Fluorometric microassay for spironolactone and its metabolites in biological fluids

Characterization of spironolactone and metabolites derivatized using Girard's reagent P using mass spectrometry and ion mobility spectrometry

RATIONALE

Spironolactone is a steroidal drug prescribed for a variety of medical conditions and is extensively metabolized quickly after administration. Measurement of spironolactone and its metabolites remains challenging using mass spectrometry (MS) due to in-source fragmentation and relatively poor ionization using electrospray ionization. Therefore, improved methods of measurements are needed, particularly in the case of small sample volumes.

METHODS

Girard's reagent P (GP) derivatization of spironolactone was employed to improve response and provide an MS-based solution to the measurement of spironolactone and its metabolites. We performed ultra-high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UHPLC-ESI-MS/MS) and ion mobility spectrometry (IMS)-high-resolution mass spectrometry (HRMS) to fully characterize the GP derivatization products. Analytes were studied in positive ionization mode, and MS/MS was performed using nonresonance and resonance excitation collision-induced dissociation.

RESULTS

We observed the successful GP derivatization of spironolactone and its metabolites using authentic chemical standards. A signal enhancement of 1-2 orders of magnitude was observed for GP-derivatized versions of spironolactone and its metabolites. Further, GP derivatization eliminated in-source fragmentation. Finally, we performed GP derivatization and ultra-high-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS) in a small volume of murine serum (20 μL) from spironolactone-treated and control animals and observed multiple spironolactone metabolites only in the spironolactone-treated group.

CONCLUSIONS

GP derivatization was proven to have advantageous mass spectral performance (e.g., limiting in-source fragmentation, enhancing signals, and eliminating isobaric analytes) for spironolactone and its metabolites. This work and the detailed characterization using ultra-high-performance liquid chromatography-high-resolution tandem mass spectrometry (UHPLC-HRMS/MS) and IMS serve as the foundation for future developments in reaction optimization and/or quantitative assay development.

Successive ratio subtraction as a novel manipulation of ratio spectra for quantitative determination of a mixture of furosemide, spironolactone and canrenone

Furosemide and spironolactone are commonly prescribed antihypertensive drugs. Canrenone is the main degradation product and main metabolite of spironolactone. Ratio subtraction and extended ratio subtraction spectrophotometric methods were previously applied for quantitation of only binary mixtures. An extension of the above mentioned methods; successive ratio subtraction, is introduced in the presented work for quantitative determination of ternary mixtures exemplified by furosemide, spironolactone and canrenone. Manipulating the ratio spectra of the ternary mixture allowed their determination at 273.6nm, 285nm and 240nm and in the concentration ranges of (2-16μgmL^-1), (4-32μgmL^-1) and (1-18μgmL^-1) for furosemide, spironolactone and canrenone, respectively. Method specificity was ensured by the application to laboratory prepared mixtures. The introduced method was ensured to be accurate and precise. Validation of the developed method was done with respect to ICH guidelines and its validity was further ensured by the application to the pharmaceutical formulation. Statistical comparison between the obtained results and those obtained from the reported HPLC method was achieved concerning student's t-test and F ratio test where no significant difference was observed.

Interfering with mineralocorticoid receptor activation: the past, present, and future

Aldosterone is a potent mineralocorticoid produced by the adrenal gland. Aldosterone binds to and activates the mineralocorticoid receptor (MR) in a plethora of tissues, but the cardiovascular actions of aldosterone are of primary interest clinically. Although MR antagonists were developed as antihypertensive agents, they are now considered to be important therapeutic options for patients with heart failure. Specifically, blocking only the MR has proven to be a difficult task because of its similarity to other steroid receptors, including the androgen and progesterone receptors. This lack of specificity caused the use of the first-generation mineralocorticoid receptor antagonists to be fraught with difficulty because of the side effects produced by drug administration. However, in recent years, several advances have been made that could potentially increase the clinical use of agents that inhibit the actions of aldosterone. These will be discussed here along with some examples of the beneficial effects of these new therapeutic agents.

