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

The plasma and tissue kinetics of sulfadiazine and its metabolite in Ictalurus punctatus after oral gavage at two temperatures

A plasma and tissue kinetic study of sulfadiazine (SDZ) and its metabolite, N₄ -acetyl sulfadiazine (ACT-SDZ), was characterized in channel catfish (Ictalurus punctatus) following a single oral dose of 50 mg/kg at 18 and 24°C. Samples were collected at predetermined time points and determined by ultra-performance liquid chromatography. The classical one-compartmental method was used to estimate the pharmacokinetic parameters. Results showed that the changing of temperature was markedly influential on the kinetics of SDZ and ACT-SDZ in plasma and tissues. When the temperature was increased from 18 to 24°C, the elimination half-life (K10_HF) of SDZ was decreased in gill, kidney, and muscle + skin, but increased in liver and plasma. The K10_HF of ACT-SDZ also had a decreased trend in gill, liver, and plasma but had comparable values in kidney and muscle + skin. The absorption half-life (K01_HF), time to peak concentration (T_max ), and area under concentration-time curve (AUC_0-∞ ) of SDZ and ACT-SDZ all exhibited declined tendencies in plasma and tissues. The apparent volume of distribution (V_F) of SDZ in plasma was increased from 0.53 to 1.48 L/kg, and the apparent systemic total body clearance (Cl_F) was increased from 0.028 to 0.060 L/h/kg. In a word, K01_HF, T_max , and AUC_0-∞ of SDZ and ACT-SDZ were decreased in plasma and tissues with the increase of temperature, whereas the V_F and Cl_F of SDZ were increased. Meanwhile, we calculated the percentage of time profile of SDZ concentration more than minimum inhibitory concentration to total time (%T > MIC) to guide clinical usage of SDZ. When the dosage interval was 24 h, the values of %T > MIC were all >90% in plasma and most tissues. Therefore, we recommend an oral dose of SDZ at 50 mg/kg once per 24 h at 18-24°C against the fish pathogens with an MIC value of ≤6.4 μg/mL.

Metabolic Disposition and Elimination of Tritum-Labeled Sulfamethoxazole in Pigs, Chickens and Rats

Sulfamethoxazole (SMZ), as a sulfa antibiotic, is often used in the treatment of various infectious diseases in animal husbandry. At present, SMZ still has many unresolved problems in the material balance, metabolic pathways, and residual target tissues in food animals. Therefore, in order to solve these problems, the metabolism, distribution, and elimination of SMZ is investigated in pigs, chickens, and rats by radioactive tracing methods, and the residue marker and target tissue of SMZ in food animals were determined, providing a reliable basis for food safety. After a single administration of [³H]-SMZ (rats and pigs by intramuscular injection and chickens by oral gavage), the total radioactivity was rapidly excreted, with more than 93% of the dose excreted within 14 days in the three species. Pigs and rats had more than 75% of the administered volume recovered by urine. After 7 days of continuous administration, within the first 6 h, radioactivity was found in almost all tissues. The highest radioactivity and longest persistence in pigs was in the liver, while in chickens it was in the liver and kidneys, most of which was removed within 14 days. A total of six, three and three metabolites were found in chickens, rats and pigs, respectively. N₄-acetyl-sulfamethoxazole (S1) was the main metabolite of SMZ in rats, pigs and chickens. The radioactive substance with the longest elimination half-life is sulfamethoxazole (S0), so S0 was suggested to be the marker residue in pigs and chickens.

Comparative Pharmacokinetics of Sulfadiazine and Its Metabolite N4-Acetyl Sulfadiazine in Grass Carp (Ctenopharyngodon idella) at Different Temperatures after Oral Administration

