Determination of chlorthalidone in plasma, urine and red blood cells by gas chromatography with nitrogen detection

The simultaneous UPLC-MS/MS determination of emerging drug combination; candesartan and chlorthalidone in human plasma and its application

A novel, precise, sensitive and accurate ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method has been developed for the simultaneous determination of a novel drug combination, candesartan (CAN) and chlorthalidone (CHL), in human plasma. Chromatographic separation was achieved on Waters Acquity UPLC BEH C₁₈ (50 × 2.1 mm, 1.7 μm). Mobile phase consisting of 1 mm ammonium acetate in water-acetonitrile (20:80 v/v) was used. The total chromatographic runtime was 1.9 min with retention times for CAN and CHL at 0.7 and 1.1 min respectively. Ionization and detection of analytes and internal standards was performed on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and negative ionization mode. Quantitation was done to monitor protonated precursor → product ion transition of m/z 439.2 → 309.0 for CAN, 337.0 → 189.8 for CHL and 443.2 → 312.1 for candesartan D4 and 341.0 → 189.8 for chlorthalidone D4. The method was validated over a wide dynamic concentration range of 2.0-540.0 ng/mL for candesartan and 1.0-180.0 ng/mL for chlorthalidone. The validated method was successfully applied for the assay of CAN and CHL in healthy volunteers.

Collection of biological samples in forensic toxicology

Forensic toxicology is the study and practice of the application of toxicology to the purposes of the law. The relevance of any finding is determined, in the first instance, by the nature and integrity of the specimen(s) submitted for analysis. This means that there are several specific challenges to select and collect specimens for ante-mortem and post-mortem toxicology investigation. Post-mortem specimens may be numerous and can endow some special difficulties compared to clinical specimens, namely those resulting from autolytic and putrefactive changes. Storage stability is also an important issue to be considered during the pre-analytic phase, since its consideration should facilitate the assessment of sample quality and the analytical result obtained from that sample. The knowledge on degradation mechanisms and methods to increase storage stability may enable the forensic toxicologist to circumvent possible difficulties. Therefore, advantages and limitations of specimen preservation procedures are thoroughfully discussed in this review. Presently, harmonized protocols for sampling in suspected intoxications would have obvious utility. In the present article an overview is given on sampling procedures for routinely collected specimens as well as on alternative specimens that may provide additional information on the route and timing of exposure to a specific xenobiotic. Last, but not least, a discussion on possible bias that can influence the interpretation of toxicological results is provided. This comprehensive review article is intented as a significant help for forensic toxicologists to accomplish their frequently overwhelming mission.

Aspects on pharmacokinetics of some diuretics

This review summarizes the present knowledge of some commonly used diuretics. Bendroflumethiazide and bumetanide are completely absorbed from the gut while the uptake of hydrochlorothiazide, chlorthalidone and furosemide averages about 65%. The degree of uptake of amiloride and spironolactone is unknown but exceeds 50%. Plasma t 1/2 of bumetanide and furosemide are approximately 1 h. The clinically important phase of the plasma concentration of bendroflumethiazide has a t 1/2 of 3 h, although a slower phase with a t 1/2 of 9 h has been described. Hydrochlorothiazide and amiloride, often used in combination, both have a t 1/2 of about 10 h. Canrenone, an active metabolite of spironolactone, has a t 1/2 of 15-20 h. Chlorthalidone is eliminated very slowly with a t 1/2 of about two days. This is partly caused by an extensive binding to carbonic anhydrase in the erythrocytes. The protein binding of bendroflumethiazide, bumetanide, canrenone and furosemide is approximately 95%. The binding of chlorthalidone and hydrochlorothiazide is about 75 and 40% respectively. All mentioned diuretics except spironolactone are in part eliminated renally, mainly via tubular secretion. This is the major elimination route for amiloride and hydrochlorothiazide, while it constitutes one third to two thirds for bendroflumethiazide, bumetanide and furosemide. Spironolactone is exclusively eliminated as metabolites.

