Chromatographic method for the simultaneous quantification of dapsone and clofazimine in nanoformulations.

The low bioavailability and nonspecific distribution of dapsone and clofazimine, commonly applied in combination for the treatment of leprosy, can produce toxic effects. Nanotechnological approaches enhance the delivery of these drugs. Therefore, a high-performance liquid chromatography method was developed for the simultaneous determination of dapsone and clofazimine loaded in nanoformulations for quality control purposes. Chromatographic separation was achieved on a reversed-phase Kinetex core-shell C18 column, followed by spectrophotometric detection at 280 nm. Considering the different physicochemical properties of dapsone and clofazimine, elution was performed in gradient mode using an aqueous acetate buffer (50 mmol/L, pH 4.8) and an increasing acetonitrile content from 27 to 63% v/v at a flow rate of 1.0 mL/min with retention times of 6.2 and 14.0 min, respectively. The method was validated according to the European Medicines Agency guideline and it was found to be specific, accurate (99.6-114.0%), and precise for intra- (RSD ≤ 1.8%) and interday assays (RSD ≤ 12.5%). Both drugs showed stability after 24 h at room temperature and over three freeze-thaw cycles with recoveries ≥86.2%. Low temperature (4°C) in the autosampler caused the precipitation of clofazimine and must be avoided. The validated method was successfully applied in the quantification of both drugs in nanoformulations.

Development and Characterization of Dapsone Cocrystal Prepared by Scalable Production Methods.

In this study, the formation of caffeine/dapsone (CAF/DAP) cocrystals by scalable production methods, such as liquid-assisted grinding (LAG) and spray drying, was investigated in the context of the potential use of processed cocrystal powder for pulmonary delivery. A CAF/DAP cocrystal (1:1 M ratio) was successfully prepared by slow evaporation from both acetone and ethyl acetate. Acetone, ethyl acetate, and ethanol were all successfully used to prepare cocrystals by LAG and spray drying. The powders obtained were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), thermogravimetry (TGA), and Fourier transform infrared spectroscopy (FTIR). Laser diffraction analysis indicated a median particle size (D50) for spray-dried powders prepared from acetone, ethanol, and ethyl acetate of 5.4 ± 0.7, 5.2 ± 0.1, and 5.1 ± 0.0 µm respectively, which are appropriate sizes for pulmonary delivery by means of a dry powder inhaler. The solubility of the CAF/DAP cocrystal in phosphate buffer pH 7.4, prepared by spray drying using acetone, was 506.5 ± 31.5 µg/mL, while pure crystalline DAP had a measured solubility of 217.1 ± 7.8 µg/mL. In vitro cytotoxicity studies using Calu-3 cells indicated that the cocrystals were not toxic at concentrations of 0.1 and of 1 mM of DAP, while an in vitro permeability study suggested caffeine may contribute to the permeation of DAP by hindering the efflux effect. The results obtained indicate that the CAF/DAP cocrystal, particularly when prepared by the spray drying method, represents a possible suitable approach for inhalation formulations with applications in pulmonary pathologies.

Flow injection chemiluminescence sensor using core-shell molecularly imprinted polymers as recognition element for determination of dapsone.

This paper reports the preparation of dapsone (DDS) imprinted polymer layer-coated silica submicron particles (SiO(2)) combined with chemiluminescence (CL) toward analysis of tracing DDS in practical samples. To induce the selective occurrence of surface polymerization, the amino groups were first grafted at the surface of SiO(2) by the (3-aminopropyl)triethoxysilane (APTES). The molecularly imprinted polymers (MIP) were coated at the surface of modified SiO(2) by the graft copolymerization. After the removal of templates, recognition sites of DDS were exposed in the polymer layers. The DDS-imprinted products were characterized by FT-IR, SEM, TEM, dynamic adsorption, and static adsorption tests. The proximity between the thickness of MIP layer and the spatial size of DDS indicated that the imprinted sites almost situated at the surface of MIP, leading to rapid adsorption saturation within 90 min. The apparent maximum binding amount of MIP toward DDS was evaluated as 14.98 mg·g(-1), which was much higher than that of non-molecularly imprinted polymers. The CL sensor provided a wide linear range for DDS within 1.0 × 10(-6) to 1.0 × 10(-4) mol·L(-1) with a detection limit of 5.27 × 10(-7) mol·L(-1) and the relative standard deviation of 1.8 % (n = 11) by determinations of 5.0 × 10(-6) mol·L(-1) DDS. This method was applied to determine DDS in urine samples and satisfactory results were obtained.