In this study, the plasma pharmacokinetics and tissue disposition of sulfadiazine (SDZ) and its main metabolite, N₄-acetyl sulfadiazine (ACT-SDZ), were compared between 18 and 24 °C following a single oral administration of SDZ at 50 mg/kg in grass carp (Ctenopharyngodon idella). The plasma and tissues were sampled from 0.167 h up to 96 h and analyzed by ultra-performance liquid chromatography with an ultraviolet detector. The pharmacokinetic parameters were estimated using a one-compartmental approach. Results showed that pharmacokinetics of SDZ and ACT-SDZ in plasma and tissues were notably influenced by the increase of temperature. The increased temperature shortened the absorption half-life (K01_HL) of SDZ and ACT-SDZ in gill, kidney, and plasma, but increased in liver and muscle + skin. The elimination half-life (K10_HF) and the area under concentration-time curve (AUC_0–∞) of SDZ and ACT-SDZ all presented a declined trend. The apparent volume of distribution (V_F) of SDZ in plasma was increased from 0.93 to 1.64 L/kg, and the apparent systemic total body clearance (Cl_F) was also increased from 0.01 to 0.05 L/h/kg. Overall, the rise of temperature decreased K10_HF, AUC_0–∞ of SDZ, and ACT-SDZ in plasma and tissues, but increased V_F and Cl_F in the plasma for SDZ.

Veterinary antibiotics in swine and cattle wastewaters of China and the United States: Features and differences

Veterinary antibiotics (VAs) have been widely used in livestock for disease prevention, treatment, and growth promotion. This study compared top 20 VAs in Chinese and US swine and cattle wastewater with published literatures. The sulfonamides (SAs) were found to be predominant, accounting for 62% of the top 20 VAs in Chinese swine wastewater, while tetracyclines (TCs) contributed to about 68.7% of the 18 VAs in US swine wastewater. The average concentration of the 20 major VAs in Chinese swine wastewater was estimated to be 1145 μg/L against 253.6 μg/L in the United States. On the other hand, the five major VAs in Chinese cattle wastewater were identified to be oxytetracycline, nafcillin, apramycin, lincomycin, and amikacin, while monensin was found to be dominant in US cattle wastewater. The average concentration of the top 20 VAs in Chinese and US cattle wastewaters were found to be 54.6 and 46.2 μg/L, respectively. These analyses suggested that VAs were probably over-used in Chinese swine industry, eventually causing the development and spreading of antibiotic resistant-bacteria and genes, which should be paid with attention. PRACTITIONER POINTS: Major veterinary antibiotics (VAs) in swine and cattle wastewater were identified. Top 20 VAs in swine and cattle wastewater of China and the United States were compared. VAs concentration in Chinese swine wastewater was 4.52 times that in the United States. VAs concentration in Chinese cattle wastewater was 1.18 times that of the United States.

Bioaccumulation, Biotransformation, and Multicompartmental Toxicokinetic Model of Antibiotics in Sea Cucumber (Apostichopus japonicus)

Extensive application of antibiotics leads to their ubiquitous occurrence in coastal aquatic environments. However, it remains largely unknown whether antibiotics can be bioaccumulated and biotransformed in major mariculture organisms such as sea cucumbers and toxicokinetic models for Echinodermata are lacking. In this study, laboratory exposure experiments on juvenile sea cucumber (Apostichopus japonicus) were performed for seven antibiotics (sulfadiazine, sulfamethoxazole, trimethoprim, enrofloxacin, ofloxacin, clarithromycin, and azithromycin). Field sea cucumber and surrounding seawater samples were also analyzed. Results show that the sea cucumbers tend to accumulate high concentrations of the antibiotics with kinetic bioconcentration factors (BCFs) up to 1719.7 L·kg^-1 for ofloxacin. The BCFs determined in the laboratory agree well with those estimated from the field measurements. Seven biotransformation products (BTPs) of the antibiotics were identified, four of which were not reported previously in aquatic organisms. The BTPs were mainly found in the digestive tract, indicating its high capacity in the biotransformation. A multicompartmental toxicokinetic model based on the principles of passive diffusion was developed, which can successfully predict time-course concentrations of the antibiotics in different compartments of the juvenile sea cucumbers. The findings may offer a scientific basis for assessing health risks and guiding healthy mariculture of sea cucumbers.

Biocompatibility and antibacterial activity of photolytic products of sulfonamides

BACKGROUND

This study assessed the photochemical fate of nine sulfonamides (sulfamerazine, sulfanilamide, sulfamethoxypyridazine, sulfamethoxazole, sulfachloropyridazine, sulfamethazine, sulfadiazine, sulfathiazole and sulfadimethoxine) during a 6h irradiation period with UVA/UVB-light and UVA-light and over 7 days under natural (sunlight) conditions. The cell growth inhibition effect and cytotoxicity of sulfonamides and their photodegradation products was investigated over 24 and 48 h with murine fibroblasts and keratinocytes. Antibacterial activity of the degradation products was studied using the Geobacillus stearothermophilus var. Calidolactis C953 assay.

