Influence of time intervals for cholestyramine dosing on the absorption of hydrochlorothiazide

Ten healthy adult men participated in a study to evaluate appropriate dosing schedules of cholestyramine to minimize its effect on the absorption of hydrochlorothiazide (HCTZ). A single 8 gm dose of cholestyramine 2 hours before or after HCTZ, 75 mg po, significantly decreased the amount of HCTZ excreted unchanged in the urine over 24 hours (Ae(0-24)) by 65% (P less than 0.01) and 26% (P less than 0.05), respectively, in four subjects. Six subjects randomly received three different schedules: control, single dose of cholestyramine 4 hours after HCTZ, and multiple doses of cholestyramine (-24, -12, and +4 hours) after HCTZ. There were no significant differences in HCTZ kinetics between the control group and the subjects who received a single dose of cholestyramine. Multiple doses of cholestyramine significantly altered HCTZ kinetics, including reductions in Ae(0-24) by 35% (P less than 0.02), AUC(0-infinity) by 32% (P less than 0.01), and Cmax by 31% (P less than 0.01). We conclude that the best dosing schedule for cholestyramine is 4 hours after HCTZ, but there will still be at least a 30% to 35% decrease in the absorption of HCTZ.

High-performance liquid chromatographic assay for hydrochlorothiazide in human urine

A high-performance liquid chromatographic assay was developed for the quantitative determination of hydrochlorothiazide (HCT) in human urine. Reversed-phase separation of HCT and the internal standard, trichloromethiazide (TCMT), was accomplished on a 300 X 3.9 mm mu Bondapak Phenyl column. Following solvent extraction, concentrations of HCT as low as 0.25 micrograms/ml in urine were quantified by UV detection at 280 nm. Detector response (peak-area ratio of HCT to TCMT) was linear to 50 micrograms/ml. No interferences were observed in the extracts obtained from drug-free urine nor from several antihypertensive agents which are commonly co-administered with HCT. This method has been routinely employed in bio-availability studies evaluating a variety of formulations as well as characterizing the pharmacokinetics of this drug from urinary excretion data.

The development of reliable compliance tests for antihypertensive drugs

Many tests for measuring compliance have been proposed, but in most cases compliance rates have been determined without taking into account the factors influencing the interval during which a drug can be detected by a qualitative test after having been taken by the patient. The drug half-life, often used for determining the time at which the sample is collected, is inadequate for obtaining conclusive test results. A procedure is described for the determination of urine collection intervals during which reliable information on compliance can be obtained, using oxprenolol, hydrochlorothiazide, and pindolol as examples.

Exaggerated natriuretic and calciuric responses to hydrochlorothiazide in renal hypercalciuria but not in absorptive hypercalciuria

Patients with hypercalciuria have been reported to have an exaggerated response to hydrochlorothiazide (HCTZ), implying a renal tubular defect in solute reabsorption. To determine whether this disturbance is generalized or unique to a particular pathogenetic type of hypercalciuria, we measured the increments in urinary sodium (delta Na), calcium (delta Ca), and magnesium after a 100-mg dose of oral HCTZ in 10 normal subjects and 31 patients with different types of hypercalciuric nephrolithiasis. Eleven patients with renal hypercalciuria had significantly greater delta Na (P less than 0.005) and delta Ca (P less than 0.005) than the normal subjects. Ten patients with absorptive hypercalciuria and 10 patients with fasting hypercalciuria without parathyroid stimulation had delta Na and delta Ca indistinguishable from those of normal subjects. In all groups, urinary HCTZ and basal 24-h urinary Na did not differ. The results suggest that the unique natriuretic and calciuric responses to HCTZ occur only in renal hypercalciuric patients with secondary hyperparathyroidism. The data support a renal tubular defect in renal hypercalciuric in contrast to other diagnostic categories of hypercalciuric nephrolithiasis.

Accuracy of indirect measures of medication compliance in hypertension

The purpose of this study was to identify the most accurate indirect measure of medication compliance in primary hypertension through comparison with a recently developed direct measure of the antihypertensive agent, hydrochlorothiazide. A convenience sample of 40 subjects was seen by the investigator twice in an office setting and once in their homes. Data were collected by an interview schedule, blood pressure measurement, pill counts, urine analysis, and hospital record review. Patient interview was the most sensitive and accurate measure of compliance; this measure correctly classified 85% of patients as to compliant or noncompliant.

