Penetration monitoring of drugs and additives by ATR-FTIR spectroscopy/tape stripping and confocal Raman spectroscopy - A comparative study.

Vibrational spectroscopy is a useful tool for analysis of skin properties and to confirm the penetration of drugs and other formulation compounds into the skin. In particular, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and confocal Raman spectroscopy (CRS) have been optimised for skin analysis. Despite an impressive amount of data on these techniques, a comparative methodological assessment for skin penetration monitoring of model substances is still amiss. Thus, in vitro skin penetration studies were conducted in parallel using the same porcine material and four model substances, namely sodium laureth sulfate (SLES), sodium dodecyl sulfate (SDS), sulfathiazole sodium (STZ) and dimethyl sulfoxide (DMSO). ATR-FTIR spectroscopy in combination with tape stripping and CRS were employed to evaluate the skin penetration of the applied substances. In addition, the skin hydration status or change in skin hydration after application was investigated. The results show that both methods provide valuable information on the skin penetration potential of applied substances. The penetration profiles determined by CRS or ATR-FTIR/tape stripping were comparable for all substances; a slow decrease in relative substance concentration was visible from the skin surface inwards within the stratum corneum (SC). In general, deeper penetration into the SC was observed with CRS, which may be related to the depth resolution of the employed device. However, when related to the respective total SC thickness of each experiment, the penetration depths determined by parallel CRS and ATR-FTIR analysis were in good agreement for all model substances. The observed order of the penetration depth was DMSO > SDS > SLES > STZ with both techniques. A decrease of the relative concentration to 10% of the maximum value was found approximately between 34 and 89% of total SC thickness. Summarising these findings, advantages and drawbacks of the two techniques for in vitro skin penetration studies are discussed.

Structural characterization of new Schiff bases of sulfamethoxazole and sulfathiazole, their antibacterial activity and docking computation with DHPS protein structure.

New Schiff bases (1, 2) of substituted salicylaldehydes and sulfamethoxazole (SMX)/sulfathiazole (STZ) are synthesized and characterized by elemental analysis and spectroscopic data. Single crystal X-ray structure of one of the compounds (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(5-methylisoxazol-3-yl)benzenesulfonamide (1c) has been determined. Antimicrobial activities of the Schiff bases and parent sulfonamides (SMX, STZ) have been examined against several Gram-positive and Gram-negative bacteria and sulfonamide resistant pathogens; the lowest MIC is observed for (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(thiazol-2-yl)benzene sulfonamide (2c) (8.0 µg mL(-1)) and (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(5-methylisoxazol-3-yl)benzene sulfonamide (1c) (16.0 µg mL(-1)) against sulfonamide resistant pathogens. DFT optimized structures of the Schiff bases have been used to carry out molecular docking studies with DHPS (dihydropteroate synthase) protein structure (downloaded from Protein Data Bank) using Discovery Studio 3.5 to find the most preferred binding mode of the ligand inside the protein cavity. The theoretical data have been well correlated with the experimental results. Cell viability assay and ADMET studies predict that 1c and 2c have good drug like characters.

Serum activity/concentration profiles of a sustained-released formulation of sulphathiazole-trimethoprim (2.5:1) in calves.

Thirty-six two-week-old healthy Holstein-Friesian calves weighing between 52 and 58 kg were divided at random into three groups of 12; group A calves were given a single oral bolus containing 2.5 g sulphathiazole and 1 g trimethoprim in a sustained-release formulation; group B received the same doses of the drugs but the trimethoprim was not in a sustained-release formulation; group C received a bolus containing 2.5 g sulphathiazole and 0.5 g conventional trimethoprim. Blood samples were collected at intervals for two days, the serum was separated and the composite antibacterial activity profiles of the mixture were analysed by an agar-diffusion microbiological method. The mean maximum activities in the serum of the three groups were 23.4 microg/ml in group A, 9.25 microg/ml in group B and 8.01 microg/ml in group C. The mean areas under the curves of the serum activity time curves were 838 microg/ml/hour in group A, 216 microg/ml/hour in group B and 182 microg/ml/hour in group C.

Release characteristics of pectin microspheres prepared by an emulsification technique.

