Liquid extraction and HPLC-DAD assay of hydrochlorothiazide from plasma for a bioequivalence study at the lowest therapeutic dose

The main parameters considered in optimizing the liquid extraction and quantitative assay were the yield, precision, limit of quantification, time required for extraction and concentration, and quantity of solvent. The influence on these parameters of the following factors was examined: nature of the extracting solvent, quantity of solvent, co-extraction solvent, and duration of stirring. Instead of equilibrium parameters of the involved thermodynamic system, a kinetic approach was preferred in terms of the effective partition 'constant', which is not really constant but a function of time and extraction conditions. The final selected method, considered to be rapid and simple, was applied to determine the pharmacokinetics of hydrochlorotiazide (HCT) after administration of Capozide (Bristol-Myers Squibb) tablets containing 50 mg Captopril and 25 mg HCT, to 4 healthy volunteers. The results obtained were in accordance with the pharmacokinetic parameters of HCT reported in the literature.

The reliability of medication inventory methods compared to serum levels of cardiovascular drugs in the elderly

Medication inventory is more reliable than self-report in assessing prescription drug use in elderly populations. It is not known how strongly medication inventory reflects actual medication use as measured by serum drug levels. In the Cardiovascular Health Study, medication data were collected annually by study interviewers from medication containers brought to the clinic visit. At the fourth clinic visit, venipuncture was performed under 12-hour fasting conditions. Participants were told to take medications as usual. Based on medication inventory results, we randomly selected 55 users and 55 non-users of four cardiovascular drugs: aspirin, propranolol, hydrochlorothiazide, and digoxin. All 110 blood samples for each of the four drugs were analyzed; cut points were based on detectable levels given laboratory limitations. Kappa statistics (K) tested degree of agreement between medication inventory findings and serum detection. Assays were completed on 400 samples (91%). Agreement for aspirin (n=102) was poor: K=0.16 (95% CI: 0.0-0.32). Agreement for propranolol (n = 98) was fair: K=0.43 (95% CI: 0.27-0.59). Agreement for hydrochlorothiazide (n=100) was good: K=0.62 (95% CI: 0.53-0.91). Agreement for digoxin (n=100) was excellent: K=0.94 (95% CI: 0.74-1.0). For four all drugs, lack of agreement was confined primarily to participants who reported use but did not have detectable levels. Excluding aspirin users, only one non-user (0.7%) had drug detected in serum. The medication inventory is a reasonably sensitive and a fairly reliable method for ascertaining non-aspirin cardiovascular drug use in the elderly even though this method may overestimate use as assessed by serum level.

New sensitive method for the determination of hydrochlorothiazide in human serum by high-performance liquid chromatography with electrochemical detection

A HPLC method with a very sensitive electrochemical detection has been developed for determining the diuretic agent hydrochlorothiazide (HCT) in serum of volunteers to whom a single dose of the fixed combination of 12.5 mg HCT and 25 mg triamterene was administered. In the present method samples (0.2 ml serum, pH 7) were purified by extraction of HCT into 5 ml tert.-butyl-methyl ether. The separated organic phase was spiked with p-aminobenzoic acid (PABA) standard. The separation was performed on a reversed-phase C18 column using phosphate buffer-acetonitrile (90:10). A coulometric cell was used to measure HCT and an ultraviolet detector for PABA. The limit of quantitation for serum samples of only 200 microliters was 5 ng/ml (i.e. 60 pg HCT/injection) with a good reproducibility (1-8%). Short retention times were found: 1.2 min for PABA and 5.8 min for HCT.

Effect of hydrochlorothiazide on the pharmacokinetics of enalapril in hypertensive patients with varying renal function

An open, randomised, cross-over study was performed to investigate the pharmacokinetics of enalaprilat, administered as 20 mg enalapril both as monotherapy and in combination with hydrochlorothiazide (HCTZ 12.5 mg). Three groups of 6 hypertensive patients were enrolled [untreated diastolic blood pressure (DBP) 90-115 mm Hg]; normal renal function [glomerular filtration rate (GFR) > 81 ml min-1 1.73 m-2], mild renal impairment (GFR 51-80 ml min-1 1.73 m-2), and moderate renal impairment (GFR 31-50 ml min-1 1.73 m-2). The pharmacokinetics of enalaprilat and enalaprilat plus HCTZ correlated predictably with renal impairment with increased plasma concentrations and decreased urinary elimination at lower values of GFR. The coadministration of HCTZ had no significant effect on the pharmacokinetics of enalaprilat in any group. We conclude that although the pharmacokinetics of both enalaprilat and HCTZ are related to renal function, HCTZ has no significant effect on the pharmacokinetics of enalaprilat and that dosage adjustment for both regimens should be based on renal function.