Development and validation of a dried blood spot-LC-APCI-MS assay for estimation of canrenone in paediatric samples

A selective and sensitive liquid chromatography (LC)-atmospheric pressure chemical ionisation (APCI)-mass spectroscopic (MS) assay of canrenone has been developed and validated employing Dried Blood Spots (DBS) as the sample collection medium. DBS samples were prepared by applying 30 microl of spiked whole blood onto Guthrie cards. A 6mm disc was punched from the each DBS and extracted with 2 ml of methanolic solution of 17alpha-methyltestosterone (Internal Standard). The methanolic extract was evaporated to dryness and reconstituted in acetonitrile:water (1:9, v/v). The reconstituted solution was further subjected to solid phase extraction using HLB cartridges. Chromatographic separation was achieved using Waters Sunfire C18 reversed-phase column using isocratic elution, followed by a high organic wash to clear late eluting/highly retained components. The mobile phase consisted of methanol:water (60:40, v/v) pumped at a flow rate of 0.3 ml/min. LC-APCI-MS detection was performed in the selected-ion monitoring (SIM) mode using target ions at m/z 341.1 and 303.3 for canrenone and internal standard respectively. The selectivity of the method was established by analysing DBS samples from 6 different sources (individuals). The calibration curve for canrenone was found to be linear over 25-1000 ng/ml (r>0.994). Accuracy (% RE) and precision (% CV) values for within and between day were <20% at the lower limit of quantification (LLQC) and <15% at all other concentrations tested. The LLOQ of the method was validated at 25 ng/ml. Clinical validation of the method was achieved by employing the validated method for analysis of 160 DBS samples from 37 neonatal and paediatric patients.

Anti-remodelling effect of canrenone in patients with mild chronic heart failure (AREA IN-CHF study): final results

AIMS

To test whether canrenone, an aldosterone receptor antagonist, improves left ventricular (LV) remodelling in NYHA class II heart failure (HF). Aldosterone receptor antagonists improve outcome in severe HF, but no information is available in NYHA class II.

METHODS AND RESULTS

AREA IN-CHF is a randomized, double-blind, placebo-controlled study testing canrenone on top of optimal treatment in NYHA class II HF with low ejection fraction (EF) to assess 12-month changes in LV end-diastolic volume (LVEDV). Brain natriuretic peptide (BNP) was also measured. Information was available for 188 subjects on canrenone and 194 on placebo. Left ventricular end-diastolic volume was similarly reduced (-18%) in both arms, but EF increased more (P = 0.04) in the canrenone (from 40% to 45%) than in the placebo arm (from 40-43%). Brain natriuretic peptide (n = 331) decreased more in the canrenone (-37%) than in the placebo arm (-8%; P < 0.0001), paralleling a significant reduction in left atrial dimensions (-4% vs. 0.2%; P = 0.02). The composite endpoint of cardiac death and hospitalization was significantly lower in the canrenone arm (8% vs. 15%; P = 0.02).

CONCLUSION

Canrenone on top of optimal treatment for HF did not have additional effects on LVEDV, but it increased EF, and reduced left atrial size and circulating BNP, with potential beneficial effects on outcome. A large-scale randomized study should be implemented to confirm benefits on cardiovascular outcomes in patients with HF in NYHA class II.

Simultaneous determination of spironolactone and its active metabolite canrenone in human plasma by HPLC-APCI-MS