Bioequivalence study of a new tablet formulation of triamterene and hydrochlorothiazide

A three-treatment, single-dose, crossover bioequivalence study was conducted in healthy volunteers to compare urinary drug recovery following administration of hydrochlorothiazide tablets, the currently marketed capsule formulation of triamterene and hydrochlorothiazide (Dyazide), and a new tablet preparation of these active ingredients (Maxzide). No significant differences were observed in the urinary recovery of hydrochlorothiazide after the administration of hydrochlorothiazide tablets and Maxzide tablets. However, only about one-half as much hydrochlorothiazide was recovered following the administration of Dyazide capsules. Similarly, the urinary recovery of triamterene and the sulfate ester of hydroxy-triamterene after administration of Dyazide capsules was approximately one-half the levels observed after giving the new tablet formulation. The clinical consequences of the limited bioavailability of the active ingredients of Dyazide are discussed.

Simplified detection of hydrochlorothiazide in urine by thin-layer chromatography

A new thin-layer chromatographic procedure for the detection of the antihypertensive/diuretic drug hydrochlorothiazide in human urine is described. The sensitivity of the method, 5 micrograms/mL, makes it useful to both the clinician interested in determining patient compliance and the toxicologist who must identify or confirm hydrochlorothiazide ingestion. The rapidity of analysis typically allows the screening of 25 urine samples within one hour.

Comparative bioavailability and pharmacokinetics of hydrochlorothiazide from oral tablet dosage forms, determined by plasma level and urinary excretion methods

The bioavailability and pharmacokinetics of two hydrochlorothiazide products were compared following single 50 mg oral doses to 20 healthy male volunteers. Plasma and urine were assayed for hydrochlorothiazide by a specific and sensitive HPLC method. Plasma profiles of hydrochlorothiazide were adequately described by a triexponential function. The bioavailability of hydrochlorothiazide from the two brands did not differ significantly as judged by the values of Cmax, tmax, AUC0 leads to infinity, mean residence time, variance of residence time, and urinary excretion of unchanged drug. Close similarity was observed between urinary excretion rates and concentrations of drug in plasma.

On-line direct liquid introduction interface for micro-liquid chromatography/mass spectrometry: application to drug analysis

We describe an integrated micro-liquid chromatograph/mass spectrometer (micro-LC/MS) system capable of performing routine determinations for 1--10 ng of drugs and their metabolites extracted from biological fluids. The micro-LC is constructed from conventional "high-performance" liquid-chromatographic instrumentation by using commercially available components. The mass spectrometer is operated in the chemical ionization mode. The direct liquid introduction micro-LC/MS interface can be constructed from commercially available materials. Chromatographic and mass spectral results demonstrate the ability of the micro-LC and micro-LC/MS system to separate and determine multiple components in standards of trace concentrations and in equine urinary extracts. The stability and sensitivity of this micro-LC/MS system are demonstrated through determinations of trichlormethiazide.

Pharmacokinetics of hydrochlorothiazide in fasted and nonfasted subjects: a comparison of plasma level and urinary excretion methods

The bioavailability of hydrochlorothiazide from 50-mg oral tablet doses was examined in healthy male volunteers under fasting and nonfasting conditions. Bioavailability was examined from plasma levels and urinary excretion of unchanged drug. The pharmacokinetics of hydrochlorothiazide in plasma could be described in terms of a triexponential function, and the mean drug half-lives determined from the three exponents were 1.0, 2.2, and 9.0 hr. Changing the accompanying fluid volume has no significant effect on hydrochlorothiazide absorption in fasted subjects. Plasma drug levels were significantly reduced in non-fasted individuals, compared with those in fasted individuals. A similar trend was observed in the urinary excretion of hydrochlorothiazide, but differences between treatments were not significant (p greater than 0.05). Mean 48-hr urinary recovery of hydrochlorothiazide was 70.5% of the dose in nonfasted subjects, and 73.5 and 75.0% of the dose in fasted subjects receiving the drug with 20 and 250 ml of water, respectively. The cumulative urinary excretion of hydrochlorothiazide correlated poorly (r = 0.27) with areas under plasma drug level curves, although the correlation between the means of these values for each of the three treatments was high (r = 0.996).. Close similarity was observed between urinary excretion rates of hydrochlorothiazide and the time course of drug concentrations in plasma.