The potential application of pectin as a matrix polymer for making microspheres by an emulsification technique was explored, and the drug release property of these pectinate microspheres containing drug cores of varying aqueous solubilities: sulphanilamide, sulphaguanidine and sulphathiazole, was investigated using different dissolution media. The size and size distribution, specific surface area, drug content and drug release property of the pectinate microspheres were determined. The solubility and solution pH of drugs and their propensity to interact with pectin were characterized. Pectinate microspheres were successfully prepared by external gelation, using a modified emulsification technique. The kinetics of drug release from the microspheres best fitted Higuchi's model. Interestingly, the lowest percentage of drug released was produced by microspheres which were smallest in size and, therefore, largest in specific surface area, and containing sulphanilamide, the most aqueous soluble and the lowest molecular weight drug. Mathematical correlation study indicated that the drug release profile of pectinate microspheres was notably affected by the drug content and the extent of drug-pectin interaction in the microspheres. Generally, a higher percentage of drug was released from the microspheres with a higher drug content and/or lower extent of drug-pectin interaction. The extent of drug-pectin interaction was highest in microspheres containing sulphanilamide, followed by sulphaguanidine and sulphathiazole, opposite to that of drug content.

Polyphosphazene membranes and microspheres in periodontal diseases and implant surgery.

Membranes or microcapsules made from polyphosphazenes bearing amino acid side groups are proposed for the treatment of periodontal diseases. Polyphosphazene membranes, prepared with alanine ethyl ester and imidazole in the molar ratio of 80:20 as phosphorus substituents, gave a degradation rate that corresponded to the healing of the bone defect. These membranes were much more successful in promoting healing of rabbit tibia defects than polytetrafluoroethylene membranes. Antibacterial or anti-inflammatory drugs, useful in periodontal tissue regeneration, could be entrapped in the polyphosphazene membranes and released both in vitro and in vivo at a rate that ensured therapeutic concentrations in the surrounding tissue. Polyphosphazene microspheres, prepared with phenylalanine ethyl ester as a phosphorus substituent and loaded with succinylsulphathiazole or naproxen, were also obtained. The kinetics of release from these matrices were very convenient in yielding local concentrations of the two drugs that are useful per se or when mixed with hydroxyapatite for better bone formation.

Effects of drug solubility, drug loading, and polymer molecular weight on drug release from Polyox tablets.

This study investigated the effects of polymer molecular weight, drug solubility, addition of a water-soluble excipient, and drug loading on zero-order release kinetics and elucidated the release mechanism of a drug from directly compressed tablets. Directly compressed tablets consisting of polyethylene oxides (PEO) (MW = 0.9, 2.0 and 4.0 x 10(6)) and drugs (solubility ranging from 290 to 25,000 mg/l) were formulated with or without a water-soluble excipient (lactose). For PEO tablets (MW = 0.9 x 10(6)), drug release is primarily swelling/erosion controlled for drugs for which solubility is below 1%, resulting in zero-order release kinetics. For PEO tablets (MW = 4.0 x 10(6)), drug release is controlled at a zero-order rate by the dissolution rate of the drug at high loading (39%). At low loading (20%), drug diffusion through the swollen gel layer becomes the governing release mechanism. For a highly water-soluble drug (e.g., diclofenac Na), drug diffusion is the controlling mechanism regardless of the molecular weight of the PEOs. Zero-order release kinetics can be achieved with PEO tablets (MW = 0.9 x 10(6)) for drugs for which solubility is below 1%. PEO tablets (MW = 2.0 x 10(6)) provided zero-order release for poorly water-soluble drugs (below 0.2%) at 39% drug loading. It is possible to attain zero-order release kinetics with PEO tablets (MW = 4.0 x 10(6)) using a drug which has a solubility of less than 0.1%.

Water-soluble polycations as oral drug carriers (tablets).

