Electrochemical study of hydrochlorothiazide and its determination in urine and tablets

A voltammetric study of hydrochlorothiazide (HCTZ) at glassy carbon electrode was carried out. The drug in Britton-Robinson buffer (pH 3.3) is oxidized at +1040mV, giving rise to a well-defined peak. Cyclic voltammetric study indicates that the oxidation process is irreversible and diffusion-controlled. A sensitive, simple and time-saving differential pulse anodic voltammetric procedure has been developed. The procedure has been applied for the drug determination in human urine with no prior extraction and in commercial tablets. The proposed method has been validated. The limit of detection for the standard solution was 5.0ngml(-1) and for the drug in urine was 14.0ngml(-1). The results obtained from the analysis of commercial tablets were compared statistically with those obtained from the USP 26 high-performance liquid chromatographic (HPLC) method.

Chemometric determination of amiloride hydrochloride, atenolol, hydrochlorothiazide and timolol maleate in synthetic mixtures and pharmaceutical formulations

Different chemometric methods such as classical least squares (CLS), principal components regression (PCR) and partial least squares with one dependent variable (PLS-1) applied on UV spectral data (0 D) and on their first derivatives (1 D) were evaluated for the simultaneous quantification of samples containing mixtures of amiloride hydrochloride, atenolol, hydrochlorothiazide and timolol maleate. Their performances were compared by means of ANOVA tests, which evidenced that 0 D-PCR, 0D-PLS-1, 1D-PCR, 1D-PLS-1, were reproducible and gave statistically similar results, while 0 D-CLS and 1D-CLS displayed higher variances than the former and failed to comply with the Levene's variance homogeneity test at different stages of the method comparison and validation process. The four statistically equivalent procedures were successfully applied to the analysis of synthetic samples with two to four analytes and to commercial tablet preparations containing amiloride hydrochloride and hydrochlorothiazide alone or in association with atenolol or timolol maleate.

Simultaneous determination of moexipril hydrochloride and hydrochlorothiazide in tablets by derivative spectrophotometric and high-performance liquid chromatographic methods

Two new simple and selective assay methods have been presented for the binary mixtures of moexipril hydrochloride (MOEX) and hydrochlorothiazide (HCTZ) in pharmaceutical formulations. The first method depends on second-derivative ultraviolet spectrophotometry with zero-crossing measurements at 215 and 234 nm for MOEX and HCTZ, respectively. The assay was linear over the concentration ranges 1.0-11.0 microg ml(-1) for MOEX and 0.5-9.0 microg ml(-1) for HCTZ. The determination limits for MOEX and HCTZ were found to be 1.0 and 0.5 microg ml(-1), respectively; while the detection limits were 0.2 microg ml(-1) for MOEX and 0.1 microg ml(-1) for HCTZ. The second method was based on isocratic reversed-phase liquid chromatography by using a mobile phase acetonitrile-20 mM phosphate buffer (pH 4.0) (50:50, v/v). Lisinopril was used as an internal standard (IS) and the substances were detected at 212 nm. The linearity range for both drugs was 0.5-12.0 microg ml(-1). The determination and detection limits were found to be 0.100 and 0.010 microg ml(-1) for MOEX and 0.025 and 0.005 microg ml(-1) for HCTZ, respectively. The proposed methods were successfully applied to the determination of these drugs in synthetic mixtures and commercially available tablets with a high percentage recovery, good accuracy and precision.

Multiple sources of sodium starch glycolate, NF: evaluation of functional equivalence and development of standard performance tests

Sodium starch glycolate is a commonly used super-disintegrant employed to promote rapid disintegration and dissolution of IR solid dosage forms. It is manufactured by chemical modification of starch, i.e., carboxymethylation to enhance hydrophilicity and cross-linking to reduce solubility. It has been reported in the literature that the source of starch, particle size, amount of sodium chloride (reaction by-product), viscosity, degree of substitution and cross-linking affect the functionality of sodium starch glycolate. Compendial assays provide an accurate representation of the chemical quality of an excipient, but they are not useful in describing the physical properties associated with the excipients. Physical characterization of sodium starch glycolate, NF revealed differences in particle size, surface area, porosity, surface morphology, and viscosity between two of the three sources examined. An automated liquid uptake test (in neutral and acidic medium) demonstrated similar initial rates of uptake, however, the extent of liquid uptake differed for the disintegrant powders examined. Settling volume was also observed to be different for the disintegrant from two sources. Lowering the pH of the medium reduced the rate and extent of liquid uptake and the settling volume in all instances. The extent of liquid uptake and settling volume was observed to be higher for the smaller sieve fractions in either medium, Although differences were also observed in the axial and radial disintegration force measurements of the pure disintegrant compacts, disintegration and dissolution of a model drug (hydrochlorothiazide) from either the soluble or insoluble core did not reveal any significant differences between the multiple sources.