High-pressure liquid chromatographic determination of chlorothiazide and hydrochlorothiazide in plasma and urine: preliminary results of clinical studies

High-pressure liquid chromatographic procedures were developed for the determination of chlorothiazide and hydrochlorothiazide in plasma and urine. The plasma assay incorporates a preextraction procedure that eliminates interference by endogenous substances. Chromatography is carried out on an octadecyl reversed-phase column. Mobile phases are 15% methanol in 0.01 M acetic acid for plasma and 4% acetonitrile in 0.01 M sodium perchlorate, adjusted to pH 4.6, for urine. At a flow rate of 2.5 ml/min, the retention times for chlorothiazide and hydrochlorothiazide are 3.5 and 4.6 min for plasma and 10.5 and 13.5 min for urine, respectively. Preliminary results of a clinical study in fasting male volunteers showed that the plasma levels and urinary excretion rate of chlorothiazide peaked at 1-2 hr following a 500-mg oral dose and subsequently declined irregularly. On the other hand, the plasma levels and urinary excretion rate of hydrochlorothiazide peaked at 2-3 hr following a 50-mg oral dose and subsequently declined in biphasic fashion. Urinary excretion rates of both chlorothiazide and hydrochlorothiazide closely resemble their concentration profiles in plasma.

Can simple clinical measurements detect patient noncompliance?

Measurement of patient compliance is essential if management of low compliance is to be performed efficiently. We assessed the value of several easily obtained clinical assessments compared to quantitative pill counts among 134 newly treated hypertensive male steelworkers during the first 6 months of their treatment with antihypertensive medication. Patient's self-reports obtained on structured interview correlated best with pill count compliance (r = 0.74, p less than 0.0001). Patients overestimated their compliance by an average of 17% but 90% of those who admitted to being noncompliant were found so. Qualitative urinary chlorthalidone and hydrochlorothiazide levels and changes in serum potassium, uric acid, and blood pressure also correlated with pill count compliance but were less accurate than interviews. Assessment of the patient's "health beliefs" and a variety of sociodemographic and health traits and perceptions did not provide useful information on compliance. Interviewing the patient is a simple and useful approach in assessing compliance with antihypertensive therapy.

Qualitative and quantitative analysis of hydrochlorothiazide in equine plasma and urine by high-performance liquid chromatography

A sensitive, quantitative method has been developed for the determination of hydrochlorothiazide in equine plasma and urine. Thin-layer chromatography is used to screen for the presence of the drug in unknown samples. The TLC screening methods described provide minimum detection limits of 50 ng/mL in plasma and 25 ng/mL in urine. A silica micro chromatography column is used to clean up ethyl acetate extracts for HPLC analysis and mass spectral confirmation. An internal standard, trichloromethiazide, is used to derive quantitative data at concentrations as low as 25 ng/mL for plasma disappearance curves and urinary excretion rates.

Liquid-chromatographic detection of thiazide diuretics in urine

We describe a liquid-chromatographic procedure for detection in urine of all thiazide drugs currently used clinically. Urine is treated initially with NaBH4 to convert any chlorothiazide present to hydrochlorothiazide. The urine is acidified with NaH2PO4 (1.0 mol/L, pH 5), and thiazides are extracted with ethyl acetate. Interfering substances are then removed in two washes with 0.1 mol/L Na2HPO4 at pH 8. The ethyl acetate is evaporated and the residue redissolved in mobile phase. Thiazides are assayed by reversed-phase chromatography, with detection by ultraviolet absorption. Analytical recovery of thiazides ranged from 53 to 93%. Urines from 48 patients were so studied, and the results were compared with results by the currently used spectrophotometric method. The two methods agreed for 56% of samples. Evaluation of the discrepancies by review of patients' histories clearly showed liquid chromatography to have correctly identified seven of eight positive urines that the spectrophotometric method failed to detect. Ultraviolet scanning incorrectly identified as positive two samples, whereas liquid chromatography did not falsely identify any urines as positive. Our method was more sensitive and more specific than the spectrophotometric method.

Correlation of urinary excretion with in vitro dissolution using several dissolution methods for hydrochlorothiazide formulations

Four different hydrochlorothiazide formulations were prepared, and cumulative urinary hydrochlorothiazide excretion was determined in a crossover study using six volunteers. A comparison of in vivo results showed that one formulation (Forumulation D) was significantly different from the others at 2, 3, 4, 5, 8, and 14 hr. A dissolution study was conducted on each formulation using the flask, USP basket, and magnetic basket methods at agitation speeds of 50, 100, and 150 rpm. Formulation D was significantly different from other formulations when determined using the USP basket method at 150 rpm and a sampling time of 10 min; the USP basket method at 100 rpm and a sampling time of 100 min; the flask method at 100 rpm and sampling times of 30, 40, 60, and 120 min; and the flask method at 150 rpm and sampling times of 30 and 40 min. Significant in vitro and in vivo correlations were found using a regression analysis and F test. With a correlation coefficient and 95% confidence intervals, it was established that the USP basket method at 150 rpm was the best predictor of urinary hydrochlorothiazide excretion among the dissolution methods tested.