Spectrophotometric method for the determination of chromium (VI) in water samples.

A simple and sensitive spectrophotometric method for the determination of chromium has been developed. The method is based on the diazotization of Dapsone in hydroxylamine hydrochloride medium and coupling with N-(1-Napthyl) Ethylene Diamine Dihydrochloride by electrophilic substitution to produce an intense pink azo-dye, which has absorption maximum at 540 nm. The Beer's law is obeyed from 0.02-1.0 microg mL(-1) and the molar absorptivity is 3.4854 L mol(-1) cm(-1). The Limits of quantification and Limit of detection of the proposed method are 0.0012 microg mL(-1) and 0.0039 microg mL(-1) respectively. The method has been successfully applied for the determination of chromium in water samples and the results were statistically evaluated with that of the reference method.

Validation of a liquid chromatography-tandem mass spectrometry method for the simultaneous determination of sulfonamides, trimethoprim and dapsone in muscle, egg, milk and honey.

A quantitative multi-residue method that includes 13 sulfonamides, trimethoprim and dapsone was developed and validated according to Commission Decision 2002/657/EC for muscle, milk egg and honey samples. For all matrices, the same extraction procedure was used. Samples were extracted with an acetone/dichloromethane mixture and cleaned up on aromatic sulfonic acid (SO3H) SPE cartridges. After elution and concentration steps, analytes were identified and quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Data were acquired according to the multiple reaction-monitoring approach (MRM) and analytes were quantified both by the isotope dilution and the matrix-matched approaches calculating the response factors for the scanned product ions. The developed method shows good linearity, specificity, precision (repeatability and within-laboratory reproducibility), and trueness. Estimated CCß for sulfonamides ranged between 5.6 and 8.2 µg kg(-1) for eggs, between 11.1 and 69.9 µg kg(-1) for milk, between 64.7 and 87.9 µg kg(-1) for muscle, and between 2.7 and 5.3 µg kg(-1) for honey. CCß values for dapsone were 3.1, 0.6, 0.7 and 1.5 µg kg(-1) and for trimethoprim were 3.1, 6.7, 81.7 and 3.0 µg kg(-1) calculated for eggs, milk, muscle and honey, respectively. Recovery for all matrices was in the range from 89.1% and 109.7%. In matrix effect testing, no significant deviations were found between different samples of muscle and milk; however, a matrix effect was observed when testing different types of honey. The validation results demonstrate that the method is suitable for routine veterinary drug analysis and confirmation of suspect samples.

Feasibility of amlodipine besylate, chloroquine phosphate, dapsone, phenytoin, pyridoxine hydrochloride, sulfadiazine, sulfasalazine, tetracycline hydrochloride, trimethoprim and zonisamide in SyrSpend(®) SF PH4 oral suspensions.

The objective of this study was to evaluate the feasibility of 10 commonly used active pharmaceutical ingredients (APIs) compounded in oral suspensions using an internationally used suspending vehicle (SyrSpend(®) SF PH4 liquid): (i) amlodipine, (as besylate) 1.0mg/mL; (ii) chloroquine phosphate,15.0 mg/mL; (iii) dapsone, 2.0 mg/mL; (iv) phenytoin, 15.0 mg/mL; (v) pyridoxine hydrochloride, 50.0 mg/mL; (vi) sulfadiazine, 100.0 mg/mL; (vii) sulfasalazine, 100.0 mg/mL; (viii) tetracycline hydrochloride, 25.0 mg/mL; (ix) trimethoprim, 10.0 mg/mL; and (x) zonisamide, 10.0 mg/mL. All suspensions were stored both at controlled refrigeration (2-8 °C) and controlled room temperature (20-25 °C). Feasibility was assessed by measuring the percent recovery at varying time points throughout a 90-day period. API quantification was performed by high-performance liquid chromatography (HPLC-UV), via a stability-indicating method. Given the percentage of recovery of the APIs within the suspensions, the expiration date of the final products (API+vehicle) was at least 90 days for all suspensions with regard to both the controlled temperatures. This suggests that the vehicle is stable for compounding APIs from different pharmacological classes.