New bioerodible materials that are noncross-linked and water-soluble copolymers of trimethylaminoethyl methacrylate chloride (TMAEMC) and methyl methacrylate (MMA) were synthesized and then bound to anionic drugs (diclofenac Na and Na sulfathiazote) to form water-insoluble complexes. These drug-polymer complexes release the bound drugs only in ionic media. Compressed tablets were prepared from these anion-exchange resins, and their release profiles follow zero-order kinetics (n > 0.89, where n is the release exponent). The effects of various excipients (dextrose, lactose, and microcrystalline cellulose) were studied, and the polymer composition was found to influence the duration of drug release. It was also found that the release of anionic drugs from drug-PTMAEM/MMA is linear and that it is possible to "tailor-make" their release kinetics by suitably altering the copolymer composition. When a high content of a water-insoluble excipient (i.e., microcrystalline cellulose) was used to fabricate the tablets, the release kinetics deviated from linearity (n = 0.73). In general, release kinetics were well described by a dissociation/erosion mechanism. Drug loading could be increased by increasing the exchange capacity of the polymer (i.e., by increasing the content of the quaternary amine monomer).

Deposition kinetics, metabolism and urinary excretion of sulfathiazole following oral administration in sheep.

Deposition kinetics, metabolism and urinary excretion of sulfathiazole were investigated in German black head sheep following single oral administration (100 mg/kg). Kinetic evaluation of plasma levels was performed using a two-compartment best fit model. Sulfathiazole is significantly metabolized to N4-acetyl metabolite in the rumen fluid. The drug is very poorly absorbed since the minimum effective concentration in plasma was not attained at any time following oral administration. The prolonged elimination half-life in sheep may be due to a low rate of drug absorption from the rumen and gastro-intestinal tract. Sulfathiazole was mainly excreted in the urine as free drug and N4-acetyl metabolite.

Oral bioavailability of sulphamethoxydiazine, sulphathiazole and sulphamoxole in dwarf goats.

To get a better insight into the oral bioavailability of sulphonamides in ruminants, sulphamethoxydiazine (pKa 7.0), sulphathiazole (pKa 7.2), and sulphamoxole (pKa 7.4) were administered to dwarf goats (n = 5). The drugs were given at 2-week intervals by the intravenous or intraruminal route at a dose of 100 mg per kg body weight. After IV injection, the mean half-life (t1/2 beta in h +/- SEM) was 0.80 +/- 0.10 h, 2.35 +/- 0.38 h, and 3.36 +/- 1.25 h, for sulphathiazole, sulphamoxole, and sulphamethoxydiazine, respectively and the mean distribution volume (Vd beta) was 0.23 +/- 0.05 l/kg, 0.23 +/- 0.04 l/kg, and 0.33 +/- 0.02 l/kg. After intraruminal administration, the mean bioavailability varied from 86.0 +/- 11.8% for sulphamethoxydiazine to 46.6 +/- 4.3% for sulphamoxole, and 52.6 +/- 7.2% for sulphathiazole. The elimination half-life was significantly prolonged, probably due to a low rate of drug absorption from the gastrointestinal tract. In contrast to chloramphenicol, the sulphonamides studied were stable when incubated in rumen fluid at 39 degrees C.

Phthalylsulphathiazole in rheumatoid arthritis.

Sixteen patients with active rheumatoid arthritis were treated with phthalylsulphathiazole (4 g/day) over a period of 24 weeks. Although there was some statistically significant improvement in plasma viscosity, IgM, pain score, morning stiffness and summated change score, this was either intermittent or not maintained. Five patients withdrew from the trial before completion, four (25%) with non-serious adverse reactions and one patient from lack of efficacy; only one patient elected to remain on the drug beyond the 24-week period. Low free and total sulphathiazole serum concentrations were found, confirming that most of the drug remained within the gut. This investigation suggests, certainly at the dose used, that phthalylsulphathiazole does not have the properties of a second-line agent. Higher doses of the drug will not be ethically feasible.

Effect of Haemonchus contortus infection on the clearance of antipyrine, sulfobromophthalein, chloramphenicol, and sulfathiazole in lambs.