Determination of hydrochlorothiazide and rutin in Chinese herb medicines and human urine by capillary zone electrophoresis with amperometric detection

In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the simultaneous determination of rutin (RT) and hydrochlorothiazide (HCT) in compound Chinese herb medicines and human urine samples. The two analytes could be perfectly analyzed within 12 min and showed significant current responses at carbon electrode under the optimum conditions. It was found that the linear range of HCT was from 2.0 x 10(-6) to 1.0 x 10(-4) mol l(-1) and that of RT was from 1.0 x 10(-6) to 1.0 x 10(-4) mol l(-1). Their sensitivity was determined by linear regression and calculated as 7.02 x 10(4) and 2.17 x 10(5) nA l mol(-1), respectively, and their detection limits were 5.0 x 10(-7) and 2.0 x 10(-7) mol l(-1), respectively (S/N=3). Above results demonstrated that this method was of high sensitivity, good repeatability, high selectivity and could be used in metabolic kinetics studies of medicines. Satisfactory results were obtained when this method was used to simultaneously analyze the amounts of RT and HCT in one general compound Chinese herb medicine-Zhen Ju jiang Ya Pian and human urine samples.

Simultaneous determination of amiloride hydrochloride and hydrochlorothiazide in synthetic samples and pharmaceutical formulations by multivariate analysis of spectrophotometric data

The use of multivariate spectrophotometric calibration for the simultaneous analysis of synthetic samples and commercial tablet preparations containing hydrochlorothiazide (HCT) and amiloride hydrochloride (AMH) is reported. Partial least squares (PLS-1) analysis of electronic absorption spectral data allowed the rapid and accurate resolution of mixtures in which the analyte ratios were approximately 10:1, without the need of a previous separation step and without interference from other sample constituents. The method, validated by the analysis of synthetic mixtures of both drugs, where accuracy over the linear working range as well as inter- and intra-assay precision were determined, was used in the concentration ranges of 21.7-30.4 mg l(-1) for HCT and 1.8-3.0 mg l(-1) for AMH. The proposed method was successfully applied to the evaluation of the stability of the stock solutions of the analytes in MeOH-H(2)O and to the elaboration of drug dissolution profiles of commercial tablets, results being concordant with those furnished by the USP technique. The method was also employed for the determination of drug content in two different pharmaceutical formulations, providing results that were in excellent agreement with those obtained by HPLC.

Development and validation of a stability-indicating HPLC method for the simultaneous determination of losartan potassium, hydrochlorothiazide, and their degradation products

Losartan potassium was the first in a new class of potent angiotensin II receptor antagonists which are well-tolerated in the treatment of hypertension. Losartan potassium is the active ingredient in tablets COZAAR and is combined with diuretic co-active hydrochlorothiazide (HCTZ) in tablets HYZAAR for increased efficacy. Losartan potassium has one main impurity and two primary degradates. HCTZ has one major degradate as well as two common process impurities. Historically, separate methods have been used for the analysis of each active and their respective impurities and degradates. The ultimate goal of this work was to develop and validate a single high-performance liquid chromatography method selective for the eight main components of tablets HYZAAR. A single method was developed to afford simultaneous quantitation of actives and degradates for each of the two existing formulations. Each method is presented herein and demonstrated to be suitable for quantitation to 0.1% levels of all relevant degradates, as well as 100% levels of respective drug substances.