[The pharmacokinetics of different drug forms of nifedipine when used singly and in a course as monotherapy and in combination with Cordanum and triampur preparations in patients with arterial hypertension]

Pharmacokinetics of three drugs derived from nifedipine: corinfar, corinfar retard, and SL adalate in the cases of a single and course administration in patients with arterial hypertension and the effect of cordanum and triampur on pharmacokinetics of corinfar retard in combined repeated administration have been studied. The studies were carried out in 6 groups of patients with arterial Hypertension, each group included 10 patients. Nifedipine concentration in blood plasma was determined using a special HPLC procedure within 24 h after administration of the drugs at a dose 20 mg. A pharmacokinetic characteristics of new drug adalate SL with two-step liberation of nifedipine. A possibility of autoinhibition was noted for corinfar and adalate SL in course therapy. A conclusion was made that cordanum and triampur did not affect the pharmacokinetics of corinfar retard.

Natriuretic and diuretic effects of felodipine and hydrochlorothiazide after single and repeated doses

The effects of the calcium antagonist, felodipine, and hydrochlorothiazide (HCTZ) on natriuresis/diuresis and blood pressure were evaluated in 12 healthy subjects. The investigation was designed as a double-blind, three-way, randomised, crossover study, and all comparisons were performed against placebo. Urine volume, urine sodium excretion, heart rate and blood pressure were measured after a single dose of felodipine 10 mg, HCTZ 12.5 mg or placebo as well as during steady-state conditions (6 days of treatment with felodipine 10 mg b.i.d., HCTZ 12.5 mg b.i.d. or placebo). A significant increase in natriuresis was seen in the first 4 h after a single dose of felodipine and HCTZ, and the effect of felodipine was approximately 40% that of HCTZ. When the entire 24-h period after a single dose was studied, there was a significant increase in natriuresis after HCTZ, but not after felodipine, compared with placebo. A significant increase in diuresis was found in the first 4 h after a single dose of HCTZ, but not after felodipine, compared with placebo. Under steady-state conditions, there were no statistically significant differences between felodipine and placebo or HCTZ and placebo when the 24-h period, as a whole was considered. Potassium excretion was not affected by any of the drugs. Felodipine caused a significant decrease in diastolic blood pressure in this study. This was not the case for HCTZ or placebo.

Fully automated methods for the determination of hydrochlorothiazide in human plasma and urine

LC assays utilizing fully automated sample preparation procedures on Zymark PyTechnology Robot and BenchMate Workstation for the quantification of hydrochlorothiazide (HCTZ) in human plasma and urine have been developed. After aliquoting plasma and urine samples, and adding internal standard (IS) manually, the robot executed buffer and organic solvent addition, liquid-liquid extraction, solvent evaporation and on-line LC injection steps for plasma samples, whereas, BenchMate performed buffer and organic solvent addition, liquid-liquid and solid-phase extractions, and on-line LC injection steps for urine samples. Chromatographic separations were carried out on Beckman Octyl Ultrasphere column using the mobile phase composed of 12% (v/v) acetonitrile and 88% of either an ion-pairing reagent (plasma) or 0.1% trifluoroacetic acid (urine). The eluent from the column was monitored with UV detector (271 nm). Peak heights for HCTZ and IS were automatically processed using a PE-Nelson ACCESS*CHROM laboratory automation system. The assays have been validated in the concentration range of 2-100 ng ml-1 in plasma and 0.1-20 micrograms ml-1 in urine. Both plasma and urine assays have the sensitivity and specificity necessary to determine plasma and urine concentrations of HCTZ from low dose (6.25/12.5 mg) administration of HCTZ to human subjects in the presence or absence of losartan.

[A pharmacokinetic study of korinfar-retard in monotherapy and in combination with cordanum and triampur in patients with arterial hypertension]

The long-acting corinfar formulation, corinfar-retard tablets, 20 mg (AWD, Germany), was studied for pharmacokinetics in single and course use in 40 patients with arterial hypertension, as well as for its effects of cordanum and triampur. Patients' plasma corinfar was measured by high performance liquid chromatography. There were no changes in the pharmacokinetics of the agent when it was used in its course use. Cordanum and triampur was demonstrated to have no effects on the pharmacokinetics of corinfar during their application.