A sensitive and specific liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) method for the simultaneous determination of spironolactone and its active metabolite canrenone in human plasma has been developed and validated. After the addition of estazolam as the internal standard (IS), plasma samples were extracted with methylene chloride : ethyl acetate mixture (20 : 80, v/v) and separated by high-performance liquid chromatography (HPLC) on a reversed-phase C18 column with a mobile phase of methanol-water (57 : 43, v/v). Analytes were determined in a single quadrupole mass spectrometer using an atmospheric pressure chemical ionization (APCI) source. LC-APCI-MS was performed in the selected-ion monitoring (SIM) mode using target ions at m/z 341.25 for spironolactone and canrenone, m/z 295.05 for estazolam. The method was proved to be sensitive and specific by testing six different plasma batches. Calibration curves of spironolactone and canrenone were linear over the range 2-300 ng/ml. The within- and between-batch precisions (relative standard deviation (RSD)%) were lower than 10% and the accuracy ranged from 85 to 115%. The lower limit of quantification (LLOQ) was identifiable and reproducible at 2 ng/ml. The proposed method was successfully applied to study the pharmacokinetics of spironolactone and its major metabolite in healthy male Chinese volunteers.

Simultaneous determination of spironolactone and its metabolites in human plasma

This study describes a specific, precise, sensitive and accurate method for determination of unchanged spironolactone and its major active metabolites in human plasma. After one-step liquid-liquid extraction, analysis of the parent drug and its metabolites was performed in one chromatographic run, using a high performance liquid chromatography (HPLC) method with a programmed switchover of the UV wavelength. Spironolactone and 7 alpha-thiomethyl-spironolactone were detected at 245 nm, while canrenone and internal standard were detected at 280 nm. The column used was an S5 ODS2 (500 mm x 4.6 mm i.d.). The mobile phase was a mixture of acetonitrile-aqueous orthophosphoric acid (pH 3.4). Chromatographic separations were performed at 5 degrees C. The standard curves were linear over the range 10-400 ng ml-1 for spironolactone and 10-600 ng ml-1 for 7 alpha-thiomethyl-spironolactone and canrenone. The precision and accuracy of the method were confirmed by relative standard deviations below 10% for different concentrations, except for the concentration equal to the quantitation limit, where these parameters ranged from 12-15%. The recovery was above 80% for all investigated compounds and for the internal standard. The assay proved to be suitable for pharmacokinetic studies of spironolactone.

High-performance liquid chromatographic determination of spironolactone and its metabolites in human biological fluids after solid-phase extraction

A simple and sensitive high-performance liquid chromatographic procedure to determine spironolactone and its three major metabolites in biological specimens is described. The assay involves sequential extraction on C18 and CN solid phases, and subsequent separation on a reversed-phase column. In plasma samples, spironolactone and its metabolites were completely separated within 8 min using an isocratic mobile phase, while in urine samples a methanol gradient was necessary to achieve a good separation within 14 min. Recoveries for all analytes were greater than 80% in plasma and 72% in urine. Linear responses were observed for all compounds in the range 6.25-400 ng/ml for plasma and 31.25-2000 ng/ml for urine. The plasma and urine methods were precise (coefficient of variation from 0.8 to 12.5%) and accurate (-12.1% to 7.4% of the nominal values) for all compounds. The assay proved to be suitable for the pharmacokinetic study of spironolactone in healthy human subjects.

Conversion of spironolactone to 7 alpha-thiomethylspironolactone by hepatic and renal microsomes

Recent observations indicate that 7 alpha-thiomethylspironolactone is an important circulating metabolite of the mineralocorticoid antagonist spironolactone (SL). Studies were carried out to determine possible sites and pathways of 7 alpha-thiomethyl-SL formation and, in particular, to evaluate SL metabolism by guinea pig hepatic and renal microsomal preparations. In the absence of S-adenosylmethionine (SAM), liver and kidney microsomes rapidly converted SL to 7 alpha-thio-SL as the only metabolite. The rate of 7 alpha-thio-SL production was greater in liver than kidney. In the presence of SAM, 7 alpha-thio-SL was further converted to 7 alpha-thiomethyl-SL by liver and kidney microsomes. The rates of methylation with 7 alpha-thio-SL as substrate were three to four times greater for liver than for kidney, but the Km values were similar (approximately 30 microM) in the two issues. Maximal enzyme activity was obtained with SAM concentrations of 25-200 microM. NADPH had no effect on SL or 7 alpha-thio-SL metabolism by liver or kidney microsomes. To determine if a pathway involving the C-S lyase enzyme might contribute to circulating 7 alpha-thiomethyl-SL levels in vivo, guinea pigs were treated with SL or its dethioacetylated derivative, canrenone, and plasma metabolites were analyzed by HPLC. Both 7 alpha-thiomethyl-SL and canrenone were found to be circulating metabolites in SL-treated animals, but only canrenone was identified in the plasma of canrenone-treated guinea pigs. The results indicate that the liver and kidney are potential sites of 7 alpha-thiomethyl-SL production and that its formation probably does not involve the C-S lyase pathway.