Spectrophotometric quantitative determination of cilazapril and hydrochlorothiazide in tablets by chemometric methods

Four chemometric methods were applied to simultaneous determination of cilazapril and hydrochlorothiazide in tablets. Classical least-square (CLS), inverse least-square (ILS), principal component regression (PCR) and partial least-squares (PLS) methods do not need any priori graphical treatment of the overlapping spectra of two drugs in a mixture. For all chemometric calibrations a concentration set of the random mixture consisting of the two drugs in 0.1 M HCI and methanol (1:1) was prepared. The absorbance data in the UV-Vis spectra were measured for the 15 wavelength points (from 222 to 276 nm) in the spectral region 210-290 nm considering the intervals of deltalambda = 4 nm. The calibration of the investigated methods involves only absorbance and concentration data matrices. The developed calibrations were tested for the synthetic mixtures consisting of two drugs and using the Maple V software the chemometric calculations were performed. The results of the methods were compared each other as well as with HPLC method and a good agreement was found.

Bioavailability of hydrochlorothiazide from isomalt-based moulded tablets

The bioavailability of hydrochlorothiazide (HCT) from moulded isomalt-based tablets was evaluated after oral administration of 50 mg HCT to healthy volunteers as an oral moulded tablet and as a lozenge, in comparison with a conventional tablet formulation (Dichlotride 50 mg). Moulded tablets had a high relative bioavailability (F(rel)) as the pharmacokinetic parameters (C(max), t(max), t(1/2), AUC(0-->24 h)) determined from HCT plasma concentration versus time profiles were not significantly different (P>0.05; two-way ANOVA) in comparison with the conventional tablet. The relative bioavailability of the moulded tablet administered as a lozenge and as an oral tablet was 106.2+/-30.9% and 89.4+/-25.9%, respectively, in relation to the conventional tablet formulation. Direct moulding of isomalt tablets proved to be a suitable technique to administer a poorly soluble drug either as a conventional tablet or as a lozenge.

Purification and identification of an impurity in bulk hydrochlorothiazide

Hydrochlorothiazide (6-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide 1,1-dioxide) (HCTZ) 1 is a widely used diuretic and anti-hypertensive. Recently, the Pharmeuropa recognized a new impurity initially thought to be an HCTZ dimer 6, which consists of the active drug (HCTZ) linked via the former beta-ring methylene to a known degradate, 5-chloro-2,4-disulfamylaniline 2. In an effort to meet a new requirement, an analytical high-pressure liquid chromatography method was developed that was selective and sensitive to the subject impurity. The impurity was concentrated and purified using a combination of solid phase extraction and reverse-phase high-pressure liquid chromatography. Subsequently, the impurity has been identified as a specific HCTZ-CH2-HCTZ isomer utilizing a variety of analytical techniques, including hydrolysis, ultraviolet spectroscopy, liquid chromatography/mass spectrometry, and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. The data resulting from the application of these analytical techniques confirm the identity of the impurity as a methylene bridged pair of HCTZ molecules; however, a total of six possible isomers 7a-f exist because of the presence of three reactive amines/sulfonamides on each HCTZ molecule. One unique molecular structure (4-[[6-chloro-3,4,-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide-1,1-dioxide]-methyl]-chloro-3-hydro-H-1,2,4-benzothiadiazine-7-sulfonamide-1,1-dioxide) 7f was identified using two-dimensional COSY, NOESY, and TOCSY 1H NMR experiments.

Spectrophotometric simultaneous determination of triamterene and hydrochlorothiazide in triamterene-H tablets by multivariate calibration methods

The multivariate calibration methods of partial least-square regression and principal component regression were applied for the simultaneous spectrophotometry determination of triamterene (TRM) and hydrochlorothiazide (HYD) in their mixtures. The parameters of the chemometric procedure were optimized, and the proposed methods were validated with synthetic samples and applied to analyze these drugs in pharmaceutical products with good accuracy and precision. The results were compared with those given by the British Pharmacopoeia (BP) method. The square of the correlation coefficients (R(2)) for predicted TRM and HYD with the proposed method in a test sample were 0.9994 and 0.9992, respectively. The relative standard deviation for commercial tablets in the proposed method and BP standard method were 0.405 and 2.142%, respectively.