RESULTS

UVA/UVB treatment of several sulfonamide solutions results in degradation of the compounds in different amounts with the highest degradation rate for sulfathiazole and sulfanilamide. The UVA/UVB light degradation products exhibit no antimicrobial activity. Sun light exposure over 7 days reveals a similar degradation pattern of the different sulfonamides, albeit to a different extent. Compared with UVA/UVB-irradiation, UVA-irradiated sulfonamides degrade to a lesser extent (except sulfamethazine). There was no impact on cell toxicity of the UVA/UVB-degrading products except for sulfanilamide, while a slight impact on cell proliferation was observed.

CONCLUSIONS

All studied sulfonamides undergo photodegradation under UV-light exposure to a greater or lesser extent. The degradation products have no cytotoxic potential except sulfanilamide and have a slight impact on cell proliferation. All degradation products showed no antibacterial activity. Thus, UV-light exposure seems to represent an adequate method for inactivating sulfonamides with regard to their antimicrobial activity.

Transport and transformation of sulfadiazine in soil columns packed with a silty loam and a loamy sand

Concerning the transport of the veterinary antibiotic sulfadiazine (SDZ) little is known about its possible degradation during transport. Also its sorption behaviour is not yet completely understood. We investigated the transport of SDZ in soil columns with a special emphasis on the detection of transformation products in the outflow of the soil columns and on modelling of the concentration distribution in the soil columns afterwards. We used disturbed soil columns near saturation, packed with a loamy sand and a silty loam. SDZ was applied as a 0.57 mg L(-1) solution at a constant flow rate of 0.25 cm h(-1) for 68 h. Breakthrough curves (BTC) of SDZ and its transformation products 4-(2-iminopyrimidin-1(2H)-yl)aniline and 4-hydroxy-SDZ were measured for both soils. For the silty loam we additionally measured a BTC for an unknown transformation product which we only detected in the outflow samples of this soil. After the leaching experiments the (14)C-concentration was quantified in different layers of the soil columns. The transformation rates were low with mean SDZ mass fractions in the outflow samples of 95% for the loamy sand compared to 97% for the silty loam. The formation of 4-(2-iminopyrimidin-1(2H)-yl)aniline appears to be light dependent and did probably not occur in the soils, but afterwards. In the soil columns most of the (14)C was found near the soil surface. The BTCs in both soils were described well by a model with one reversible (kinetic) and one irreversible sorption site. Sorption kinetics played a more prominent role than sorption capacity. The prediction of the (14)C -concentration profiles was improved by applying two empirical models other than first order to predict irreversible sorption, but also these models were not able to describe the (14)C concentration profiles correctly. Irreversible sorption of sulfadiazine still is not well understood.

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.

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.

Metabolism of 14C-labelled and non-labelled sulfadiazine after administration to pigs

The behaviour of sulfadiazine (SDZ) and its metabolites was investigated by administering the (14)C-labelled veterinary drug to fattening pigs. The excretion kinetics were determined after daily collection of manure. Two known metabolites, N-acetylsulfadiazine and 4-hydroxysulfadiazine, and two hitherto unidentified minor metabolites were recovered. Various mass spectrometric techniques such as parent, product ion scans and accurate mass measurement were used. The new compounds were identified as N-formylsulfadiazine (For-SDZ) and N-acetyl-4-hydroxysulfadiazine (Ac-4-OH-SDZ). The identification of SDZ, Ac-SDZ and For-SDZ was confirmed by comparison of the spectroscopic and chromatographic data of the synthesized authentic references. The identification of the hydroxylated compounds 4-OH-SDZ and Ac-4-OH-SDZ was performed by MSn, and accurate mass measurements. Only 4% of the administered radioactivity remained in the pig after ten days and SDZ accounted for 44% of the 96% radioactivity excreted. More than 93% of the labelled compounds were detected and identified in the manure. The key analytical problem, namely a high concentration of matrix in sample extracts, was overcome by advanced measurement techniques and with the use of a suitable internal standard. The mean recoveries for all compounds were >or=96%. Linearity was established over a concentration range of 0.5 to 10,000 microg kg(-1) manure with a correlation coefficient>or=0.99. The same experiment was carried out simultaneously with non-labelled SDZ to obtain manure for outdoor soil experiments.