Identification and quantitation of impurities in dapsone preparations.

Chromatographic and fluorometric procedures were developed to isolate and quantitate small amounts of 2,4'-diamino-diphenyl sulfone and 4-aminodiphenyl sulfone in pharmaceutical preparations of the antileprosy drug 4,4'-diaminodiphenyl sulfone (dapsone). Identification was accomplished by comparison with authentic compounds employing UV absorption, fluorometry, and mass spectrometry in addition to TLC and high-pressure liquid chromatography.

High-speed liquid chromatographic analysis of dapsone and related compounds.

A nonaqueous solvent absorptive support system and an aqueous solvent reversed-phase support liquid chromatographic system for analysis of dapsone and related compounds were investigated. The absorptive support system was more suitable for analysis of dapsone in raw materials, formulations, and tissue residues. The suitability was judged by the relative selectivity, efficiency, precision, and sensitivity of the systems. The adsorptive support system was used for the analysis of trace amounts of raw material impurities and dapsone metabolites. Coupling fluorometric detection to the chromatographic system yielded a 10-pg on-column detection limit for dapsone; the UV detection limit was 250 pg.

Contaminants in commercial dapsone.

Three contaminants commonly found in commercial dapsone were identified as 2,4'-sulfonylbis(benzeneamine), 4-(phenylsulfonyl)benzeneamine, and 4-(4'-chlorophenylsulfonyl)benzeneamine. The identities were based on the spectral analysis and unambiguous synthesis of each compound. Solvent-free, pure dapsone was prepared by recrystallization from chloroform.

Electroanalysis of dapsone, an anti-leprotic drug.

The electrochemical oxidation and adsorption of dapsone, an anti-leprotic drug were studied in aqueous alcohol medium at a stationary glassy carbon electrode. Cyclic voltammetry studies showed one well-defined oxidation peak in the potential range 1.2-1.9 V at pH conditions 1.0, 4.0, 7.0, 9.2 and 13.0. The oxidation was irreversible and exhibited diffusion controlled adsorption. Controlled potential coulometry revealed one electron oxidation of the amino group in the molecule. A systematic study of the experimental parameters that affect the squarewave stripping response was carried out and the optimized experimental conditions were arrived at. A calibration plot was derived for the determination of the compound in solution. This method was used for the determination of dapsone in tablets and urine. The limits of determination was 0.0036 and 3.56 mg/ml and the relative standard deviation (n=10) was 4 ppt (0.4%) at a concentration level 0.100 mg/ml.

A spectrophotometric method for the determination of metoclopramide HCl and dapsone.

A rapid, sensitive and selective spectrophotometric method has been developed for the quantitative determination of metoclopramide hydrochloride (MCP) and dapsone (DAP) in both pure and dosage forms. The method is based on the diazo coupling reaction of the drugs with a new coupling agent, dibenzoyl methane in an alkaline medium. The resulting coloured azo dyes exhibit maximum absorption at 440 nm for MCP and at 470 nm for DAP with a molar absorptivity of 2.85x10(4) and 1.71x10(4) l mol(-1) cm(-1) for MCP and DAP, respectively. All variables have been optimized. No interferences were observed from excipients and the validity of the method was tested against reference method.

Simultaneous determination of dapsone and pyrimethamine by derivative spectrophotometry in pharmaceutical formulations.