Physicochemical properties of liposomes incorporating hydrochlorothiazide and chlorothiazide

In an attempt to study the effect of hydrophobic drugs on liposome properties, multilamellar liposomes (MLV) consisting of phosphatidylcholine (PC) and incorporating chlorothiazide (CT) or hydrochlorothiazide (HCT), were prepared and characterized. Liposome size, surface charge, stability (in buffer, plasma and sodium cholate) and calcium-induced aggregation were studied for drug-incorporating liposomes and empty liposomes for comparison. Results show that drug incorporation affects liposome size, z-potential and stability in presence of buffer and plasma proteins. Indeed, drug-incorporating liposomes are slightly larger and have a negative surface charge, which increases with the amount of drug incorporated in the lipid membrane. The membrane integrity of drug incorporating liposomes (in absence and presence of plasma proteins) is significantly higher when compared with that of empty liposomes (for both drugs studied). On the contrary, vesicle membrane integrity in presence of sodium cholate and calcium induced vesicle aggregation, are not affected by drug incorporation. Leakage of thiazides from liposomes was demonstrated to be induced by dilution. Low amounts of thiazides (around 10-15%) are released when lipid concentration is over 0.1 mM, while further dilution increased drug leakage exponentially. Concluding, results demonstrate that the presence of HCT or CT in liposome membranes has a significant effect on main vesicle properties, which are known to influence vesicle targeting ability. Thereby, it is very interesting to continue studies in this respect, especially with more lipophilic drugs.

A comparative study of modified starches in direct compression of a poorly water soluble drug (hydrochlorothiazide)

The direct compression properties of four modified starches in hydrochlorothiazide (HCTZ) tablets were studied. The starches were obtained locally from common plant sources and were modified through physicochemical treatment. Each modified starch was used as the only filler-binder-disintegrant in the formulation of hydrochlorothiazide tablets containing 25 mg of the drug. The tablets were produced by the direct compression technology. Sta-Rx 1500, a directly compressible starch, was used as basis for comparison. Evaluated tablet properties included weight and drug content uniformity, hardness and friability as well as disintegration time and dissolution profile. The modified starches exhibited species specificity in terms of the tablet properties. The weight, drug content and disintegration time for all batches of tablets were within acceptable limits. Proper ranking of the starches on the basis of specific tablet properties was used to highlight their differences.

Liquid chromatography-mass spectrometry and proton nuclear magnetic resonance characterization of trace level condensation products formed between lactose and the amine-containing diuretic hydrochlorothiazide

Trace levels of condensation products between lactose and the amine-containing diuretic hydrochlorothiazide are formed when a mixture of the two solids containing 30% weight water is heated at 60 degrees C for 2 weeks. The two most abundant condensation products were characterized by liquid chromatography-mass spectrometry (LC-MS) and proton nuclear magnetic resonance ((1)H NMR) spectroscopy. Under these relatively mild conditions of formation, the amine-lactose reaction products are limited to those involving the elimination of only a single molecule of water, rather than the multiple-water eliminations associated with later stages of the Maillard reaction. The spectroscopic data clearly show that the primary condensation products are cyclic N-substituted glycosylamines rather than Schiff base, 1,2-enolic forms, or Amadori rearrangement products of identical mass. In solution, the two most abundant N-substituted glycosylamines are shown to be in a kinetically slow equilibrium with each other, most likely through a mutarotation involving the intermediate formation of the acyclic Schiff base.

Dissolution tests of benazepril-HCl and hydrochlorothiazide in commercial tablets: comparison of spectroscopic and high performance liquid chromatography methods

Simple, rapid and reliable spectroscopic methods (absorbance ratio and Vierordt) were compared with HPLC for quantitative determination in dissolution tests of benazepril-HCl (BNZ) and hydrochlorothiazide (HCT) in commercial tablets. A 249 nm wavelength was chosen as the isosbestic point in the absorbance ratio method, and the absorbance ratios A236/A249 nm for BNZ and A269/A249 nm for HCT were used for calculation of regression equations. For the Vierordt method, A1(1) values (%1.1 cm) obtained at 236 and 269 nm for both substances were used for quantitative analyses of BNZ and HCT. In the HPLC method, simultaneous determination of BNZ and HCT from dissolution medium was achieved using the mobile phase containing phosphate buffer (0.01 M, pH 6.2) and acetonitrile (65:35) on a Supelcocil LC-18 (4.6 x 250, 5.6 mm) reversed phase column. Dissolution tests of commercial tablets were carried out according to USP XXII paddle method in 0.1 N HCl at 50 rpm at 37 +/- 0.5 degrees C. Comparison of the dissolution data from the HPLC and two spectroscopic methods indicated that spectroscopic and HPLC methods were in good correlation with each other. Therefore, it was concluded that both spectroscopic methods as well as HPLC can be used in routine analyses of BNZ and HCT in dissolution tests of commercial tablets.