The metabolism and biopharmaceutics of spironolactone in man

Spironolactone, a competitive aldosterone antagonist, has been used for almost 30 years in those disorders associated with primary or secondary hyperaldosteronism. This review is confined to its metabolism and biopharmaceutics in man. Spironolactone undergoes extensive metabolism with no unchanged drug appearing in the urine. Its metabolites can be divided into two main categories: those in which the sulfur of the parent molecule is removed and those in which the sulfur is retained. The dethioacetylated metabolite canrenone, belonging to the former category, was long considered to be the major active metabolite of spironolactone. For this reason pharmacokinetic studies have focussed on its kinetic behaviour. However, pharmacodynamic studies indicated that canrenone could only partly explain spironolactone's action. Furthermore, with the advent of modern high-performance liquid chromatographic techniques to measure canrenone concentrations, it was shown that previously employed assay techniques were unspecific and consequently considerably overestimated true canrenone levels. Recently, it was demonstrated that after a single oral dose of spironolactone, 7 alpha-thiomethylspirolactone is the main metabolite and that unchanged spironolactone reaches maximum serum concentrations which are in the same order of magnitude as canrenone. Both spironolactone and 7 alpha-thiomethylspirolactone are known to possess anti-mineralocorticoid activity, and they may be mainly responsible for the activity of spironolactone. It also appears likely that endocrine side effects of spironolactone, such as gynaecomastia, are mediated by these sulfur-containing compounds. The oral absorption of spironolactone is improved by using micronized drug or inclusion complexes of spironolactone with cyclodextrins. Concomitant food intake has also been shown to enhance the bioavailability, by increasing the absorption and decreasing the first-pass effect of spironolactone.

Determination of the serum concentration of spironolactone and its metabolites by high-performance liquid chromatography

A simple and rapid high-performance liquid chromatographic assay is described for the simultaneous determination in serum of the aldosterone antagonist spironolactone and its metabolites 7 alpha-thiomethylspirolactone, 6 beta-hydroxy-7 alpha-thiomethylspirolactone and canrenone. Ultraviolet absorption at 240 nm was used to detect the different compounds after elution on a normal-phase column. Endogenous serum substances did not interfere with the assay. This method provides a convenient tool in pharmacokinetic studies of spironolactone, in contrast to previously reported aspecific fluorimetric assays or time-consuming thin-layer chromatographic analyses of radioactive biological material.

The influence of age and multimorbidity on the pharmacokinetics and metabolism of spironolactone

The pharmacokinetics of the metabolites of spironolactone (canrenone and fluorigenic metabolites) were investigated in 10 geriatric female patients with multimorbidity after a multiple daily oral administration of 100 mg spironolactone under steady state conditions. The concentration determinations were carried out simultaneously with a specific HPLC method and a less specific fluorimetric method. On comparison of the pharmacokinetic parameters with the respective values of a control group of younger healthy female subjects, the serum concentrations in the elderly patients were found to be twice as high. In addition, a statistically significant positive correlation with age was found in the patients for the kinetic parameters investigated. A positive correlation existed between erythrocyte count and the pharmacokinetic parameters of canrenone, especially with the area under the concentration/time curve. No such association was detectable, however, for the total fraction of fluorigenic metabolites (including canrenone). The results of our investigation indicate that, in addition to the known high binding of canrenone to plasma proteins, there is also possibly a (restrictive) binding to erythrocytes.