A simple and fast method was developed for the simultaneous determination of dapsone and pyrimethamine by first-order digital derivative spectrophotometry. Acetonitrile was used as a solvent to extract the drugs from the pharmaceutical formulations, and the samples were subsequently evaluated directly by digital derivative spectrophotometry. The simultaneous determination of both drugs was performed by the zero-crossing method at 249.4 and 231.4 nm for dapsone and pyrimethamine, respectively. The best signal-to-noise ratio was obtained when the first derivative of the spectrum was used. The linear range of determination for the drugs was from 6.6 x 10(-7) to 2.0 x 10(-4) and from 2.5 x 10(-6) to 2.0 x 10(-4) mol/L for dapsone and pyrimethamine, respectively. The excipients of commercial pharmaceutical formulations did not interfere in the analysis. Chemical and spectral variables were optimized for determination of both analytes. A good level of repeatability, 0.6 and 1.7% for dapsone and pyrimethamine, respectively, was observed. The proposed method was applied for the simultaneous determination of both drugs in pharmaceutical formulations.

An improved bioassay for the qualitative detection of sulphonamide and dapsone residues.

An improved method of bioassay has been described for qualitative detection of sulphonamide and dapsone residues in kidney, muscle, urine, and milk. The sensitivity to the sulphonamides tested ranged from 0.01 to 0.3 micrograms/ml or g of tissue and from 0.003 to 0.0006 micrograms/ml for dapsone. No extraction procedures are needed.

Spectrophotometric determination of dapsone in pharmaceutical products using sodium 1,2-naphthoquinone-4-sulfonic as the chromogenic reagent.

Spectrophotometric determination of dapsone is described. The dapsone reacts with sodium 1,2-naphthoquinone-4-sulfonic in pH 6.98 buffer solution to form a salmon pink compound, and its maximum absorption wavelength is at 525 nm, epsilon525=3.68 x 10(4) l mol(-1) cm(-1). The absorbance of dapsone from 0.40 to 10 microg ml(-1) obeys Beer's law. The linear regression equation of the calibration graph is C=0.2334 A + 0.01288, with a linear regression correlation coefficient of 0.9998, the detection limit is 0.24 microg ml(-1), and recovery is from 99.2 to 102.4%. Effects of pH, surfactant, organic solvents, foreign ions, and standing time on the determination of dapsone have been examined. This method is simple and can be used for the determination of dapsone in injection solution of dapsone. The results obtained by this method agreed with those by the official method (dead-stop titration method [The Chinese Pharmacopoeia, Pharmacopoeia Commission, Ministry of Health, vol. 2, fifth ed., PRC Chemical Industry Press, Beijing, 2000, p.720]).

Spectrophotometric determination of dapsone by using 9-chloroacridine as a chromogenic reagent.

A spectrophotometric method for the quantitative determination of dapsone (1) has been developed through a condensation reaction of 9-chloroacridine as a chromogen and the amino groups of 1. The reaction variables were investigated and optimized. The resultant colored products is stable and was synthesized. The application of the present method to the determination of 1 in commercial tablets gave satisfactory results and was compared with the official methods. The proposed method ist simple, sensitive, reproducible and accurate.

Intracellular localization of dapsone and rifampicin in skin and nerve of multidrug treated leprosy patients.

Intracellular localization of antileprosy drugs dapsone (DDS) and rifampicin (RFP) was carried out on skin and nerve lesions obtained from multidrug treated, multi (BL-LL)- and pauci (BT-TT) bacillary cases of leprosy using immunocytochemical techniques. Intracellular localization of the above drugs especially in macrophages and Schwann cells was aimed by using rabbit raised anti DDS and RFP polyclonal antibody in an indirect peroxidase assay. Our study records both intra and extracellular staining with anti DDS and RFP antibodies in the skin as well as nerve lesions of MB and PB cases treated with MDT. All the nerves under investigation had moderate to severe pathology and hence free diffusion of the drug could be attributed to the broken barrier. Basal lamina around the Schwann cell did not seem to form a barrier. It was also noted that the drug (metabolite) persisted over a long period of time).

