Column and thin-layer chromatographic methods for the simultaneous determination of acediasulfone in the presence of cinchocaine, and cefuroxime in the presence of its hydrolytic degradation products

Column liquid chromatography (LC) and thin-layer chromatography (TLC)-densitometry methods are described for simultaneous determination of acediasulfone (Ace) and cinchocaine (Cinco). In the LC method, the separation and quantitation of the 2 drugs was achieved on a Zorbax C8 column (5 microm, 150 x 4.6 mm id) using a mobile phase composed of methanol-phosphate buffer, pH 2.5 (66 + 34, v/v), at a flow rate of 1 mL/min and ultraviolet detection at 300 and 327 nm for Ace and Cinco, respectively. The method showed linearity over concentration ranges of 20-200 and 45-685 microg/mL, respectively. In the TLC-densitometry method, a mobile phase composed of methanol-tetrahydrofuran-acetic acid (45 + 5 + 0.5, v/v/v) was used for the separation of the 2 drugs. The linearity range was 0.5-4 and 2-9 microg/spot, respectively. In addition, stability indicating TLC-densitometry method has been developed for determination of cefuroxime sodium in the presence of 5-70% of its known hydrolytic degradation products. The mobile phase butanol-methanol-tetrahydrofuran-concentrated ammonium hydroxide (50 + 50 + 50' + 5, v/v/v/v) was used. The concentration range was 2-10 microg/spot. The optimized methods proved to be specific and accurate for the analysis of the cited drugs in laboratory-prepared mixtures and dosage forms. The obtained results agreed statistically with those obtained by the reference methods.

Rapid determination of cinchocaine in skin by high-performance liquid chromatography

A simple, rapid, accurate, precise and specific analytical method has been developed, validated and applied for determination of cinchocaine in guinea pig and albino rabbit dorsal skins, after in vivo application of cinchocaine formulations. Extraction was performed using a solvent mixture of ethanol and 0.1 M hydrochloric acid (90:10; v/v). Samples were chromatographed on Spheri-5, RP(18) column with a particle size of 5 microm and 220 mm x 4.6 mm i.d. The mobile phase was a mixture of acetonitrile and triethylamine phosphate buffer (pH 2.8; 0.04 M) (60:40, v/v). UV detection was carried out at 247 nm and the run time was 6 min with typical retention time of cinchocaine of 3.63 +/- 0.02 min. Specificity was demonstrated, showing that the cinchocaine peak was free of interference from skin endogenous components. The detector response was found to be linear in the concentration range 0.96-56.00 microg/mL with a coefficient of correlation r = 0.99996. The relative standard deviations of within- and between-day analyses were all below 5%. The drug extraction procedure was validated. Satisfactory recoveries with relative standard deviation values below 5% were obtained, indicating efficient quantitative reproducible extraction procedure.

Cinchocaine hydrochloride determination by atomic absorption spectrometry and spectrophotometry

Two sensitive spectrophotometric and atomic absorption spectrometric procedures have been developed for determination of cinchocaine hydrochloride (Cin.Cl) in pure form and in pharmaceutical formulation. The spectrophotometric method was based on formation of an insoluble colored ion-associate between the cited drug and tetrathiocyanatocobaltate (CoTC) or hexathiocyanatochromate (CrTC) which dissolved and extracted in an organic solvent. The optimal experimental conditions for quantitative extraction such as pH, concentration of the reagents and solvent were studied. Toluene and iso-butyl alcohol proved to be the most suitable solvents for quantitative extraction of Cin-CoTC and Cin-CrTC ion-associates with maximum absorbance at 620 and 555 nm, respectively. The optimum concentration ranges, molar absorptivities, Ringbom ranges and Sandell sensitivities were also evaluated. The atomic absorption spectrometric method is based on measuring of the excess cobalt or chromium in the aqueous solution, after precipitation of the drug, at 240.7 and 357.9 nm, respectively. Linear application ranges, characteristic masses and detection limits were 57.99-361.9, 50.40 and 4.22 microg ml(-1) of Cin.Cl, in case of CoTC, while 37.99-379.9, 18.94 and 0.81 microg ml(-1) in case of CrTC.