Increased phototoxicity of hydrochlorothiazide by photodegradation

The photodegradation products of hydrochlorothiazide produced by ultraviolet (UV) radiation were investigated for their phototoxicity utilizing the photohemolysis and Candida albicans tests. Hydrochlorothiazide was irradiated for 30, 60, 90 and 120 min with a 250 W xenon arc lamp using a WG295 cut-off filter. Irradiation of hydrochlorothiazide resulted in the gradual decrease of all three absorption bands (225, 270 and 320 nm), the blue shift of the 225 nm band, and the appearance of a new band around 290 nm. Since previous results demonstrated that photosubstitution of chloride could occur, the main product of this photolysis most likely is ethoxyhydrochlorothiazide. The photohemolysis test revealed a significant increase in photohemolysis observed in the photodegradation products produced after 60, 90 and 120 min of UV irradiation. This increase in hemolysis value directly correlated with the UV-irradiation time. However, there was no significant phototoxic killing of yeast in the Candida albicans test. This suggests photodegradation products of hydrochlorothiazide may play an important role in phototoxicity by acting on the cell membrane, but not on DNA. Considering the high in vitro phototoxicity observed in bendroflumethiazide and the data presented here, substitution of chloride seems to be responsible for the increased phototoxicity of hydrochlorothiazide.

Separation of theophylline, caffeine and related drugs by normal-phase capillary electrochromatography

A capillary electrochromatography (CEC) method has been developed for the separation of theophylline, caffeine and five related drugs on a normal-phase column with UV or photodiode array detection. Several binary, ternary and quaternary mobile phase compositions are evaluated for optimal resolution and elution of these drug analytes. The importance of selecting suitable organic solvents, buffer electrolyte, pH and applied voltage is demonstrated by a systematic study. Excellent separation is achieved for the eight drugs using a ternary mobile phase composition of isopropanol/hexane/1 mM Tris (52:40:8, pH 8), with an efficiency of 63000 theoretical plates per meter at room temperature. Detection limits are typically at the low microg/mL level. The developed method is simple to use and it gives acceptable day-to-day reproducibility.

Interactions of diuretics with a neutral temperature-responsive polymer: study by capillary electroporesis and dynamic light scattering

Interactions between diuretics and a recently synthesized temperature-responsive neutral copolymer, poly(N-isopropyl acrylamide) (PNIPA) grafted with poly(ethyleneoxide) (PEO) (PNIPA-g-PEO) were investigated by capillary electrophoresis and dynamic light scattering (DLS). At ambient temperatures, the copolymer takes an open, random coil conformation, but above the lower critical solution temperature (LCST), the polymer shrinks and forms large, stable aggregates. Among the diuretics studied, hydrochlorothiazide was detected to bind to PNIPA-g-PEO.