Carbonic anhydrase-immobilized precolumn for selective on-line sample pretreatment in high-performance liquid chromatographic determination of certain sulphonamide drugs

Carbonic anhydrase (CA)-immobilized aminopropyl silica precolumn was developed for direct injection determination of certain sulphonamide drugs in biological fluids by column-switching (CS) high-performance liquid chromatography. Under the optimized conditions, only the sulphonamide drugs with an unsubstituted sulphonamide group were retained on the CA precolumn and separated on a reversed-phase analytical column. Of these, the retention of hydrochlorothiazide (HCT), chlorothiazide, acetazolamide, furosemide (FS) and chlorthalidone was almost quantitative. The peak area of HCT was proportional to the concentration in the range of 1-100 nmol/mL with relative standard deviations of 3.7% (5 nmol/mL) and 0.7% (100 nmol/mL). This CS system was applied to urine and plasma samples spiked with HCT and FS. Endogenous components of these were effectively removed, and HCT and FS were selectively retained on the CA precolumn. Almost quantitative recoveries and reproducibility were obtained.

Contrasting effects of pyrazinoylguanidine and hydrochlorothiazide in patients with renal insufficiency

A single blind crossover study with washout phases showed that pyrazinoylguanidine (PZG) reduced elevated serum concentrations of urea, triglycerides, and cholesterol in patients with renal insufficiency. Pyrazinoylguanidine was saluretic, without affecting serum potassium or glucose concentrations. The onset of PZG's antihypertensive effect occurred within 4 hours. In contrast, hydrochlorothiazide (HCTZ) increased serum concentrations of urea, triglycerides, and glucose, without affecting cholesterol.

Simple determination of hydrochlorothiazide in human plasma and urine by high performance liquid chromatography

The diuretic drug hydrochlorothiazide (HCT) is used mainly for treatment of mild to moderate hypertension and is usually administered with other drugs. An assay for the determination of HCT in human plasma and urine by high performance liquid chromatography (HPLC) has been developed. Samples were purified by solvent extraction and analysed by reversed phase HPLC with ultraviolet detection, using hydroflumethiazide as the internal standard; plasma was eluted using gradient elution and urine was analysed isocratically. The method is simple to perform, is sensitive (detection limit 0.01 micrograms/mL in plasma and 0.2 micrograms/mL for urine); it showed good reproducibility (3-8%). A great number of drugs did not interfere with the assay and the method was used for pharmacokinetic studies in healthy subjects, but samples from patients can also be analysed with high selectivity.

The influence of gastrointestinal transit on drug absorption in healthy volunteers

1. The effect of variability of gastric emptying and oro-caecal transit on the absorption of a multicomponent solution of frusemide, atenolol, hydrochlorthiazide and salicylic acid has been studied in six healthy subjects. Each subject was studied on five separate occasions: three times under basal conditions, once following metoclopramide and once following codeine pretreatment in an attempt to speed and slow transit respectively. 2. Inter-subject variability of gastric emptying, oro-caecal transit and the rate and extent of drug absorption was considerable. 3. The absorption of salicylic acid appeared rate-limited by gastric emptying but the rate and extent of frusemide, atenolol and hydrochlorthiazide absorption were unrelated to measures of gastric emptying or oro-caecal transit. 4. Codeine phosphate caused a two-fold delay in oro-caecal transit but did not influence gastric emptying while metoclopramide had no significant effect on either function. 5. Metoclopramide and codeine had no significant effect on the rate or extent of absorption of any of the study drugs. 6. Within the limits of this experiment, oro-caecal transit time did not appear to be an important determinant of frusemide, atenolol, hydrochlorothiazide or salicylic acid absorption. Other factors must account for the observed variability in drug absorption.

Effects of a non-absorbable osmotic load on drug absorption in healthy volunteers

1. We have studied the effects of a non-absorbable osmotic load on the absorption of a multicomponent solution of frusemide, atenolol, hydrochlorothiazide and salicylic acid in six healthy volunteers. 2. Each subject was studied on up to four separate occasions. The drugs were administered in one of four solutions: a) a mannitol/electrolyte solution, b) a double-strength mannitol/electrolyte solution, c) a glucose/electrolyte solution and d) water. Lactulose or sulphasalazine were added as oro-caecal transit markers. Lactulose was included in the mannitol- and glucose-based solutions, adding a further non-absorbable osmotic load, and sulphasalazine was added to the water, adding little osmotic load. 3. The absorption of atenolol and hydrochlorothiazide was two- to three-times less from all lactulose-containing solutions than from the sulphasalazine-containing solution. The absorption of frusemide and salicylic acid was similar from all four solutions. 4. The largest non-absorbable osmotic load impaired the absorption of atenolol and hydrochlorothiazide most and the incorporation of glucose only partly restored absorption. 5. These results suggest that transmucosal water movement is an important determinant of atenolol and hydrochlorothiazide absorption but is less relevant for the absorption of frusemide and salicylic acid. Furthermore, these data demonstrate a previously unrecognised interaction between a commonly prescribed laxative--lactulose, and atenolol and hydrochlorothiazide.