Sensitive and selective determination of tetracaine and its metabolite in human samples by gas chromatography-mass spectrometry

A sensitive and reliable method was developed for the determination of tetracaine and its metabolite, p-butylaminobenzoic acid, in human samples. Tetracaine and the metabolite, effectively extracted using a liquid-liquid extraction procedure from 0.5 g of sample, were analyzed by gas chromatography-mass spectrometry. Tetracaine was analyzed without derivatization, and the metabolite was analyzed after tert-butylolimethylsilyl derivatization. Dibucaine and p-dimethylaminobenzoic acid were used as internal standards for tetracaine and the metabolite, respectively. The calibration curve for each compound was linear in the concentration range from 10 to 1,000 ng/0.5 g, and the lower limits of detection were 10 ng/g for tetracaine and 0.6 ng/g for the metabolite in whole blood and tissues. The accuracy and precision of the method were evaluated in whole blood and brain at the concentrations of 50 ng/0.5 g and 500 ng/0.5 g for tetracaine and 10 ng/0.5 g and 100 ng/0.5 g for the metabolite. The coefficients of variation ranged from 0.8 to 3.0% for tetracaine and 2.4 to 9.8% for the metabolite. We used this method to determine tetracaine and its metabolite in human whole blood and tissues of an autopsied patient who died during spinal anesthesia induced by tetracaine.

First derivative spectrophotometric and high-performance liquid chromatographic determination of cinchocaine hydrochloride in presence of its acid degradation product

Two methods are presented for the determination of cinchocaine HCl in presence of its acid-induced degradation product using first (1D) derivative spectrophotometry and high-performance liquid chromatography. Cinchocaine HCl was determined by measurement of its first derivative amplitude at the zero crossing point of 2-hydroxyquinoline-4-carboxylic acid diethylaminoethylamide as its acid degradation product (at 333.5 nm). The HPLC method depends upon using a mu Bondapak C18 column at ambient temperature with a mobile phase consisting of acetonitrile--0.01 M sodium acetate trihydrate (45:55, v/v) containing 0.06% (w/v) heptane sulphonic acid sodium salt and adjusted to apparent pH 4.5 with acetic acid at a flow rate 2 ml min-1. Quantitation was achieved with UV detection at 254 nm based on peak area. The HPLC method was applied for simultaneous determination of cinchocaine HCl, methylparaben and propylparaben. The two proposed methods were successfully applied to the determination of the cinchocaine HCl in laboratory-prepared mixtures in the presence of its acid degradation product and in cream. Moreover, the proposed methods were utilized to investigate the kinetics of the acid degradation process at different temperatures and the apparent pseudo first-order rate constant, half-life and activation energy calculated.

Chromatography of crotamiton and its application to the determination of active ingredients in ointments

Crotamiton, which is a mixture of cis and trans isomers, was investigated by several separation techniques. One of the HPLC modes, in which crotamiton eluted as a single peak, was selected for the determination of five active ingredients (crotamiton, prednisolone, glycyrrhetinic acid, dibucaine and chlorhexidine hydrochloride) in an ointment. The simultaneous determination was performed using isocratic reversed-phase mode within 20 min by employing an octyl (C8) column and a mobile phase containing sodium dodecyl sulfate (SDS) and 2-propanol. The method was successfully applied to quality control and stability testing of the ointment.

Depth profiling of dibucaine in sarcoplasmic reticulum vesicles by fluorescence quenching

The location of molecules of the local anesthetic dibucaine in sarcoplasmic reticulum vesicles (SRV) was determined using the quenching of its intrinsic fluorescence by iodide and by nitroxide-labeled stearic acids (SASL) with the nitroxide group at different positions of the fatty acyl chain. The molar ratios of dibucaine to Ca(2+)-ATPase in the samples were less than 1. The acid-base titration of membrane bound dibucaine revealed a pK of 9.1, showing a negligible shift upon binding. The quenching data were obtained at pH 6.8 and are therefore related to protonated dibucaine. Quenching by iodide showed SRV-bound dibucaine to be more protected from collisions with iodide anion than dibucaine in buffer or even in neutral micelles. This shows the influence of negatively charged lipids in keeping iodide away from the ionic diffuse layer of the membrane surface where the dibucaine tertiary amine might be located. Analysis of the SASL quenching data indicates that dibucaine molecules are at a shallow position in the membrane bilayer. Their average depth was found to be at most that of the fourth carbon atom of the fatty acyl chain. The results do not exclude a preferential site for dibucaine in Ca(2+)-ATPase, but if there is such site it must be located at the protein/lipid interface.