The effects of canrenoate K on corticosteroid biosynthesis in nephrectomized dogs

There is evidence from in vitro experiments that spironolactone not only antagonises the peripheral effects of aldosterone but also inhibits the production of corticosteroids by the adrenals. However relevant data from clinical studies are contradictory probably because spironolactone action on the kidneys also activates other mechanisms, such as renin secretion and potassium retention, which are potent stimulants of the adrenal cortex and thus tend to compensate for the inhibition. To determine the inhibitory effect of spironolactone on the adrenals in isolation, three groups of nephrectomized dogs were studied. Steroidogenesis was stimulated either by angiotensin II, potassium, or ACTH infusion. Potassium canrenoate was administered i.v. bolus at the beginning of the experiment. All the groups showed a similar marked decrease in plasma renin activity (PRA). Plasma aldosterone and cortisol were stimulated by the appropriate stimulus but their increase was blunted after the canrenoate K administration. The altered response between the subgroups was statistically significant (P less than 0.05). Plasma progesterone increased after the administration of canrenoate K. The response difference between the respective subgroups was again statistically significant (P less than 0.05). Canrenoate K was rapidly eliminated from the systemic circulation. These data indicate that canrenoate K causes a partial inhibition of aldosterone and cortisol stimulated secretion but augments the plasma levels of the precursor progesterone, as would be expected following inhibition of specific steps of corticosteroid biosynthesis.

Comparison of plasma levels of canrenone and metabolites after base hydrolysis in young and elderly subjects following single and multiple doses of spironolactone

Plasma levels of canrenone and 'total metabolites' after base hydrolysis were compared in young and elderly subjects following single and multiple doses of spironolactone. After the initial dose on Day 1, plasma levels of canrenone and 'total metabolites' were higher in the young than in the elderly group, and significant differences were found between the two age groups in the AUC for both canrenone and 'total metabolites'. However, these differences between the two age groups diminished after multiple dosing on Day 8, and the steady state pre-dose plasma levels of canrenone and 'total metabolites' were significantly higher in the elderly subjects. The accumulation ratios of canrenone and 'total metabolites' were significantly higher in the elderly than in the young subjects. Both canrenone and canrenoic acid were extensively bound to plasma protein, but no differences were found between the two age groups in protein binding. Observed differences in plasma levels after single and multiple dosing between young and old subjects may be consequences of many factors such as a proportionate shift in metabolism with age; impaired oral absorption of the parent compound; and/or altered volume of distribution of the drug.

Pharmacokinetics of canrenone and metabolites after base hydrolysis following single and multiple dose oral administration of spironolactone

The pharmacokinetics of canrenone and 'total metabolites' after base hydrolysis was studied in eight young volunteers following single and multiple dose oral administration of spironolactone. The plasma levels of canrenone and 'total metabolites' were fitted to a two-compartment open model with a first-order absorption process. From our eight normal subjects studied, the harmonic mean of the distributive half-life (t1/2 alpha) of canrenone was found to be 1.66 h, and the harmonic mean of the terminal elimination half-life (t1/2 beta) to be 22.6 h. Harmonic means of the distributive and elimination half-lives of 'total metabolites' after base hydrolysis were 2.48 h and 28.8 h respectively. The accumulation ratio of canrenone was 2.53, whereas that of 'total metabolites' was 1.89. Despite the fact that spironolactone has been shown to induce hepatic metabolism of other drugs, no evidence of autoinduction was noted in the present study, as plasma levels of canrenone and 'total metabolites' were found to obey a linear two-compartment model with reproducible absorption and disposition after single and multiple doses.

Determination of canrenone, the major metabolite of spironolactone, in plasma and urine by high-performance liquid chromatography

An assay procedure for measuring plasma and urine levels of canrenone is described. The drug is extracted with n-hexane-toluene (1:1, v/v) after adding spirorenone as internal standard, and is then separated from plasma constituents and metabolites by high-performance liquid chromatography followed by UV detection at 285 nm. The limit of detection is less than 5 ng/ml. Interference with a series of spironolactone and canrenone metabolites was not observed. Plasma levels and renal excretion of canrenone after oral administration of 200 mg of spironolactone and intravenous injection of 200 mg of potassium canrenoate to a healthy male volunteer were measured.