Use of probabilistic modeling within a physiologically based pharmacokinetic model to predict sulfamethazine residue withdrawal times in edible tissues in swine

The presence of antimicrobial agents in edible tissues of food-producing animals remains a major public health concern. Probabilistic modeling techniques incorporated into a physiologically based pharmacokinetic (PBPK) model were used to predict the amounts of sulfamethazine residues in edible tissues in swine. A PBPK model for sulfamethazine in swine was adapted to include an oral dosing route. The distributions for sensitive parameters were determined and were used in a Monte Carlo analysis to predict tissue residue times. Validation of the distributions was done by comparison of the results of a Monte Carlo analysis to those obtained with an external data set from the literature and an in vivo pilot study. The model was used to predict the upper limit of the 95% confidence interval of the 99th percentile of the population, as recommended by the U.S. Food and Drug Administration (FDA). The external data set was used to calculate the withdrawal time by using the tolerance limit algorithm designed by FDA. The withdrawal times obtained by both methods were compared to the labeled withdrawal time for the same dose. The Monte Carlo method predicted a withdrawal time of 21 days, based on the amounts of residues in the kidneys. The tolerance limit method applied to the time-limited data set predicted a withdrawal time of 12 days. The existing FDA label withdrawal time is 15 days. PBPK models can incorporate probabilistic modeling techniques that make them useful for prediction of tissue residue times. These models can be used to calculate the parameters required by FDA and explore those conditions where the established withdrawal time may not be sufficient.

Structural characterization of sulfadiazine metabolites using H/D exchange combined with various MS/MS experiments

Two major metabolites and one minor metabolite of sulfadiazine were found in pig manure, using a special combination of different MS techniques like parent and product ion scans, H/D exchange, accurate mass measurement, and MS/MS experiments with substructures. N4-acetylsulfadiazine and 4-hydroxysulfadiazine were identified as major metabolites. N4-acetylsulfadiazine could be verified by H/D exchange and comparison with product ion spectra of a synthetic reference compound. In the case of 4-hydroxysulfadiazine, the majority of possible isomers could be discounted after H/D exchange. Substructure-specific MS/MS experiments with fragment ions and comparison with product ion spectra of two references revealed the presence of 4-hydroxysulfadiazine. The minor metabolite was characterized to some degree using H/D exchange and tandem mass spectrometry in combination with a high-resolution time of flight mass spectrometer. The aminopyrimidine moiety contained an additional modification with a likely elemental composition of C2H4O and no further acidic hydrogen.

Development of a physiologic-based pharmacokinetic model for estimating sulfamethazine concentrations in swine and application to prediction of violative residues in edible tissues

OBJECTIVE

To develop a flow-limited, physiologic-based pharmacokinetic model for use in estimating concentrations of sulfamethazine after IV administration to swine.

SAMPLE POPULATION

4 published studies provided physiologic values for organ weights, blood flows, clearance, and tissue-to-blood partition coefficients, and 3 published studies provided data on plasma and other tissue compartments for model validation.

PROCEDURE

For the parent compound, the model included compartments for blood, adipose, muscle, liver, and kidney tissue with an extra compartment representing the remaining carcass. Compartments for the N-acetyl metabolite included the liver and the remaining body. The model was created and optimized by use of computer software. Sensitivity analysis was completed to evaluate the importance of each constant on the whole model. The model was validated and used to estimate a withhold interval after an IV injection at a dose of 50 mg/kg. The withhold interval was compared to the interval estimated by the Food Animal Residue Avoidance Databank (FARAD).

RESULTS

Specific tissue correlations for plasma, adipose, muscle, kidney, and liver tissue compartments were 0.93, 0.86, 0.99, 0.94, and 0.98, respectively. The model typically overpredicted concentrations at early time points but had excellent accuracy at later time points. The withhold interval estimated by use of the model was 120 hours, compared with 100 hours estimated by FARAD.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of this model enabled accurate prediction of sulfamethazine pharmacokinetics in swine and has applications for food safety and prediction of drug residues in edible tissues.