Determination of Tripamide in human urine by high-performance liquid chromatography and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

Tripamide is a drug widely used in clinical practice for the treatment of hypertension and edema. This work evaluated a screening method for Tripamide and its urinary metabolites in human urine, using high-performance liquid chromatography diode-array detection (HPLC/DAD). Identification of these metabolites was investigated by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) after dosing with 15 mg Tripamide. Acid hydrolysis showed that Tripamide is conjugated in the body. Two suspected metabolites were detected by HPLC/DAD. HPLC/ESI-MS/MS analysis suggested that these metabolites were probably hydroxylated together with loss of the -NH(2) group and dehydrogenation. These results will be useful in confirmation methods for Tripamide in doping control.

Derivatization procedures for gas chromatographic-mass spectrometric determination of xenobiotics in biological samples, with special attention to drugs of abuse and doping agents

The development of low cost MS detectors in recent years has promoted an important increase in the applicability of GC-MS system to analyze for the presence of foreign substances in the human body. Drugs and toxic agents are in vivo metabolized in such a way that more polar compounds are usually formed. Derivatization of these metabolites is often an unavoidable requirement for gas chromatographic analysis. Application of derivatization methods in recent years has been relevant, especially for silylation, acylation, alkylation and the formation of cyclic or diastereomeric derivatives. Given the relevance of drug of abuse testing in modern toxicology, main derivatization procedures for opiates, cocaine, cannabis, amphetamines, benzodiazepines and LSD have been reviewed. Papers describing the analyses of drugs of abuse in matrixes other than blood, such as hair or sweat, have received special attention. Advances in derivatization for sports drug testing have been particularly relevant for anabolic steroids, diuretics and corticosteroids. Among the several methodologies applied, the formation of trimethylsilyl, perfluoroacyl or methylated derivatives have proved to be both versatile and extensively used. Further advances in derivatization for GC-MS applications in clinical and forensic toxicology will depend on the one hand on the degree of further use of GC-MS for routine applications and, on the other hand, on the alternative progress made for developments in LC-MS or CE-MS. Last but not least, the appearance of comprehensive libraries in which reference spectra for different derivatives of many drugs and their metabolites are collected will have an important impact on the expansion of derivatization in GC-MS for toxicological applications.

Simultaneous determination of atenolol and chlorthalidone in plasma by high-performance liquid chromatography. Application to pharmacokinetic studies in man

An HPLC method developed to detect in a single run both atenolol and chlorthalidone, extracted from plasma, using two detectors (UV for chlorthalidone and fluorometric for atenolol) connected in series, is described. The drugs were separated on an ODS column at room temperature using a 0.05 M sodium dodecyl sulphate in phosphate buffer (pH 5.8)-n-propanol (95:5, v/v) solution, delivered at a flow-rate of 1.3 ml/min. Having ascertained the sensitivity (10 ng/ml of both drugs) and the intra-day reproducibility (pre-study validation), the reliability of the method was verified by inter-day assays (within-study validation) carried out during the analysis of plasma samples collected from healthy volunteers after single-dose treatment with atenolol+chlorthalidone tablets (pharmaceutical preparations containing 100+25 mg and 50+12.5 mg of the two drugs, respectively).

Detection of diuretic agents in doping control

Since the inclusion of diuretics in the list of banned substances in sports in 1988, a large number of screening and confirmation procedures to detect the presence of these substances in urine samples have been developed. In this paper, a review of the analytical methodology described to analyze diuretics is presented. The paper has been focused on the needs of doping control and mainly screening procedures including sample preparation and liquid or gas chromatographic separation have been considered. More relevant papers using capillary zone electrophoresis have been also considered. Mass spectrometry is mandatory in doping control for confirmation purposes, and finally, mass spectrometric techniques described for diuretics have been reviewed.