Stability-indicating methods for quantitative determination of spironolactone using high-pressure liquid chromatography and blue tetrazolium reaction

Stability-indicating methods for the quantitative determination of spironolactone were developed. The methods are based on high-pressure liquid chromatography and a reaction with blue tetrazolium. Both methods are accurate, precise, and sensitive and gave excellent results with commercial tablets, including those containing hydrochlorothiazide in addition to spironolactone, The blue tetrazolium method cannot be used in the presence of high concentrations of either polyethylene glycols or water. Spironolactone decomposition in water or polyethylene glycol appears to follow pseudo-first-order kinetics. The decomposition constant at 65 degrees was 0.0253/day in water versus 0.115/day in polyethylene glycol ointment base USP.

Non-interaction of spironolactone medication and cortisol metabolism in man

In 5 healthy subjects and in 5 patients with decompensated liver diseases, the concentrations of cortisol, canrenone and canrenoate-K were determined after single doses and after a long-term treatment with spironolactone. The concentrations of the metabolites of spironolactone were determined fluorimetrically, those of cortisol by a highly specific radioimmunoassay with previous chromatographic separation. As a result, non-interaction between spironolactone medication and cortisol metabolism, even at high dose and long-term treatment conditions, was established neither in normal test subjects nor in patients with liver failure.

Improved method for comparative evaluation of aldosterone antagonists in healthy man

A method of assessing the qualitative and quantitative activity of competitive aldosterone antagonists in healthy man is described. It requires intravenous infusion of aldosterone (0.5 mg/6 h), iv and oral water loading for six hours and fractionated collection of urine over eight hours. Aldosterone antagonists were administered orally 1.5 h before the start of the infusion (spironolactone 50, 200 or 800 mg) or added to the infused solution (potassium cnarenoate 300, 600 or 1000-1200 mg). The effect was assessed by changes in urinary sodium and potassium excretion and in urinary Na+/K+ ratio. The plasma levels and urinary excretion of canrenone, canrenoate and canrenoate ester glucuronide, respectively, were determined after administration of spironolactone and potassium canrenoate. Between 4-8 h (spironolactone) or 2-8 h (potassium canrenoate) after commencement of the infusion there was linear dose-dependent reversal of the mineralocorticoid-induced sodium retention and/or decrease in the Na+/K+ ratio. The plasma levels and urinary excretion of the metabolites measured were also dose-dependent. The method appears suitable for comparison of the potency of aldosterone antagonists and for defining the time course of drug action within the observation period employed.

Nature of acid-induced fluorescence of 17alpha-methyltestosterone

The fluorescence of the 17alpha-methyltestosterone-trichloroacetic acid reaction product, 1,2,10,15,16,17-hexahydro-10,17,17-trimethylcyclopenta[alpha]phenanthren-3-one, in strong acid was investigated. Structural requirements for fluorescence were derived from absorption and fluorescence studies of related phenanthrenones and cinnamylidene compounds possessing a similar chromophore. All compounds showed fluorescence intensity that was structure and pH dependent. Fluorescence is attributed to both enol and protonated species.

Simultaneous automated determination of spironolactone metabolites in serum

An automated two-phase method for the simultaneous fluorometric determination of the spironolactone metabolites canrenone (II) and canrenoic acid (III) in serum is described. The determination is performed by two dichloroethane extractions of the same serum sample at different pH values. The fluorescence developed in 65% (v/v) sulfuric acid is measured in two separate fluorometers (one each for canrenone and canrenoic acid). Comparable specificity and sensitivity to the manual procedure are obtained, with sensitivity limits of 20 ng of II/ml and of 30 ng of III/ml in serum. This method is applicable to the automated determination of drugs and metabolites in biological material when several extraction steps are involved.