A study was made to determine the effect of Haemonchus contortus parasitic infection in lambs on the clearance of several IV administered drugs. Clearance of sulfobromophthalein or sulfathiazole from the plasma of lambs was unaffected by infection with H contortus. Clearance of antipyrine was enhanced by the infection, and thiabendazole treatment did not alter this effect. Clearance of chloramphenicol (CAP), administered as the succinate ester (CAPS), was not changed by the infection, but it was increased after treatment with thiabendazole. Changes in the mean body residence time and initial plasma concentration of CAPS and CAP after treatment with thiabendazole indicate that hydrolysis of CAPS to CAP was reduced. High concentrations of CAPS apparently enhanced its own elimination directly rather than via the expected sequence involving hydrolysis, glucuronidation, and excretion of CAP-glucuronide. Enhanced clearance of antipyrine following infection of lambs with H contortus can be explained in at least 2 ways. First, it is possible that the lambs did not have mature amounts of hepatic drug metabolizing enzyme activity as reported by other investigators, which may be explained by breed differences or animal husbandry practices. Second, infection of lambs by H contortus may have triggered an inductive response in hepatic cytochrome P-450-mediated activities, which might result via a generalized enhancement in hepatic protein synthesis associated with the physiologic response to replace plasma proteins and other blood components lost through gastrointestinal hemorrhage caused by the active feeding of adult worms. Other phase-II reactions such as acetylation, glucuronidation, and glutathione-S-transferase apparently were not affected.

Effect of iodopyracet on renal excretion of sulfamethizole in rabbits.

To predict quantitatively drug interaction kinetics from the single-drug clearance studies, we examined the effect of iodopyracet (IOD) on sulfamethizole (SMZ) excretion in rabbits. Even though the decline of systemic IOD plasma concentration was linear, the renal clearance of SMZ decreased significantly in the presence of IOD. The results could be described by a perfusion model incorporated with the competitive inhibition for tubular secretion. For IOD with a high extraction ratio, it was suggested that a heavy load of the drug was supplied to the sites of secretion and caused the saturation of transport systems, even though the renal excretion kinetics were apparently linear in respect to the systemic circulation. These facts indicated that a linear relationship between the concentrations in the systemic circulation and at the sites of tubular secretion can not always be presumed. Consequently, SMZ-IOD interaction study stressed the importance of the drug concentrations at the sites of interaction for quantitative elucidation of drug-drug interactions.

Kinetic studies on drug disposition in rabbits. II. Dose dependent pharmacokinetics of sulfamethizole.

In order to evaluate dose-dependent sulfamethizole (SMZ) kinetics, 100, 300 and 1000 mg of SMZ was constantly infused over 5 min in rabbits and thereafter plasma and urine samples were collected at convenient intervals. When a dose of 100 mg was given, the time course of total plasma concentration followed a biexponential characteristic. For higher doses, plasma decay curves revealed a convex descending feature after the distribution phase. The respective unbound fraction in plasma (fp) at the total plasma concentrations of 200 and 100 micrograms/ml were 0.41 and 0.19. The corresponding total body clearances were 2.6 and 2.2 l/h, indicating that the drug elimination did not contribute to the convex-descending plasma curves. A physiologically based pharmacokinetic model was adapted to various tissue levels of SMZ. No saturable tissue binding was observed and the apparent volume of distribution of SMZ at steady state with a rabbit of 3.3 kg, Vss (1), calculated by tissue volumes and partition coefficients of tissue to unbound plasma was expressed as follows: Vss = 0.14 + 1.86fp. From this relationship, it was shown that the apparent volume of distribution of SMZ was significantly affected by the unbound fraction in plasma and the dose-dependent kinetics after intravenous administration was due to the decrease of the apparent volume of distribution with time. The tissue distribution study contributed significantly to the understanding of the dose-dependent drug kinetics.

Kinetic studies on drug disposition in rabbits. III. Effect of tolbutamide on renal excretion of sulfamethizole.

The effect of tolbutamide (TB) on the urinary excretion of sulfamethizole (SMZ) under constant infusion of SMZ at 100 mg/h was studied. Intravenous administration of TB (50 mg/kg) caused a decrease in the urinary excretion rate of SMZ but an increase in the unbound concentration of SMZ in plasma. The total concentration of SMZ in plasma decreased rapidly after TB injection and then increased gradually to a level higher than the control. The slope of the terminal phase of the unbound concentration of TB in plasma in the presence of SMZ was significantly smaller than that of TB alone. The analysis using the perfusion limited model showed that the elimination kinetics of SMZ in the presence of TB could be described by the mutual displacement of plasma protein binding of both drugs and the competitive inhibition of the tubular secretion of SMZ by the unbound concentration of TB in renal vein. Further the inhibitor constant was in good agreement with that for the in vitro uptake by renal cortex slices.