Obesity, glucose intolerance, hyperinsulinemia, and response to antihypertensive drugs

Responsiveness to antihypertensive medications was investigated cross-sectionally in 559 individuals comprising all treated hypertensive patients identified within a representative sample (n = 3,532, aged 40-70 years) of the Jewish population in Israel. A rate of dosage score (a summed ranking of dosages of all drugs taken) of two or more increased significantly with increasing levels of body mass index (BMI) from 37.5% in levels less than 23, 54.9% in levels 23.0-29.9, and 76.4% in levels of 30 or greater (p less than 0.0001). Multivariate analyses, adjusting for age, gender, arm circumference, and ethnic group, confirmed the independent effect of BMI on dosage score (p less than 0.001). At each level of dosage score, mean blood pressure levels were equivalent at all levels of BMI after adjusting for potential confounders. This indicates that achieved blood pressure level and not BMI itself was the main determinant of the higher dosing regimens prescribed at higher levels of BMI. In representative subgroups, glucose tolerance (n = 372) and hyperinsulinemia (n = 190) were determined and were found to be positively associated with a dosage score of two or more (p less than 0.05) independently of BMI. These effects could not be accounted for by poor compliance or by altered drug absorption or disposition since overnight urinary drug excretion and plasma drug concentrations 2 hours after ingestion, measured in 80 randomly selected patients from the study group, were not different across BMI categories at similar dosages.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of diuretic doping agents by HPLC screening and GC-MSD confirmation

The simultaneous analysis of 14 diuretics in human urine (belonging to five different pharmacological groups) by reversed-phase high-performance liquid chromatography (HPLC) with a diode-array detector was developed by using a gradient elution with acetonitrile and phosphate buffer containing propylamine hydrochloride on a Bondclone-ODS (10 microns) column. The method was applied to the screening test of several diuretics abused by athletes. The confirmation analysis was performed by gas chromatography-mass spectrometry with ion-selective detection (GC-MSD). The characteristic mass fragment ions obtained by electron-impact (EI) ionization (70 eV) provided sufficient identification of these diuretic agents. During the 1990 weight-lifting contest of Asia in Kao-Hsiung, Republic of China, one urine sample was found positive for the diuretic hydrochlorothiazide.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

Diuretics. Clinical pharmacology and therapeutic use (Part I)

25 years have elapsed since the introduction of the first effective oral diuretic, chlorothiazide. Diuretics are now amongst the most widely prescribed drugs in clinical practice worldwide. Availability of these drugs has not only brought therapeutic benefit to countless numbers of patients but it has at the same time provided valuable research tools with which to investigate the functional behaviour of the kidney and other electrolyte-transporting tissues. Despite many remaining gaps in our knowledge of the biochemical processes involved in diuretic drug action, available compounds can be divided into 5 groups on the basis of their preferential effects on different segments of the nephron involved in tubular reabsorption of sodium chloride and water. Firstly, there is heterogeneous group of chemicals that share the common property of powerful, short-lived diuretic effects that are complete within 4 to 6 hours. These agents act on the thick ascending limb of Henle's loop and are known as 'high ceiling' or 'loop' diuretics. The second group are the benzothiadiazines and their many related heterocyclic variants, all of which localise their effects to the early portion of the distal tubule. The third group comprises the potassium-sparing diuretics which act exclusively on the Na+-K+/H+ exchange mechanisms in the late distal tubule and cortical collecting duct. The action of drugs in groups 2 and 3 is prolonged to between 12 and 24 hours. The fourth group consists of diuretics that are chemically related to ethacrynic acid but have the unusual property of combining within the same molecule the property of saluresis and uricosuria. These compounds have actions, to different individual extents, in the proximal tubule, thick ascending limb, and early distal tubule and are known as 'polyvalent' diuretics. Finally, there is a mixed group of weak or adjunctive diuretics which includes the vasodilator xanthines such as aminophylline, and the osmotically active compounds such as mannitol. Available evidence on the molecular mechanisms of action of diuretics in each group is reviewed. The haemodynamic, humoral and physical factors involved in control of electrolyte and fluid handling by the kidney in normal conditions and pathological states are discussed in relation to rational choices of different diuretics in the treatment of various oedematous and non-oedematous conditions.