Pharmacokinetics of sulfadimethoxine and sulfamethoxazole in combination with trimethoprim after oral single- and multiple-dose administration to healthy pigs

The pharmacokinetics were studied of sulfadimethoxine (SDM) or sulfamethoxazole (SMX) in combination with trimethoprim (TMP) administered as a single oral dose (25 mg + 5 mg per kg body weight) to two groups of 6 healthy pigs. The elimination half-lives of SMX and TMP were quite similar (2-3 h); SDM had a relatively long half-life of 13 h. Both sulfonamides (S) were exclusively metabolized to N4-acetyl derivatives but to different extents. The main metabolic pathway for TMP was O-demethylation and subsequent conjugation. In addition, the plasma concentrations of these drugs and their main metabolites after medication with different in-feed concentrations were determined. The drug (S:TMP) concentrations in the feed were 250:50, 500:100, and 1000:200 mg per kg. Steady-state concentrations were achieved within 48 h of feed medication, twice daily (SDM+TMP) or three times a day (SMX+TMP). Protein binding of SDM and its metabolite was high (>93%), whereas SMX, TMP and their metabolites showed moderate binding (48-75%). Feed medication with 500 ppm sulfonamide combined with 100 ppm TMP provided minimum steady-state plasma concentrations (C(ss,min)) higher than the concentration required for inhibition of the growth of 90% of Actinobacillus pleuropneumoniae strains (n = 20).

Deacetylation as a determinant of sulphonamide pharmacokinetics in pigs

Sulphamonomethoxine (SMM), sulphadimidine (SDD), sulphadiazine (SDZ) and their N4-acetyl derivatives (AcSMM, AcSDD and AcSDZ) were intravenously injected into Goettingen miniature pigs and deacetylation was evaluated from plasma concentration-time curves, renal excretion, and rate constants obtained from pharmacokinetic analysis, using a non-linear least-squares method. Deacetylated metabolite was detected in both plasma and urine after intravenous injection of AcSMM, AcSDD and AcSDZ. The area under the curve (AUC) values for the deacetylated metabolite were significantly higher than those for acetyl derivatives after AcSMM and AcSDD administration, but significantly lower after AcSDZ. After AcSMM and AcSDD injection, the concentration ratio between deacetylated metabolite and acetyl derivative was almost constant in the terminal linear phase and similar to that seen after injection of sulphonamide. After AcSDZ injection, however, a constant ratio was not observed. These results indicate that deacetylation can have a significant effect on the pharmacokinetics of SMM and SDD, but not on those of SDZ in pigs. The rate constant for deacetylation was significantly higher than that for acetylation for SMM and SDD, but significantly lower for SDZ. It is, therefore, concluded that deacetylation may be a determinant of the pharmacokinetics of SMM and SDD in pigs. It was, however, not a determinant of SDZ pharmacokinetics because N4-acetylation is not the main elimination route in pigs.

A study of the pharmacokinetics and tissue residues of an oral trimethoprim/sulphadiazine formulation in healthy pigs

Twenty-six healthy female pigs weighing 19.5-33 kg were used in three separate experiments. The animals were fed individually twice a day. Trimethoprim/sulphadiazine (TMP/SDZ) formulation was added to feed in the amount of 6 mg/kg bw (TMP) and 30 mg/kg bw (SDZ). TMP and SDZ concentrations in blood plasma, muscles, liver and kidneys were measured. Pharmacokinetic parameters show that the absorption of TMP from the alimentary tract in pigs is faster than the absorption of SDZ, and the elimination of TMP is slower than that of SDZ. The absorption half-lives were 0.96 (TMP) and 2.24 h (SDZ), whereas elimination half-lives were 5.49 (TMP) and 4.19 h (SDZ). The observed TMP:SDZ ratios in blood plasma after multiple dose administration ranged from 1:11.4 to 1:23.2. One day after administration of the last dose of TMP/SDZ the plasma concentration ratio was 1:15.5, but in muscles, liver and kidneys it was much lower: 1:0.79, 1:0.14 and 1:1.53 respectively. The absolute TMP and SDZ tissue concentrations 1 day after the last multiple dose administration were very low (maximum TMP: 0.29 micrograms/g in liver; maximum SDZ: 0.23 micrograms/g in kidneys). Neither drug was detected in any tissue 8 days after the last administration of TMP/SDZ. Based on our results, it was concluded that there is no support for the TMP:SDZ pharmaceutical ratio 1:5 in oral formulations of these compounds for pigs. The administration oral TMP/SDZ formulations once a day may result in the absolute tissue concentrations of these drugs being too low for antibacterial activity. The withdrawal period for such an oral TMP/SDZ formulation for pigs (according to accepted guidelines in Europe for MRL of TMP < 0.05 mg/kg of tissue) should not be less than 5 days.