Interactions between local anesthetic dibucaine and pig erythrocyte membranes as studied by proton and phosphorus-31 nuclear magnetic resonance spectroscopy

The interactions between amine local anesthetic dibucaine and pig erythrocyte membranes have been studied by proton and phosphorus-31 nuclear magnetic resonance (1H- and 31P-NMR) spectroscopy. It was found that dibucaine, bound to the membranes, increases the mobility of the hydrophobic acyl chains of the phospholipids, but that it decreases the mobility and/or changes the structure of the polar headgroups. The interactions with peripheral membrane proteins, i.e., spectrin and actin, were found to be weak. These observations indicate that the dibucaine locates across the polar and hydrophobic areas of the lipid phase of the membranes by both electrostatic and hydrophobic interactions. It is assumed that the changes in the mobility and/or the conformation of the phospholipids residing around the Na channel protein are essential in causing anesthesia.

Use of ion-exchange membranes to measure transfer free energies of charged local anesthetics: correlation to anesthetic potency

Ion-selective electrodes, sensitive to local anesthetic cations, were prepared with carboxylated poly(vinyl chloride) (PVC) membranes. Three plasticizers with varying degrees of polarity were used to adjust the hydrophobicity of the membrane. The affinity of the drug to the ion-exchange membrane was measured by the electromotive force of the cation-selective electrodes. The difference in the transfer free energies of the anesthetics for the membrane was estimated in reference to dibucaine. The values correlated to their clinical potencies. By comparing drugs with similar structures, the transfer free energy per methylene moiety linked to the hydrophilic domain was found to be -1.7 kJ.mol-1, and that of Cl linked to the hydrophobic domain was -3.1 kJ.mol-1. Interferences from Na+ and K+ were estimated as the selectivity coefficients against dibucaine. The values were 2.6 x 10(-5) for Na+ and 1.2 x 10(-4) for K+. The ion-exchange membrane appears to mimic the surface properties of cell membranes. These cation-selective electrodes have potential applicability in measuring charged local anesthetic concentrations (activities) in biological materials under limited conditions.

Self-association of local anaesthetic drugs in aqueous solution

The aggregation characteristics of a series of local anaesthetic drugs in water and electrolyte solution have been examined using total intensity light scattering, photon correlation spectroscopy and vapour pressure osmometry. The association of cinchocaine hydrochloride was micellar. An appreciable increase in the effective diffusion coefficient as solutions of cinchocaine were diluted close to the critical micelle concentration was observed and has been discussed. The association of amethocaine hydrochloride could be described using a co-operative stepwise association model. No association could be detected in water or 0.1 mol dm-3 electrolyte for butacaine hemisulphate and the hydrochlorides of procaine, proparacaine, mepivacaine, lignocaine, bupivacaine and prilocaine at drug concentrations of less than 0.2 mol dm-3.

Serum atypical pseudocholinesterase and leprosy

The frequency of the serum atypical pseudochloinesterase variant was significantly higher (p less than 0.005) in a group of 115 lepromatous leprosy patients than in a comparison group of 133 healthy individuals. This finding corroborates the results obtained in the group of patients from India, and supports the contention that the serum atypical pseudocholinesterase is one of the possible genetic factors involved in susceptibility to leprosy.

Release characteristics of dibucaine dispersed in konjac gels

A possible use of konjac gel for sustained release of drugs was examined in a monolithic system containing dibucaine. Dibucaine was dispersed in the gel which was prepared by gelation of the konjac flour in a borax solution at 60 degrees. The cumulative amount of the drug released plotted against the square root of time was linear in the monolithic system. This relationship was in agreement with that expected from the theoretical equation for planar configuration. The mechanism of the release of the drug from the gel may be considered to be leaching of the drug by the permeating fluid. The release profile from dried konjac gel was similar to that from undried gel, but that from unwarmed gel showed a deviation from linearity although sustained release was similarly obtained.

[Thin-layer chromatography of active compounds from ointments and suppositories followed by direct quantitative analysis by remission (author's transl)]

The paper describes a method for simultaneous thin-layer chromatographic separation of hydrocortisone, hydrocortisone acetate or hydrocortisone caproate alongside dibucaine hydrochloride, hexachlorophene and clemizole undecylate as well as clemizole hexachlorophenate in ointments and suppositories. Development of thin-layer chromatograms is carried out on silica gel 60 F-254 pre-coated plates. All four active ingredients can be separated on one silica gel plate using one solvent system and determined directly by the remission method using a densitometer. Hydrocortisone and its two esters are measured at 248 nm, dibucaine hydrochloride at 325 nm, hexachlorophene at 300 nm, and clemizole undecylate as well as clemizole hexachlorophenate at 275 nm. Evaluation of thin-layer chromatograms takes place on-line from a linear calibration curve using an IBM 1800 computer. The described method is very suitable for analyses of these active ingredients in drug forms, such as ointments or suppositories and is reproducible with coefficients of variation of 1.29-3.56%.