Derivatization reactions in the gas—liquid chromatographic analysis of drugs in biological fluids

Alkylation, acylation, silylation and other derivatization reactions applied to the gas chromatographic analysis of drugs in biological matrices are reviewed. Reaction conditions are discussed in relation to reaction mechanisms. Detector-oriented labelling of drugs, and derivatization with chiral reagents for the separation of enantiomers are surveyed. Data on the sample clean-up, derivatization and GLC analysis of more than 300 drugs and related compounds are listed.

Alkylation with alkylhalides as a derivatization method for the gas chromatographic determination of acidic pharmaceuticals

The various types of alkylation reactions with alkyl halides and their application in the gas chromatographic analysis of acidic compounds of pharmaceutical interest are reviewed. An extensive survey of the use of these methods for the analysis of various (classes of) compounds is given, with special reference to their determination in biological matrices.

Changes in intrarenal sodium handling during saluretic treatment in patients with essential hypertension

The effect of 50 mg chlorthalidone on blood pressure, body fluid volumes and renal functional parameters was determined in 8 patients with essential hypertension. After 3 days there were signs of volume depletion with little change in mean arterial pressure (MAP). Maximal free water clearance (CH2O) was decreased and fractional proximal sodium reabsorption was increased, but no correlations between these parameters were found. After 3 months there was in inverse relationship between both changes in MAP and the indices of volume depletion and CH2O. It is concluded that when MAP decreases after prolonged saluretic treatment, there is a partial recovery of the initially induced volume depletion and less stimulation of proximal tubular sodium reabsorption. The continuing inhibitory action of chlorthalidone on "distal" sodium reabsorption is partially compensated for, probably by the stimulating effect at this site of the decrease in MAP.

Haemodynamic and hormonal changes during acute and chronic diuretic treatment in essential hypertension

The short- and long-term effects of diuretic treatment with chlorthalidone 50 mg/day on haemodynamic and hormonal parameters in patients with essential hypertension (WHO grade I) were investigated. After three days of treatment, all patients showed a rise in plasma renin activity (PRA), plasma aldosterone (PA), urinary norepinephrine excretion (UNE) and heart rate (HR), and a decrease in body weight (BW) and extracellular volume (ECV) and blood volume (BV); the change in blood pressure (BP) was variable. The changes in BP were correlated with those in BV. After three months of therapy, the signs of volume depletion tended to fade, but the lower ECV persisted. In contrast to the 4-day study, after three months the change in BP correlated inversely with changes in ECV and renin dependency (saralasin response), and positively with PRA and changes in UNE. It is concluded that the BP response to diuretic treatment is determined by the adaptation with time of the haemodynamic reactions to the volume-depleted state. Whether this adaptation will take place cannot be predicted from the control values of the parameters studied, or from acute changes observed during the first days of treatment.

The distribution of chlorpromazine between plasma and erythrocytes

Chlorpromazine is found to be taken up by the erythrocytes in a dissociable binding similar to that of the plasma protein binding so that an equilibrium is attained between these binding sites. The plasma/cell ratio is on an average 2 but is subject to large interindividual variations. This ratio is only moderately influenced by the presence of other drugs and anticoagulants in the blood. The consequences of the cell binding of drugs for the analytical result when using plasma or whole blood and the evaluation of blood concentrations of their relation to the therapeutic effect are discussed.

Biliary excretion of chlorthalidone in humans

A single oral dose of the diuretic chlorthalidone (100 or 200 mg) was given to six cholecystectomized patients with T-tube drainage of the common bile duct, and the 24 h bile and urine were collected during 3--7 days. Urinary recovery of chlorthalidone was 23--27 per cent of the dose, which is in the range of that in healthy volunteers. Chlorthalidone concentration in bile was 11--44 times lower than urine concentration in corresponding periods, and biliary recovery was only 0.6--1.4 per cent of the dose. When compared from equal periods of sampling of bile and urine, the same relative amount of drug was found in bile, whether the 100 or 200 mg dose had been given (viz., a fraction of 2.5--4.7 per cent and 2.5--5.7 per cent of corresponding urinary amounts respectively). It was concluded that excretion into bile constitutes only a minor route of elimination for unchanged chlorthalidone. Bile samples treated with glucuronidase and sulphatase showed no increase of chlorthalidone concentration. The open acid analogue of chlorthalidone, 3-(4-chloro-3-sulphamoylbenzoyl)-benzoic acid, was apparently not formed as a human metabolite, as evidenced by gas chromatographic analysis of both urine and bile.