Erythrocytes as a total barrier for renal excretion of hydrochlorothiazide: slow influx and efflux across erythrocyte membranes

The potential barrier effect of erythrocytes (RBC) on renal excretion (mainly by tubular secretion) of hydrochlorothiazide (HCTZ) was evaluated in nine anesthetized rats during steady-state iv infusion. Drug concentrations in plasma and blood from the carotid artery and renal vein were assayed by a simple modified HPLC method. Renal extraction ratios were concentration-independent with a mean of 0.17 +/- 0.05 (SD). The renal excretion was found to occur primarily from the drug in plasma; the mean net fractional removal from plasma was 0.57 +/- 0.12, while that from RBC was less than 0.008 +/- 0.041. The virtual total unavailability of HCTZ from RBC (containing approximately 70% of drug in arterial blood) for renal excretion is attributed to relatively slow efflux of drug from RBC to plasma during each passage through the kidney compared with the blood transit time (in seconds). Preliminary in vitro influx and efflux kinetics of HCTZ across RBC membranes were studied using rat and human blood. The flux data could be adequately described by a linear, reversible, closed two-component system model, and the mean equilibration half-times (ET1/2) in rat and human blood were 10.9 and 20.5 min, respectively. The mean residence time of drug in blood circulation of rats was estimated to be 8.32 +/- 1.06 min, which is shorter than the ET1/2. This is consistent with data indicating that distribution equilibrium of HCTZ in arterial blood might not be reached in vivo even at steady state. Other implications of slow transport kinetics of drugs across RBC membranes are discussed.

Large differences in the biological half-life and volume of distribution of hydrochlorothiazide in normal subjects from eleven studies. Correlation with their last blood sampling times

In spite of more than three decades of wide use of hydrochlorothiazide as a diuretic, its mean biological half-life (t1/2) and apparent volume of distribution (Vdarea) in normal subjects were found to vary greatly among 11 studies reported between 1976 and 1986. For example, the mean t1/2 values ranged from 3.2 to 13.1 h and Vdarea values from 1.53 to 4.19 l/kg. Furthermore, a t1/2 of only 2.5 h and a Vdarea of only 0.83 l/kg were cited in a recent textbook. The present analyses show a positive correlation between the length of the last blood sampling time (tlast) employed and the t1/2 or Vdarea. The smaller t1/2 and Vdarea values reported were attributed to the insufficient length of time used in blood sampling for a drug exhibiting polyexponential disposition function. The kinetic and dynamic significance of the findings were briefly described.

Column-switching high-performance liquid chromatographic (HPLC) determination of hydrochlorothiazide in rat, dog, and human plasma

A fully automated HPLC assay for hydrochlorothiazide in plasma has been developed using a column-switching technique. The method involves direct injection of plasma to the extraction column for sample cleanup followed by switching onto the analytical column. Good precision, accuracy, and linearity were obtained over a range of 25 to 2000 ng/ml in rat, dog, and human plasma. The column-switching method has also been validated by comparison with a conventional HPLC method requiring a cumbersome plasma extraction procedure. Since the method is simple, rapid, and reproducible, it is useful for determination of hydrochlorothiazide levels in animal and human plasma.

Binding of 2-amino-4-chloro-m-benzenedisulfonamide as a metabolite of hydrochlorothiazide to erythrocytes

2-Amino-4-chloro-m-benzenedisulfonamide (ACBS) is a metabolite of hydrochlorothiazide. We reported that the ACBS concentration in erythrocytes was higher than in plasma in a patient. Therefore the binding of ACBS to rabbit erythrocyte was studied. The Scatchard plot showed the nonlinear plot and the horizontal asymptote. Curvature in this plot indicated the existence of 2 classes of binding. One class was at a specific site, probably at carbonic anhydrase. Chromatographic data seemed to support the possibility.

Binding of hydrochlorothiazide to erythrocytes

Hydrochlorothiazide (HCT) was administered orally to healthy volunteers and intravenously to rabbits. HCT concentrations in plasma (Cp) and erythrocytes (Ce) were determined by a high-performance liquid chromatographic method. Ce was about 9-fold that of Cp 24 h after the administration to volunteers, and 8-fold 6 h after the administration to rabbits. From the results of the in vitro binding study which was done with rabbit erythrocytes, at least the presence of three kinds of binding site for HCT was expected. The first binding site was characterized by extremely high affinity and very low capacity, and was unaffected by acetazolamide, known as a carbonic anhydrase inhibitor. The second one was characterized by medium affinity and medium capacity, and disappeared under the presence of acetazolamide and may be due to the carbonic anhydrase of erythrocytes. The third one was characterized by low affinity, but its binding capacity was extremely high and apparently unsaturable in the HCT concentration range studied (0.5-100 micrograms/ml = 1.68-336 microM). The binding of HCT to erythrocytes seems to be dominated by the second binding site in the therapeutic range (under 1 microgram/ml of plasma).