Disposition kinetics of spironolactone in hepatic failure after single doses and prolonged treatment

Six male patients withhistologically characterised, decompensated liver disease who had not previously received spironolactone, were given orally Aldactone 7 mg/kg with 3H-spironolactone 100muCi. The kinetics of the drug were studied in plasma and urine for 6 days. Then, Aldactone 7 mg/kg was given daily for 12 consecutive days, and the pharmacokinetics of a single dose of 3H-spironolactone were re-examined. The kinetics of total radioactivity, as well as of fluorigenic metabolites in plasma, after the first single dose of spironolactone did not differ in patients and normal test subjects; similar percentages of the dose given were excreted within 6 days in urine from patients (47.47 +- 4.88%) and from controls (53.68 +- 2.04%). The kinetics of CH2CI2/H2O distribution coefficients of labelled material in plasma and urine, as well as TLC analysis of the CH2CI2 soluble fraction, revealed no significant differences from controls. After treatment for 12 days with spironolactone, 4 out of 6 patients showed marked acceleration in the rate of elimination of radioactivity from plasma and a corresponding increase in excretion of labelled compounds in urine. Analysis of the excretion products in urine revealed proportionally increased excretion and no evidence of selective induction of a single degradation step. In contrast, delayed elimination was observed in the 2 other patients after 12 days' treatment. However, this was due to dehydration and oliguria caused by over-treatment with the diuretic.

Tissue distribution of 3H-canrenoate potassium in rabbits

Plasma and various organ concentrations of canrenone, canrenoate, and total 3H-activity were measured following single doses of 20 mg of 3H-canrenoate/kg iv to rabbits. Organs studied included heart, lungs, brain, kidneys, liver, adrenal glands, and spleen. Canrenoate was shown to be in rapid equilibrium with canrenone. Both were eliminated from plasma and other tissues with a half-life of about 1 hr. Plasma concentrations of both drugs were equal as early as 10 min after intravenous drug administration. Canrenone was concentrated about 10-fold in organ tissues when compared to plasma, while no such preferential uptake was found with canrenoate. Total 3H-activity declined slowly in all tissues with a half-life of approximately 15 hr, indicating extensive metabolism and metabolite retention in the rabbit.

Pharmacokinetics of spironolactone in man

Five healthy male volunteers received 500 mg Aldactone orally together 100 muCi 3H-20-21-spironolactone; one elderly patient received 1 mCi 3H-spironolactone without additional 'cold' drug. For 6 days the disposition kinetics of the drug were studied in plasma, urine and feces. The tritium concentrations in plasma reached a peak between 25-40 min after administration amounting to 2-3% of the dose/1. Up to the 12th h, they fell rapidly and showed a monoexponential decline (t 1/2: 2.57 +/- 0.27 days) between the 36th and 96th h. Later, a striking increase in the speed of elimination of radioactivity from plasma (t 1/2: 1.66 +/- 0.21 days) was observed. The biological half-life of labeled material in plasma was longer than that of fluorigenic compounds. 47-57% of the dose were excreted in urine and the remaining amount could be detected in feces (total recovery 90%). The half-life of the urinary excretion rate was distinctly shorter (t 1/2: 0.9 +/- 0.11 days) than that of total radioactivity in plasma. This, together with an observed increase of the polar fraction in urine from 35 up to 85%, which was accompanied by a decrease in plasma from 55 to 35%, suggests either tubular reabsorption or enterohepatic recirculation of lipophilic compounds. TLC-separation of the lipophilic fraction in urine revealed two previously unknown compounds of which the main congener was identified as 3-(3-oxo-7 alpha-methylsulfonyl-6 beta, 17 beta-dihydroxy-4-androsten-17 alpha-yl) propionic acid gamma-lactone, as well as canrenone and the metabolites which have already been described (Karim and Brown, 1972; Karim et al., 1975). This metabolite represents the main lipophilic degradation product in urine within the first hours, whereas the 6 beta-OH-7 alpha-methylsulfinyl-spirolactone leveled off and seemed to be and endexcretion product. For further characterisation, the polar fraction was subjected to acidic hydrolysis. The known metabolic pathways of spironolactone degradation are discussed.