Kinetic studies on drug disposition in rabbits. I. Renal excretion of iodopyracet and sulfamethizole.

In order to quantify the renal handling of iodopyracet (IOD) and sulfamethizole (SMZ), single-drug clearance studies in rabbits were performed under quasi-steady state conditions with stepwise increasing the infusion rate of IOD or SMZ. Although concentration dependence of plasma protein binding was observed for both drugs, the urinary excretion rate of IOD was proportional to its total plasma concentration at low total plasma concentrations of 0.05-0.8 mM. On the other hand, the relationship between urinary excretion rate and total plasma concentration of SMZ was a concave-ascending curve at low plasma concentrations and the renal clearance of SMZ was sensitive to changes in plasma protein binding. However, renal clearances referenced to unbound plasma concentration at total plasma concentrations of 0.05 mM for IOD and SMZ were 9.5 and 38 l/h, respectively. Those values were much greater than the effective plasma flow in rabbits. These facts indicated that the intrinsic clearances at the sites of tubular secretion were high and that the rates of secretion were fully or partially limited by the renal plasma flow. Furthermore it was suggested that unbound drug was liberated from plasma protein at the sites of tubular secretion. The data obtained at high plasma concentrations indicated that the tubular secretion of IOD had capacity limited characteristics and that the urinary excretion of SMZ involved tubular reabsorption as well as saturable tubular secretion. From the data obtained, a perfusion-limited pharmacokinetic model was constructed characterizing the excretory processes, namely, glomerular filtration, passive tubular reabsorption, saturable tubular secretion and reequilibrium between bound and unbound drugs in plasma. For both drugs, the estimates for bulk flow rate were reasonable values of effective renal plasma flow and the dissociation constants for tubular secretion agreed well with those for in vitro renal cortex accumulation, suggesting that the kinetic model based on physiological concepts was useful for the understanding of the drug elimination processes.

Removal of sulfonamides by hemofiltration.

Hemofiltration is a relatively new technique for removing toxic substances from the body. Unlike hemodialysis or hemoperfusion, the driving force behind hemofiltration is ultrafiltration. There have been several studies examining the clearance of drugs by hemofiltration but to date no study has investigated in a systematic way the effects of protein binding, perfusate flow, transmembrane pressure, and the duration of treatment on drug clearance by hemofiltration. The influence of these factors on the hemofiltration clearance of three sulfonamides with differing degrees of protein binding was investigated. It was found that hemofiltration drug clearance decreased with the duration of hemofiltration and protein binding but increased with perfusate flow and transmembrane pressure.

Effect of the interaction of drug-beta-cyclodextrin complex with bile salts on the drug absorption from rat small intestinal lumen.

This investigation was concerned with the change of the bioavailability of a drug owing to the interaction of the drug-beta-cyclodextrin complex with bile salts in rat intestinal lumen. The absorption of sulfamethizole (SMZ) from rat intestinal lumen after administration of SMZ-beta-cyclodextrin complex was determined by a closed-loop method in the presence or absence of bile. The blood level of SMZ after administration of SMZ-beta-cyclodextrin complex was significantly decreased in comparison with that after administration of SMZ alone in bile duct-ligated rats. On the other hand, the blood level of SMZ after SMZ-beta-cyclodextrin administration in intact rats (bile duct non-ligated) or on the addition of sodium cholate was similar to the level in the case of SMZ alone. Thus, bile salts were found to act as a competing agent in the gastrointestinal tract.

[The relation of the acetylation phenotype to the predisposition to typhoid fever and its clinical course]. / Sviaz' fenotipa atsetilirovaniia s predraspolozhennost'iu k briushnomu tifu i ego klinicheskim techeniem.

Altogether 33 typhoid fever convalescents and 36 contacts of a control group were examined during an epidemic outbreak. In one year 17 former patients and 65 controls (persons who had been at the center of the outbreak but contracted no disease) were examined. Norsulfazole was used as a model agent to study an acetylation phenotype. Unimodal distribution of a degree of norsulfazole distribution was noted in the convalescents, bimodal distribution in the controls and patients examined in one year. Persons with a rapid type of acetylation were more predisposed to typhoid fever, and intoxication in them was more noticeable.