Stability of freeze-dried tablets at different relative humidities

The purpose of the study was to evaluate the stability of two different freeze-dried tablet formulations at different relative humidities (RHs). The tablets contained 25 mg hydrochlorothiazide (HCT) as a model drug and were prepared by freeze-drying a suspension and an oil-in-water (o/w) emulsion. Formulation A was a rapidly disintegrating tablet and consisted of 80 mg of maltodextrine DE38; 8 mg of polyethyleneglycol (PEG 6000), 8 mg of xanthan gum, and 25 mg of HCT. Formulation B was a lyophilized dry emulsion tablet that consisted of 160 mg of Miglyol 812, 80 mg of maltodextrin DE38, 16 mg of methylcellulose (Methocel) A15LV, and 25 mg of HCT. Tablets were packaged in different packing materials: polyvinylchloride (PVC)/aluminum blister packs, PVC-polyvinylidenechloride (PVDC)/aluminum blister packs, closed containers with a dessicant tablet, and open containers. The tablets were stored at three relative humidities (45%, 60%, and 85% RH) and were characterized on mechanical strength, residual moisture, porosity, content uniformity, and scanning electron microscopy (SEM) during a period of 6 months. After 1 month at 60% and 85% RH, a strong increase in moisture content (from 2.7% to 6.8%) was seen for the tablets packed in the open and closed containers and for the PVC/aluminum blistered tablets. This increase was higher for formulation A compared to formulation B since B contained 160 mg of triglycerides and was more hydrophobic. This increase in water content was correlated with a decrease in mechanical strength. The tablets also showed a change in microstructure and porosity. At a moisture content of 7.2%, formulation A showed a structural "collapse" since water acts as a plasticizer for the amorphous glass, lowering the glass transition temperature Tg. This phenomenon even occurred in PVC/aluminum blister packs at 85% RH. The structural collapse was associated with a complete loss of microstructure as detected by porosimetric analysis and SEM. For the PVC-PVDC/aluminum blistered tablets, the increase in moisture content and decrease in mechanical strength at 85% RH occurred much slower, and the water uptake and strength loss were less intensive. No significant breakdown of HCT could be observed in both formulations with all of the packing materials. Packaging of freeze-dried tablets with PVC/aluminum blister packs, PVC/PVDC/aluminum blister packs, or closed containers did not offer protection against moisture uptake, mechanical strength loss, and structural collapse.

Bioadhesive delivery of hydrochlorothiazide using tacca starch/SCMC and tacca starch/Carbopols 940 and 941 admixtures

Tacca starch and its admixtures with Carbopols 940 and 941; and sodium carboxymethylcellulose (SCMC) were evaluated for bioadhesive delivery of hydrochlorothiazide into the gastrointestinal tract (GIT). The bioadhesive properties were evaluated using the adhesion of polymer-coated glass beads on the antrum region of the porcine gastrointestinal tract and Lecomte Du Nouy tensiometer. The swellings and release characteristics of the films/hydrogels of tacca starch and its admixtures were also studied. Results of the bioadhesive properties indicated that although tacca starch is a poor bioadhesive biopolymer at low concentration, the admixtures showed improved bioadhesive properties. The swelling and the release characteristics also confirmed that the admixtures could be used for bioadhesive drug delivery into the GIT.

Thin-layer chromatography-mass spectrometry using activated carbon, surface-assisted laser desorption/ionization

The analysis of compounds separated by thin-layer chromatography (TLC) by surface-assisted laser desorption ionization (SALDI) mass spectrometry has been demonstrated. The compounds are analyzed from the surface of the intact TLC plate, and the preparation of the TLC plate is rapid and robust: the gel surface is covered with 2 microns activated carbon particles, and glycerol is added. Analytes diffuse from the interior of the gel to the surface where they are adsorbed onto the activated carbon. A nitrogen laser is used to desorb analyte ions from the carbon particles in a time-of-flight mass spectrometer. A wide range of organic compounds, including peptides, can be detected, either as protonated or as cationized molecules. Interference with "matrix peaks" is limited since background TLC-SALDI mass spectra typically show only a few intense peaks at low mass. The detection limit for bradykinin from a developed plate is approximately 25 ng (calculated for S/N = 3). The mass resolution (FWHM) varied from a high of about 500 to a low of about 100. This variability was likely due to surface charging. Methods to improve both mass resolution and sensitivity of TLC-SALDI are suggested.

Spectrophotometric studies on the photostability of some thiazide diuretics in ethanolic solution

First derivative and dual-wavelength spectrophotometric methods were used in the quantum yield determination of the photochemical decomposition reactions of three thiazide diuretics (chlorothiazide, hydrochlorothiazide and trichloromethiazide) in ethanolic solution. The radiation absorbed by the compounds was measured using iron(III) oxalate actinometry based on absorption spectrophotometry. An apparatus is described in which the drugs were irradiated in quartz cuvettes cooled by water in a stand built on a magnetic stirrer. The wavelength region available to the reaction cuvette was restricted to 313 nm with chemical potassium chromate filter solutions and a Corning filter plate. Chlorothiazide proved to be more photostable than hydrochlorothiazide and trichloromethiazide in ethanol.

