharmacokinetics of sulphadimidine in carp (Cyprinus carpio)

Pharmacokinetics, metabolism and clearance of sulphadimidine (SDM) were studied after a single intraperitoneal injection of SDM in carp at 20 degrees C. SDM was acetylated and hydroxylated to a small extent. The main metabolite was N4-acetyl derivative amounting only 2% of the total drug dose excreted; hydroxylation was less important (0.41% of the dose). The elimination half-life for SDM in carp was 17.5 h. The clearance values for SDM and its metabolites were equivalent. The importance of pharmacokinetic studies in different fish species is discussed.

Pharmacokinetics, metabolism and renal excretion of sulfatroxazole and its 5-hydroxy- and N4-acetyl-metabolites in man

Hydroxylation is the predominant pathway of metabolism for sulfatroxazole in the body, accounting for 70 per cent of the dose. Fifteen per cent of the dose is acetylated unimodally and 10 per cent is excreted unchanged. The half-lives of sulfatroxazole and its metabolites 5-hydroxysulfatroxazole and N4-acetylsulfatroxazole are approximately 22 h after administration of sulfatroxazole. N4-acetylsulfatroxazole, taken as parent drug, is eliminated by renal excretion (92 per cent of the dose). The initial elimination half-life of N4-acetylsulfatroxazole is 4.5 h, which later increases to 70 h as the result of the acetylation-deacetylation equilibrium. Probenecid inhibits the renal excretion of the metabolites 5-hydroxy- and N4-acetylsulfatroxazole. Inhibition of the N4-acetyl metabolite favours the deacetylation, which results in an increase of the T 1/2 of sulfatroxazole from 20 to 30 h. The protein binding value of sulfatroxazole is 84 per cent, that of N4-acetylsulfatroxazole is 37 per cent. Sulfatroxazole is excreted renally by passive processes, while the metabolites are excreted by both passive and active processes.