Absorption, tissue distribution, metabolism and excretion of ormetoprim and sulphadimethoxine in Atlantic salmon (Salmo salar) after intravenous and oral administration of Romet

1. Uptake, bioavailability, tissue disposition and elimination of sulphadimethoxine (SDM) and ormetoprim (OMP) were examined in Atlantic salmon (Salmo salar) following intravenous and oral administration of Romet at a dose of 5 mg OMP and 25 mg SDM kg-1 fish. 2. Plasma clearance was rapid for both drugs following a single i.v. dose, characterized by t1/2 alpha = 0.48 and 0.54h, t1/2 beta = 9.9 and 25.6h for SDM and OMP respectively with a volume of distribution (Vss) = 0.389 and 2.478 l kg-1. 3. Following oral administration, peak plasma concentrations of 1.13 and 9.99 micrograms ml-1 were achieved after 17.6 and 20.3h for OMP and SDM respectively. Bioavailabilities were 85% for OMP and 39% for SDM. 4. Oral administration revealed the highest concentration of OMP in kidney and liver whereas the highest concentrations of SDM were found in muscle and bile. 5. High concentrations of N4-acetylated SDM were found in the bile indicating significant metabolism of SDM.

Oral bioavailability of sulphonamides in ruminants: a comparison between sulphamethoxazole, sulphatroxazole, and sulphamerazine, using the dwarf goat as animal model

The various sulphonamides show marked differences in disposition characteristics after administration to ruminants. For use in combination with a diaminopyrimidine derivative such as trimethoprim or baquiloprim, it is essential that a sulphonamide has similar pharmacokinetic properties in order to obtain optimal synergy. In the present study the pharmacokinetics of sulphamethoxazole, sulphatroxazole, and sulphamerazine were investigated in dwarf goats (n = 6) after IV and intraruminal administration at a dose of 30 mg/kg bodyweight. In addition, the in vitro binding of sulphamerazine to ruminal contents was studied as a possible explanation for a reduced absorption rate. Sulphamethoxazole showed the most rapid absorption after intraruminal administration (mean tmax +/- SD : 0.8 +/- 0.2h). However, the drug was rapidly eliminated from the plasma (t1/2 beta : 2.4 +/- 1.5 h) and the bioavailability was only 12.4 +/- 4.7%, most likely due to an extensive 'first-pass' effect. The bioavailability of orally administered sulphamerazine and sulphatroxazole was much higher (67.6 +/- 13.5% and 70.2 +/- 32.3%, respectively). After intraruminal administration, sulphatroxazole showed the highest plasma peak concentration (26.1 +/- 6.3 mg/l) and the longest plasma half-life (4.7 +/- 1.8h) and mean residence time (13.9 +/- 4.5 h). Sulphamerazine showed considerable binding to rumen contents in vitro. Based on its pharmacokinetic properties sulphatroxazole appears to be a suitable candidate to be used in combination with the more recently developed diaminopyrimidines such as baquiloprim.

Pharmacokinetics of sulfadimethoxine and sulfamethoxazole in combination with trimethoprim after intravenous administration to healthy and pneumonic pigs