Effect of elevated viscosity in the upper gastrointestinal tract on drug absorption in dogs

The objectives of these studies were, first, to determine the effect of elevated luminal viscosity on the gastrointestinal absorption of four model drugs and, second, to identify the key processes influencing drug absorption under elevated viscosity conditions. Studies were conducted in vitro and in healthy female mongrel dogs under fasting conditions. In the canine model, both the rate and extent of paracetamol and hydrochlorothiazide absorption were significantly decreased by the coadministration of 15 g guar gum dissolved in 500 ml normal saline. In the case of cimetidine, the rate but not extent of absorption was decreased. Owing to the high variability in the data, no statistically based conclusion could be drawn about the effects of coadministered guar gum on the oral absorption of the poorly soluble mefenamic acid. Based on the in vitro data, it appears that substantial reductions in the dissolution rate of paracetamol, hydrochlorothiazide and cimetidine account for the effects observed in vivo. It is concluded that the effect of an elevation in the intraluminal viscosity on drug absorption is greatest for highly soluble drugs, and results from a combination of a decrease in dissolution rate and gastric emptying rate.

Identification of chlorothiazide and hydrochlorothiazide UV-A photolytic decomposition products

Methanol solutions of hydrochlorothiazide and chlorothiazide were irradiated with fluorescent UV-A lamps in order to simulate degradation under normal conditions. The degradation products were identified by comparison to synthetic standards featuring electrospray ionization mass spectroscopy, ultraviolet spectroscopy, and high performance liquid chromatography. The standards were characterized by high resolution fast atom bombardment MS and 1H NMR. The photolysis of chlorothiazide resulted in photodehalogenation products exclusively, while the irradiation of hydrochlorothiazide primarily yielded photodehalogenation products with significant yields of photodehydrogenation products and minor amounts of thermal hydrolysis products.

Near-infrared spectroscopy as a nondestructive alternative to conventional tablet hardness testing

PURPOSE

Near-infrared reflectance spectroscopy (NIRS) was used to evaluate and quantify the effect of compression force on the NIR spectra of tablets.

METHODS

Flat, white tablets with no orientation (scoring, etc.) were manufactured on a Stokes Rotary Tablet Press. NIRS was used to predict tablet hardness on the following four formulations and one placebo matrix: hydrochlorothiazide (HCTZ) 15% and 20% in a placebo matrix (microcrystalline cellulose and magnesium stearate), and chlorpheniramine maleate (CTM) 2% and 6% in a placebo matrix. Five or six levels of tablet hardness from 2 to 12 kg were used for each formulation. Laboratory hardness data was compared to NIR reflectance data using a NIRSystems Rapid Content Analyzer. Multiple linear regression and partial least squares regression techniques were used to determine the relationship between tablet hardness and NIRS spectra.

RESULTS

An increase in tablet hardness produced an upward shift (increase in absorbance) in the NIRS spectra. A series of equations was developed by calibrating tablet hardness data against NIR reflectance response for each formulation. The results of NIRS hardness prediction were at least as precise as the laboratory hardness test (SE = 0.32).

CONCLUSIONS

A NIRS method is presented which has the potential as an alternative to conventional hardness testing of tablets.

The role of intra- and extragranular microcrystalline cellulose in tablet dissolution

The objective of this study was to examine the influence of intra- and extragranular microcrystalline cellulose (MCC) on drug dissolution from tablets made by high-shear granulation. Granulations were made in a Littleford Model W-10-B (10-liter) mixer and dried in a fluid bed dryer (Niro Inc.). A Plackett-Burman screening design and 2(3) factorial design were employed to study how drug type, MCC (intra- or extra-), filler type (lactose or dicalcium phosphate), disintegrant type (sodium starch glycolate or croscarmellose sodium) and level, proportion of magnesium stearate, and impeller speed affect tablet hardness, disintegration time, and dissolution. Two model drugs were chosen based on their solubility: metoprolol tartrate (solubility > 1000 mg/ml) and hydrochlorothiazide (solubility = 1.05 mg/ml). Tablets were compressed to the same target weight (dose) and similar tablet hardness. In some cases, dissolution testing was also carried out on the loose granules. The intra-extragranular distribution of MCC was found critical to the compactibility and initial dissolution rates from these tablets. Intragranular MCC reduced drug dissolution, the effect being most marked in the case of the slightly soluble hydrochlorothiazide. For formulations containing intragranular MCC, the granulating fluid level on tablet dissolution was also important, since an increase in fluid level resulted in slower drug dissolution from both the loose granules and the tablets compressed from them. Conversely, extragranular MCC tended to increase both dissolution rates and compactibility. It may be concluded that the appropriate distribution of MCC between and within granules may optimize both dissolution and compactibility without changing overall tablet composition.