Estimating compliance with diuretic therapy: urinary hydrochlorothiazide-creatinine ratios in normal subjects

We gave 21 healthy young men 100 mg of hydrochlorothiazide daily to determine whether or not urinary detection of the drug was feasible as a measure of compliance on a standard antihypertensive regimen. All subjects took the drug daily for 6 days, after which they were divided into four groups with differing patterns of medication administration. Urine hydrochlorothiazide and creatinine measurements were obtained to validate the urinary hydrochlorothiazide-creatinine ratio (UHCR) as an accurate quantitative index of compliance. The subjects achieved a constant level of UHCR of 13 +/- 3.0 within 48 hours of hydrochlorothiazide administration. The UHCR levels decreased to 5.0 +/- 0.8 48 hours after discontinuation of the drug (p less than 0.001). UHCR values in the range of 13 +/- 6 indicate that the subject has ingested hydrochlorothiazide 24 hours previously. The UHCR is a potentially useful means of assessing compliance in hypertensive patients taking hydrochlorothiazide.

Pharmacokinetics of hydrochlorothiazide in patients with congestive heart failure

1. Hydrochlorothiazide (HCT, 50-75 mg) was administered orally to seven patients with cardiac failure. 2. Plasma levels and urinary concentration of HCT were determined by GLC. 3. The gastrointestinal uptake of the diuretic in three patients was reduced to approximately half that seen in healthy controls. 4. Plasma halflife of HCT was correlated with endogenous creatinine clearance. 5. Pharmacokinetics of HCT are considerably changed in cardiac failure.

High performance liquid chromatographic analysis of hydrochlorothiazide in serum and urine

We report a high performance liquid chromatographic method for the analysis of hydrochlorothiazide in 500microliter of serum of 25 microliter of urine. The between-day precision of the analysis (CV 5.0-7.0%) is acceptable, as is the recovery of hydrochlorothiazide (90-96%) and trichloromethiazide (96%) added to serum. No drug or drug metabolite interferences have been noted. The method represents a considerable improvement over existing techniques described in the literature.

Malabsorption of hydrochlorothiazide following intestinal shunt surgery

Hydrochlorothiazide 775mg was administered orally to 5 patients who had undergone intestinal shunt operations for obesity 1.5 to 6 years previously. Postoperative weight loss averaged 53.4kg. The concentrations of hydrochlorothiazide in plasma and urine were determined with gas/liquid chromatography. The mean area under the plasma concentration time curve during 9h in 4 of the patients was 889ng/ml.h. Mean total urinary recovery of hydrochlorothiazide amounted to 23.0mg in the 5 patients, which corresponds to approximately half that seen in healthy volunteers. The gastrointestinal hydrochlorothiazide appears to be substantially reduced after intestinal shunt surgery.

Quantitative determination of thiazides in urine by a sensitive colorimetric method

Chloriothiazide and hydrochlorothiazide may be determined in urine by the Bratton-Marshall reaction after extracting with ethyl acetate and treating the extract with Florisil. Such treatment reduces the background color of the urine sample and eliminates interferences. The modified procedure is thus sensitive enough to determine both drugs in 24 hour urine specimens from patients receiving therapeutic doses orally.

[Fluorometric determination of hydrochlorothiazide in body fluids by direct measurement of thin-layer chromatographic plates (author's transl)]

Two fluorometric methods for analysis of hydrochlorothiazide (HCT) are described utilizing direct measurement of thin-layer plates. The first method employs a modification of the Bratton-Marshall reaction and is therefore applicable to all aromatic primary amines. Following diazotation and azocoupling of the HCT hydrolysis product, a fluorescent group is added to the compound. For this purpose N-(1-naphthyl)ethylenediamine is first coupled with 4-chloro-7-nitrobenzo-2,1,3-oxadiazole. In the second method, the intrinsic fluorescence of underivatized HCT, following its extraction from plasma, urine or saliva, is used. It is shown that the sensitivity of this method is sufficient for estimating the kinetics following oral administration of 25 mg HCT.

Identification of selected antihypertensive drugs by thin-layer chromatography

A thin-layer chromatographic procedure is described for the qualitative identification of several antihypertensive drugs including certain thiazide diuretics spironolactone, triamterene, methyldopa and their metabolites. Utilization of new solvent developing systems and spray detecting reagents provides a method useful for the identification of these compounds in biologic fluids at low therapeutic concentrations. Sensitivity limits for these antihypertensive drugs are given, and alternate techniques to provide confirmatory analyses are also presented.