The pharmacokinetics of two sulfonamide/trimethoprim combinations were investigated after intravenous administration to clinically healthy pigs and to the same pigs following a challenge with Actinobacillus pleuropneumoniae toxins. Endobronchial challenge with A. pleuropneumoniae toxins resulted in fever, increased white blood cell counts and decreased water and feed consumption. Healthy, as well as febrile, pigs were given sulfadimethoxine (SDM) or sulfamethoxazole (SMX) intravenously at a dose of 25 mg/kg b.w. in combination with 5 mg trimethoprim (TMP) per kg body weight. The pharmacokinetic parameters of the sulfonamides as well as their main metabolites (acetyl sulfonamides) were not significantly different in healthy and febrile pigs. In healthy and pneumonic pigs, the mean elimination half-lives of SDM were 12.9 h and 13.4 h, respectively, those of SMX 2.5 h and 2.7 h, respectively, and those of TMP 2.8 h and 2.6 h, respectively. Distribution volumes in healthy and febrile pigs of SDM and SMX varied between 0.2 and 0.4 L/kg, and those of TMP between 1.1 and 1.6 L/kg. The mean AUC of TMP was decreased and the volume of distribution and total body clearance of TMP were increased in febrile pigs. Protein binding of the drugs and metabolites studied were not significantly changed after toxin-induced fever. The extent of protein binding of SDM, SMX and TMP was in the range 94-99%, 45-56% and 40-50%, respectively. Based on knowledge of in vitro antimicrobial activity of the drug combinations against A. pleuropneumoniae it was concluded that after intravenous administration of the dose administered (30 mg/kg of the combination preparations) to healthy and pneumonic pigs, plasma concentrations of SMX and TMP were above the concentration required for growth inhibition of 50% of A., pleuropneumoniae strains for approximately 16 h, whereas bacteriostatic plasma concentrations of SDM were still present after TMP had been eliminated from plasma. Because of similar elimination half-lives of SMX and TMP in pigs this combination is preferred to the combination of SDM with TMP.

Pharmacokinetics of baquiloprim and sulphadimidine in pigs after intramuscular administration

Baquiloprim, a novel 5-substituted 2, 4-diaminopyrimidine, has been developed specifically for veterinary use. It has been formulated as an injectable preparation and combined with sulphadimidine to exploit the synergistic activity of the two antibacterial agents. The formulation was given by deep intramuscular injection to pigs at doses of 10 mg kg-1 and 30 mg kg-1 and the pharmacokinetic properties were investigated. The in vitro activity of the two components was also determined against a range of porcine pathogens. Both components were rapidly absorbed and the maximum concentrations of 0.55 microgram ml-1 baquiloprim and 15.6 micrograms ml-1 sulphadimidine observed after the administration of the lower dose were well in excess of the minimum inhibitory concentration (MIC) values against susceptible pathogens, the highest combined MIC90 being 0.06 microgram ml-1 baquiloprim + 6.25 micrograms ml-1 sulphadimidine. Concentrations above the MIC values of most pathogens were maintained for more than 24 and 48 hours after the administration of the lower and higher doses, respectively. The volumes of distribution of 2.41 litre kg-1 observed after the lower dose and 4.60 litre kg-1 after the higher dose indicated that baquiloprim was well distributed and concentrated in tissues. These findings suggest that the formulation should be effective in the treatment of bacterial infections in pigs.

Transdermal delivery and intramuscular injection of trimethoprim/sulphadiazine in sucking piglets

The pharmacokinetics of a combination of trimethoprim (TMP) and sulphadiazine (SDZ) after topical application to sucking piglets was compared with the pharmacokinetics after intramuscular injection. A long-lasting and fairly constant SDZ/TMP concentration ratio in plasma was obtained after topical application. The mean plasma concentration of TMP ranged from 0.091 to 0.17 micrograms/ml and that of SDZ from 0.72 to 1.1 micrograms/ml for at least 24 h. TMP and SDZ had different half-lives after intramuscular injection. Transdermal delivery of a combined preparation of TMP/SDZ may be usable for colibacillosis of sucking piglets, although the bioavailability of the drugs is poor.

Pharmacokinetics and acetylation of sulfa-2-monomethoxine in humans

In humans sulfa-2-monomethoxine (S) is metabolized by N4-acetylation (39.9 +/- 8.0 per cent). After an oral dose, S is eliminated biphasically (t1/2, 5.2 +/- 1.6 h and 13.2 +/- 3.4 h) which is similar in both fast and slow acetylators. The metabolite N4-acetylsulfa-2-monomethoxine (N4) is eliminated monophasically (t1/2, 30.0 +/- 5.7 h). The intrinsic mean residence time (MRT) of N4 is 33.5 +/- 8.8 h. The mean total body clearance of S is 11.6 +/- 2.7 ml min-1, and the Vdss is 12.3 +/- 1.01. The renal clearance of S during the first day was twice as high as on the following days for two of the six volunteers (8 vs 4 ml min-1). The renal clearance of N4 during the first day, for four out of the six volunteers, was twice as high as on the following days (8 vs 4 ml min-1). The protein binding of S is 95 per cent and that of its conjugate N4 98 per cent. Approximately 80 per cent of the oral dose of S is excreted in the urine as parent drug (41.0 +/- 6.2 per cent) and as N4 acetyl conjugate (39.9 +/- 8.0 per cent).