Differential potentiometric method for determining dissociation constants of very slightly water-soluble drugs applied to the sulfonamide diuretic chlorthalidone

A renewed application of potentiometric acid-base titrations is described, by which dissociation constants of practically water-insoluble drugs can be measured accurately. The method uses the difference in the amount of titrant between a suitable aqueous solvent and a solution of the drug in that solvent. Such potentiometric difference titrations were conducted on a 3.7 X 10(-4) M solution of chlorthalidone in 0.1 M aqueous KCl in the pH 3.5--10.6 range at 25 degrees. Nonlinear least-squares regression analysis was applied to the data. From four determinations, a value of 9.24 +/- 0.02 (mean +/- SEM) resulted for the apparent dissociation constant of the first chlorthalidone acid group. The thermodynamic dissociation constant was calculated at pKa1 = 9.35 (25 degrees) by using a correction for activity.

Automated analysis of chlorthalidone

Chlorthalidone inhibition of the enzymatic hydrolysis rate of p-nitrophenyl acetate by bovine erythrocyte carbonic anhydrase was used as a basis for chlorthalidone determination in plasma and urine. For urinary samples, a completely automated, continuous flow system was developed to extract the samples and perform the enzymatic reaction. Over 100 samples per day could be assayed by one person. The assay had a sensitivity of 0.5 micrograms/ml and thus could determine urinary concentrations after a therapeutic chlorthalidone dose. To determine plasma concentrations after a therapeutic dose, a manual extraction procedure was used in combination with a second continuous flow system for the enzymatic reaction. This system was optimized to detect the lowest chlorthalidone concentration allowed by the enzymatic inhibition constant and could detect 25 ng/ml.

Absolute bioavailability of chlorthalidone in man: a cross-over study after intravenous and oral administration

Seven normal human volunteers each received a constant-rate infusion of chlorthalidone for 2 h, and the same (commonly 50 mg) single oral dose on separate occasions. The concentration of unchanged chlorthalidone was analyzed over a 100 to 220 h period in plasma, red blood cells, urine and faeces after both dosage forms. A three compartment model was required to describe the intravenous plasma concentrations in five of the subjects. A two compartment model sufficed to account for the decay of the oral plasma concentrations in all seven subjects. The mean plasma t1/2 after i.v. dosing was 36.5 h (+/- 10.5 SD), and the mean plasma t1/2 after oral doses was 44.1 h (+/- 9.6 SD). The mean red blood cell concentration t1/2 after i.v. doses was 46.4 h (+/- 9.9 SD), and the mean red blood cell t1/2 after the oral doses was 52.7 h (+/- 9.0 SD). The shorter i.v. half-live was not equally manifest in all subjects, being mainly apparent in three of them. In all cases the urinary excretion rate plots were parallel to the plasma concentration curves. As the faster decay after i.v. administration was not accompanied by increased renal clearance, the difference must have been due to non-renal mechanism. The mean total of 65.4 (+/- 8.6 SD) % of the intranvenous dose was excreted in urine over infinite time, whereas the mean total excretion after the oral dose was 43.8 (+/- 8.5 SD) %. Faecal excretion ranged from 1.3--8.5% of dose in the i.v. study to 17.5--31.2% of dose in the oral study. The sum of the amounts present in urine plus faeces pointed strongly to an important metabolic route of elimination of chlorthalidone. Bioavailability estimates (F) from three sets of data were--a mean F of 0.61 from plasma concentrations, 0.67 from urinary excretion measurements and 0.72 from the erythrocyte concentrations. Simulations with a non-linear model indicated lesser validity of the estimate from erythrocyte concentrations. It was concluded that the average of plasma and urine data, F = 0.64, yielded the best estimate of the oral availability of chlorthalidone 50 mg in man.