[The occurrence of sulfa residues in unpasteurized farm milk]. / Het voorkomen van 'sulfa'-residuen in rauwe boerderij(tank)melk.

The results of studies in 1984 and 1985 on the incidence of residues of sulphonamides in raw tank milk showed that, from 2 to 11 per cent milk was contaminated with Dapsone in the Netherlands. In 1984 sulphadimidine was found to be present in approximately six per cent of the samples of tank milk. In 1985, residues of Dapsone were detected, in approximately six per cent of the milk destined for consumption.

[The occurrence of dapsone residues following a one-time oral, intramuscular and intramammary application in healthy dairy cows]. / Het voorkomen van Dapson-residuen na éénmalige orale, intramusculaire en intramammaire toepassing bij gezonde melkrunderen.

Dapsone is frequently used as a bacteriostatic drug in the treatment of mastitis, endometritis and footrot (necrotic pododermatitis). The farmer usually obtains this drug by 'non-ethical' channels. A regular scheme of checking the milk for residues of sulphonamides will be introduced in 1986. The sensitivity of the test is approximately 25 ppb for Dapsone. This will result in lower milk price in the case of positive tests. In healthy animals, it is shown that intramuscular treatment with 35 grammes (+/- 70 mg/kg-1 body weight) of Dapsone results in residues of Dapsone and its metabolite monoacetyldapsone above this detection level for more than 6 1/2 days. Within 5 days after oral treatment with 48.75 grammes (+/- 100 mg/kg-1 body weight) and 2 1/2 days after single intramammary treatment with 0.8 grammes, the concentrations of residues detected dropped below 25 ppb. The other well-known metabolite diacetyldapsone was only present in detectable quantities in the first milkings after oral treatment.

Determination of dapsone in muscle tissue and milk using high-performance liquid chromatography-tandem mass spectrometry.

A precise and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of dapsone in muscle tissue and milk has been developed. The sample preparation was based on extraction with organic solvent and automated solid-phase extraction (SPE) cleanup. At least three product ions were monitored for the analyte. The method was validated according to the European Decision 2002/657/EC. Estimated analytical limits were 0.0018 ng/g for CCα and 0.0031 ng/g for CCß in meat and milk. An excellent linear concentration range was observed for both matrices with a correlation coefficient better than 0.997. Recoveries were 105-117% in meat and 101-108% in milk, with satisfactory precision and coefficients of variance (CV) less than 8%. Additionally, a simplified quantification approach was successfully evaluated depending only on the response factor (F) without the use of calibration curve. The developed method provides reliable and sensitive identification and quantification of dapsone in meat and milk.

Development of a liquid chromatography­tandem mass spectrometry method for the determination of sulfonamides, trimethoprim and dapsone in honey and validation according to Commission Decision 2002/657/EC for banned compounds [corrected].

This work reports a sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for identification and quantification of seven sulfonamides, trimethoprim and dapsone in honey. The method is based on a solid-phase extraction (SPE) step of the target analytes with Oasis HLB cartridges after acidic hydrolysis of the honey sample to liberate the sugar-bound sulfonamides. Analysis was performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the positive electro-spray ionization (ESI) mode with two different isotopically labeled internal standards with the view to improve the quantitative performance of the method. The method validation has been performed according to the Commission Decision 2002/657/EC; the average recoveries, measured at three concentration levels (1.5, 2.5 and 5.0 µg kg(-1)), have been estimated in the range 70 to 106% while the respective % relative standard deviations of the within-laboratory reproducibility ranged from 6 to 18%. Mean values of the expanded uncertainties calculated were in the range 22-41% at the 99% confidence level. Decision limit (CCα) and detection capability (CCß) values were in the ranges 0.4-0.9 and 0.7-1.4 µg kg(-1), respectively. Matrix effects have been investigated demonstrating a moderate signal suppression/enhancement for most of the target compounds. The method described has been successfully applied to the analysis of honey samples; sulfamethoxazole, sulfathiazole and trimethoprim were detected in some cases.