High-speed liquid chromatographic determination of canrenone in pharmaceutical dosage forms

Canrenone can be determined by high-speed liquid chromatography in pharmaceutical dosage forms without interference from common excipients or degradation products. This stability-indicating assay, using o-nitroaniline as the internal standard, is rapid and accurate.

Effects of pretreatment with spironolactone of pharmacokinetics of 4'''-methyldigoxin in man

Pharmacokinetics of 3H-4''' -methyldigoxin (md) were studied in three paired experiments with and without pretreatment with spironolactone (7 mg/kg/day for 7 days) and in one additional test person after pretreatment only. The results were compared with controls after oral (n equals 6) and intravenous (n equals 6) administration of md. In addition the biliary excretion of md and its metabolites was investigated in biliary fistula patients with and without pretreatment with spironolactone. After pretreatment of normal persons maximum plasma levels of tritium were approximately 35% lower and they were reached on average 60 min after oral administration as compared with approximately 15 min without pretreatment. Already 12 hrs after oral administration the plasma concentrations, with and without pretreatment, no longer differed and the biological half lives of radioactivity in plasma were equal. With or without pretreatment, the cumulative excretion of tritium in urine and faeces was nearly identical in the paired experiments within 7 days. It was in the range of the controls which eliminated 55.2 +/- 2.8 and 28.6 +/- 5.7% of the dose in urine and faeces, respectively, after oral, and 62.2 +/- 2.1 and 28.9 +/- 5.2%, respectively, after i.v. administration. Accordingly after pretreatment the radioactivity excreted in bile within 48 hrs (14.9% of the dose) did not differ from controls. Examination of the composition of labelled compounds excreted in urine and bile revealed no significant alterations in the metabolic degradation of md under the influence of spironolactone. Thus the profound effects of spironolactone upon pharmacokinetics of md previously observed in rats are without any significance for human conditions.

Aldosterone plasma radioimmunoassay interference by a spirolactone metabolite

The plasma aldosterone radioimmunoassay developed by Ito et al. was found to be non-specific for aldosterone following administration of the spirolactones, spironolactone and canrenoate-K, in rabbits, dogs and humans. The assay interfering principle was identified as a hydroxylated derivative (M-B) of canrenone, which itself is a metabolite common to both spironolactone and canrenoate-K. The metabolite M-B possessed a high cross-reactivity to the 21-hemisuccinate aldosterone antibody relative to other spirolactones. A modified procedure was developed specific for plasma aldosterone in the presence of M-B. Following single doses of spironolactone and canrenoate-K, aldosterone plasma levels were unchanged in humans and in dogs and decreased in rabbits.

Diuretics: mechanism of action and clinical application

Despite the bewildering number of diuretics available to the physician, these drugs can be divided into 4 main groups, characterised by their site of action on sodium reabsorption in the kidney. Drugs acting on the ascending limb of the loop of Henle have a powerful but short acting diuretic effect; they include frusemide, ethacrynic acid and bumetanide. The benzothiadiazines and related compounds have a moderate diuretic action spread over a longer period, whilst the potassium-sparing diuretics, triamterene, amiloride and spironolactone, have only a weak diuretic effect but a marked ability to diminish urinary potassium excretion. The fourth group is made up of miscellaneous substances which function as vasodilator or osmotic agents. The pathogenesis of oedema formation in heart failure is outlined and a logical approach to treatment suggested. Duiretics are being increasingly used in the treatment of non-oedematous states, in particular hypertension, diabetes insipidus and hypercalciuria; their exact role in pregnancy and acute renal failure remains controversial. Side-effects can be related to their effect on electrolyte excretion and include hypokalaemia, hyponatraemia, hyperkalaemia and hyperuricaemia. The incidence of disturbed carbohydrate tolerance in previously normal individuals is low. Other less common side-effects are also discussed.