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

Aldosterone receptor antagonists: current perspectives and therapies

Aldosterone is a downstream effector of angiotensin II in the renin-angiotensin-aldosterone system and binds to the mineralocorticoid receptor. The classical view of aldosterone primarily acting at the level of the kidneys to regulate plasma potassium and intravascular volume status is being supplemented by evidence of new "off-target" effects of aldosterone in other organ systems. The genomic effects of aldosterone are well known, but there is also evidence for non-genomic effects and these recently identified effects of aldosterone have required a revision in the traditional view of aldosterone's role in human health and disease. The aim of this article is to review the biological action of aldosterone and the mineralocorticoid receptor leading to subsequent physiologic and pathophysiologic effects involving the vasculature, central nervous system, heart, and kidneys. Furthermore, we outline current evidence evaluating the use of mineralocorticoid receptor antagonists in the treatment of primary aldosteronism, primary hypertension, resistant hypertension, obstructive sleep apnea, heart failure, and chronic kidney disease.

Development and validation of an HPLC method for the determination of spironolactone and its metabolites in paediatric plasma samples

An HPLC method has been developed and validated for the determination of spironolactone, 7 alpha-thiomethylspirolactone and canrenone in paediatric plasma samples. The method utilises 200 microl of plasma and sample preparation involves protein precipitation followed by Solid Phase Extraction (SPE). Determination of standard curves of peak height ratio (PHR) against concentration was performed by weighted least squares linear regression using a weighting factor of 1/concentration2. The developed method was found to be linear over concentration ranges of 30-1000 ng/ml for spironolactone and 25-1000 ng/ml for 7 alpha-thiomethylspirolactone and canrenone. The lower limit of quantification for spironolactone, 7 alpha-thiomethylspirolactone and canrenone were calculated as 28, 20 and 25 ng/ml, respectively. The method was shown to be applicable to the determination of spironolactone, 7 alpha-thiomethylspirolactone and canrenone in paediatric plasma samples and also plasma from healthy human volunteers.

The effect of respiratory disorders on clinical pharmacokinetic variables

Respiratory disorders induce several pathophysiological changes involving gas exchange and acid-base balance, regional haemodynamics, and alterations of the alveolocapillary membrane. The consequences for the absorption, distribution and elimination of drugs are evaluated. Drug absorption after inhalation is not significantly impaired in patients. With drugs administered by this route, an average of 10% of the dose reaches the lungs. It is not completely clear whether changes in pulmonary endothelium in respiratory failure enhance lung absorption. The effects of changes in blood pH on plasma protein binding and volume of distribution are discussed, but relevant data are not available to explain the distribution changes observed in acutely ill patients. Lung diffusion of some antimicrobial agents is enhanced in patients with pulmonary infections. Decreased cardiac output and hepatic blood flow in patients under mechanical ventilation cause an increase in the plasma concentration of drugs with a high hepatic extraction ratio, such as lidocaine (lignocaine). On a theoretical basis, hypoxia should lead to decreased biotransformation of drugs with a low hepatic extraction ratio, but in vivo data with phenazone (antipyrine) or theophylline are conflicting. The effects of disease on the lung clearance of drugs are discussed but clinically relevant data are lacking. The pharmacokinetics of drugs in patients with asthma or chronic obstructive pulmonary disease are reviewed. Stable asthma and chronic obstructive pulmonary disease do not appear to affect the disposition of theophylline or beta 2-agonists such as salbutamol (albuterol) or terbutaline. Important variations in theophylline pharmacokinetics have been reported in critically ill patients, the causes of which are more likely to be linked to the poor condition of the patients than to a direct effect of hypoxia or hypercapnia. Little is known regarding the pharmacokinetics of cromoglycate, ipratropium, corticoids or antimicrobial agents in pulmonary disease. In patients under mechanical ventilation, the half-life of midazolam, a new benzodiazepine used as a sedative, has been found to be lengthened but the underlying mechanism is not well understood. Pulmonary absorption of pentamidine was found to be increased in patients under mechanical ventilation. Pharmacokinetic impairment does occur in patients with severe pulmonary disease but more work is needed to understand the exact mechanisms and to propose proper dosage regimens.

6,7-Dihydroxy-6,7-dihydrocanrenone isomers: improved synthesis and proton NMR study

The synthesis in improved yields of one 6,7-epoxide and three 6,7-dihydroxycanrenone derivatives is described. Canrenone was the starting material for all derivatives and was obtained by acid-catalyzed lactonization of potassium canrenoate. The epoxidation of canrenone to 6 alpha, 7 alpha-epoxycanrenone by m-chloroperbenzoic acid was improved by addition of a free radical inhibitor. This epoxide was efficiently cleaved to 6 beta, 7 alpha-dihydroxy-6,7-dihydrocanrenone by perchloric acid in a dioxane-water mixture; 6 beta, 7 beta- and 6 alpha, 7 alpha-dihydrocanrenone were obtained by OsO4 oxidation of canrenone in either-pyridine and subsequent reduction of the osmates by hydrogen sulfide. The stereochemistry of the products obtained from the reaction of osmium tetroxide with the 6,7-double bond of steroidal 4,6-dien-3-ones has been a controversial issue for some time. A detailed proton-NMR study of the three diol derivatives unequivocally confirmed the proposed stereochemical structure.

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.

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.