Stability of labetalol hydrochloride, metoprolol tartrate, verapamil hydrochloride, and spironolactone with hydrochlorothiazide in extemporaneously compounded oral liquids

The stability of drugs commonly prescribed for use in oral liquid dosage forms but not commercially available as such was studied. Labetalol hydrochloride 40 mg/mL, metoprolol tartrate 10 mg/mL, verapamil hydrochloride 50 mg/mL, and spironolactone 5 mg/mL plus hydrochlorothiazide 5 mg/ mL were prepared in a 1:1 mixture of Ora-Sweet and Ora-Plus (Paddock Laboratories), a 1:1 mixture of Ora-Sweet SF and Ora-Plus (Paddock Laboratories), and cherry syrup and placed in polyethylene terephthalate bottles. The sources of the drugs were tablets. Six bottles were prepared per liquid; three were stored at 5 degrees C and three at 25 degrees C, all in the dark. A sample was removed from each bottle initially and at intervals up to 60 days and analyzed for drug concentration by stability-indicating high-performance liquid chromatography. At least 91% of the initial drug concentration was retained in all the oral liquids for up to 60 days. There were no substantial changes in the appearance or odor of the liquids, or in the pH. Labetalol hydrochloride 40 mg/mL, metoprolol tartrate 10 mg/mL, verapamil hydrochloride 50 mg/mL, plus hydrochlorothiazide 5 mg/ mL in three oral liquids compounded extemporaneously from sweetened vehicles and tablets were stable for up to 60 days when stored without light at 5 and 25 degrees C.

First-derivative UV spectrophotometric and high-performance liquid chromatographic analysis of some thiazide diuretics in the presence of their photodecomposition products

Ethanolic solutions of three thiazide diuretics, chlorothiazide, hydrochlorothiazide and trichlormethiazide, were irradiated with a high-pressure mercury lamp. The products were isolated and their first-derivative UV spectra in ethanol were recorded and compared to those of the parent compounds. The determination of the parent compounds in the presence of the decomposition products was carried out at wavelengths near 220 nm using the zero-crossing technique. Three reversed-phase HPLC methods were also developed for the analysis of the parent compounds. In parallel analyses of the reaction mixtures a good correlation was achieved between these two methods in the determination of hydrochlorothiazide and trichlormethiazide while there was greater variation in the results of chlorothiazide.

Multiple tamping effects on drug dissolution from capsules filled on a dosing-disk type automatic capsule filling machine

The effects of number of tamps and tamping force on drug dissolution from capsules filled on an instrumented dosing-disk automatic capsule filling machine (Hofliger-Karg) were studied using hydrochlorothiazide as a model, low dose, poorly soluble drug. Generally, there was a trend toward slower dissolution rate with increasing numbers of tamps, the effect being most marked when insoluble dicalcium phosphate dihydrate was the filler. Higher compression forces improved drug release when anhydrous lactose was the filler, but adversely affected the dicalcium phosphate-based capsules. Inclusion of 4% croscarmellose sodium disintegrant tended to nullify the effects of number of tamps or tamping force with both fillers; however, the disintegrant also markedly enhanced drug dissolution from the dicalcium phosphate-based formulation. Hydrochlorothiazide dissolution from the latter formulation without disintegrant appeared to follow a "diffusion from insoluble matrix" model regardless of number of tamps or their intensity. Mercury intrusion pore size distribution data for some plugs suggested that for tamps of equal force (100 or 200 N), further powder consolidation after two tamps does not occur.