Pharmacokinetics, N1-glucuronidation and N4-acetylation of sulfamethomidine in humans

Sulfamethomidine metabolism was studied in 6 volunteers. In humans, only N1-glucuronidation and N4-acetylation take place, leading to the final double conjugate N4-acetylsulfamethomidine N1-glucuronide. The N1-glucuronides were directly measured by high pressure liquid chromatography. Fast and slow acetylators show a similar half-life for sulfamethomidine (26 +/- 6 h) and its conjugates sulfamethomidine (26 +/- 6 h) and N4-acetylsulfamethomidine (36 +/- 16 h). Approximately 50-60% of the oral dose of sulfamethomidine is excreted in the urine, leaving 40-50% for excretion into bile and faeces. The main metabolite of sulfamethomidine is its N1-glucuronide, which accounts for 36 +/- 7% of the dose, followed by N4-acetylsulfamethomidine (16 +/- 8%). N1-glucuronidation results in a 75% decrease in protein binding of sulfamethomidine. N4-acetylsulfamethomidine and its N1-glucuronide showed the same high protein binding of 99%. The renal clearance of N4-acetylsulfamethomidine is 7.9 +/- 2.2 ml/min and approximately 20 times as high as that of the parent drug (0.46 +/- 0.16 ml/min). Total body clearance of sulfamethomidine is 4.5 +/- 0.9 ml/min and the volume of distribution in steady state 10.6 +/- 1.7 1. No measurable plasma concentrations of the N1-glucuronides from sulfamethomidine are found in plasma. This may be explained by renal glucuronidation after active tubular reabsorption.

Comparison of the metabolism of four sulphonamides between humans and pigs

Pigs are unable to form N1-glucuronides of sulphadimethoxine and sulphamethomidine, while humans are able to do so. Pigs and humans are able to oxidise sulphapyridine and form the O-glucuronide. The double conjugate N4-acetylsulphapyridine-O-glucuronide is formed in humans but not in pigs. Sulphadiazine is mainly acetylated in both humans and pigs. A hypothesis about N1-glucuronidation is presented.

Novel oxidative pathways of sulphapyridine and sulphadiazine by the turtle Pseudemys scripta elegans

The sulphonamides sulphapyridine and sulphadiazine show novel hydroxy metabolites in the turtle Pseudemys scripta elegans. In the excreta of the turtles the monohydroxy metabolites 4-hydroxy- and 5-hydroxysulphapyridine and the dihydroxy metabolite 4,5-dihydroxysulphapyridine were detected. Of sulphadiazine only dihydroxy metabolites 4,5- and 4,6-dihydroxysulphadiazine were detected. About 70-90% of the dose of sulphapyridine was recovered, while this figure varied between 48 and 69% for sulphadiazine.

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.

Pharmacokinetics, N1-glucuronidation and N4-acetylation of sulfadimethoxine in man

Sulfadimethoxine is metabolized by O-dealkylation, N4-acetylation and N1-glucuronidation. In man, only N1-glucuronidation and N4-acetylation takes place, leading to the final double conjugate N4-acetylsulfadimethoxine-N1-glucuronide. The N1-glucuronides are directly measured by high pressure liquid chromatography. When N4-acetylsulfadimethoxine is administered as parent drug, 30% of the dose is N1-glucuronidated and excreted. Fast acetylators show a shorter half-life for sulfadimethoxine than slow acetylators (27.8 +/- 4.2 h versus 36.3 +/- 5.4 h; P = 0.013), similarly the half-life of the N4-acetyl conjugate is also shorter in fast acetylators (41.3 +/- 5.2 h versus 53.5 +/- 8.5 h, P = 0.036). No measurable plasma concentrations of the N1-glucuronides from sulfadimethoxine are found in plasma. N1-glucuronidation results in a 75% decrease in protein binding of sulfadimethoxine. N4-acetylsulfadimethoxine and its N1-glucuronide showed the same high protein binding of 99%. Approximately 50-60% of the oral dose of sulfadimethoxine is excreted in the urine, leaving 40-50% for excretion into bile and faeces.