Comparison of the metabolism of four sulphonamides between humans and 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.

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.

Shedding light on minipig drug metabolism - elevated amide hydrolysis in vitro

1. In recent years, the minipig is increasingly used as a test species in non-clinical assessment of drug candidates. While there is good scientific evidence available concerning cytochrome P450-mediated metabolism in minipig, the knowledge of other metabolic pathways is more limited. 2. The aim of this study was to provide an understanding of when, why, and how drug metabolism in minipig differs from other species commonly used in non-clinical studies. In-house cross-species metabolite profile comparisons in hepatocytes and microsomes of 38 Roche development compounds were retrospectively analyzed to compare the metabolism among minipig, human, rat, dog, monkey, rabbit and mouse. 3. A significant contributor to the elevated metabolism observed for certain compounds in minipig was identified as amide hydrolysis. The hepatic amide hydrolysis activity in minipig was further investigated in subcellular liver fractions and a structure-activity relationship was established. When structural motifs according to the established SAR are excluded, coverage of major human metabolic pathways was shown to be higher in minipig than in dog, and only slightly lower than in cynomolgus monkey. 4. A strategy is presented for early identification of drug compounds which might not be suited to further investigation in minipig due to excessive hydrolytic metabolism.

Structural elucidation of sulfaquinoxaline metabolism products and their occurrence in biological samples using high-resolution Orbitrap mass spectrometry

Four previously unreported metabolism products of sulfaquinoxaline (SQX), a widely used veterinary medicine, were isolated and analyzed using liquid chromatography coupled to high-resolution Orbitrap mass spectrometry. Metabolites were structurally elucidated, and a fragmentation pathway was proposed. The combination of high-resolution MS(2) spectra, linear ion trap MS(2), in-source collision-induced dissociation (CID) fragmentation, and photolysis were used to analyze SQX and its metabolites. All metabolism products identified showed a similar fragmentation pattern to that of the original drug. Differential product ions were produced at m/z 162 and 253 which contain the radical moiety with more 16 Da units than sulfaquinoxaline. This occurs by a hydroxyl attachment to the quinoxaline moiety. With the exception of two low-intensity compounds, all the mass errors were below 5.0 ppm. The distribution of these metabolites in some animal species are also presented and discussed.

IDENTIFICATION OF CYTOCHROME P450 AND ARYLAMINE N-ACETYLTRANSFERASE ISOFORMS INVOLVED IN SULFADIAZINE METABOLISM

Sulfadiazine hydroxylamine has been postulated to be the mediator of the greatly increased rates of adverse reactions to sulfadiazine experienced by people with human immunodeficiency virus infection. Therefore, we investigated the in vitro human cytochrome P450 (P450) and N-arylamine acetyltransferase (detoxification) metabolism of sulfadiazine. Formation of both the hydroxylamine and 4-hydroxy sulfadiazine was NADPH-dependent in human liver microsomes (HLM). The average K(m) (+/-S.D.) and V(max) in HLM (n = 3) for hydroxylamine formation was 5.7 +/- 2.2 mM and 185 +/- 142 pmol/min/mg, respectively. Significant (p < 0.05) inhibition by selective P450 isoform inhibitor sulfaphenazole (2.1 microM; CYP2C9) indicated a role for CYP2C9 in the formation of the hydroxylamine. Hydroxylamine formation correlated strongly with tolbutamide 4-hydroxylation (CYP2C8/9) in HLM (r = 0.76, p < or = 0.004, n = 12). Fluconazole (CYP2C9/19 and CYP3A4 inhibitor at clinical concentrations) inhibited hydroxylamine formation, with one-enzyme model K(i) estimates ranging from 9 to 40 microM. Acetylation of sulfadiazine in human liver cytosol (HLC) correlated strongly with NAT2 activity as measured by sulfamethazine N-acetylation (r = 0.92, p < 0.001, n = 12). The average K(m) (+/-S.D.) and V(max) in HLC (n = 3) was 3.1 +/- 1.7 mM and 221.8 +/- 132.3 pmol/min/mg, respectively. The polymorphic acetylation of sulfadiazine may predispose slow acetylator patients to adverse reactions to sulfadiazine. On the basis of our K(i) estimates, clinical fluconazole concentrations of 25 microM would produce decreases of 40 to 70% in hepatic-mediated hydroxylamine production. Therefore, we predict that fluconazole may prove useful in the clinic as an in vivo inhibitor of sulfadiazine hydroxylamine formation to suppress adverse reactions to this drug.

Metabolism of 14C-sulphadimethoxane in swine

1. 14C-sulphadimethoxine (4-amino-N-(2,6-dimethoxy-4-pyrimidinyl)benzene-[U-14C]-sulphonamide; 14C-SDM) was given orally (60 mg/kg body weight) to eight swine (weight 27-32 kg). Urine and faeces were collected from 0 to 72 h after dosing and tissue samples were collected from animals exsanguinated at 12, 24, 48 and 72 h after dosing. The concentration of total 14C-labelled residues (14C-SDM equivalents) in tissues other than the gastrointestinal tract ranged from 99-1 ppm (plasma) to 13.8 ppm (adipose tissue) 12 h after dosing. Seventy-two hours after dosing tissue concentrations ranged from 5.4 ppm (plasma) to 0.5 ppm (skeletal muscle). The concentration in the large intestine was substantially higher (10.4 ppm) than in the stomach (2.8 ppm) and small intestine (1.4 ppm) 72 h after dosing. 2. Of the 14C, 77% was excreted in the urine from 0 to 72 h after dosing with 14C-SDM, mostly in the 0-24-h collection. Fifteen percent was excreted in the faeces from 0 to 72 h after dosing, with most of this occurring 36-72 h post-dosing. 3. 14C-SDM accounted for 24% (liver) to 66% (adipose tissue) and the N4-acetyl derivative of SDM (N4-Ac-SDM) accounted for 10% (skeletal muscle) to 35% (kidney) of the total 14C in the tissues 12 h after dosing. The N4-glucose conjugate of SDM (G-SDM) was a major 14C-labelled compound in skeletal muscle (21% of total) and liver (28%) but it was not detected in adipose tissue or kidney. The N4-glucuronic acid conjugate of SDM (GA-SDM) was a minor metabolite in kidney, but was not detected in other tissues collected 12 h after dosing. Desamino SDM was a minor metabolite in the kidney. A minor metabolite in plasma was identified as the sulphate ester of 3-hydroxysulphadimethoxine. 4. 14C-labelled fractions isolated from 0 to 6-h urine included N4-Ac-SDM (82%), SDM (3%) and GA-SDM (6%).