Spironolactone (1 mg/day) exerts anti-androgenic activity in rats. A single pretreatment of spironolactone (1 mg/rat) inhibits specific and saturable uptake of hormone into prostate induced by tracer dose administration of [3H]testosterone.

Absorption, Distribution and Excretion
In healthy volunteers, the mean time to peak plasma concentrations of spironolactone and its active metabolite canrenone was 2.6 hours and 4.3 hours, respectively. Food increases the bioavailability of spironolactone (as measured by AUC) by approximately 95.4%. Metabolites are primarily excreted in the urine, followed by bile. Spironolactone metabolites are mainly excreted in urine (42-56%) and feces (14.2-14.6%). Unmetabolized spironolactone is not found in urine. When spironolactone was first introduced into clinical use, its bioavailability was insufficient, which was improved by formulating it into fine powder or micronized dosage forms. Its absolute bioavailability is indirectly estimated to be approximately 73%, and food can improve its bioavailability. Almost all absorbed spironolactone (>90%) is bound to plasma proteins, and steady state is reached within 8 days after repeated administration. Following oral administration of 100 mg, spironolactone had a plasma half-life of 1–2 hours, a peak time of 2–3.2 hours, a maximum plasma concentration of 92–148 ng/mL, an area under the concentration-time (0–24 hours) curve of 1430–1541 ng/mL/hour, and an elimination half-life of 18–20 hours. In male rats, female dogs, and female monkeys, the in vivo distribution of (14)C spironolactone was investigated after intravenous or oral administration of 5 mg/kg body weight. The estimated gastrointestinal absorption rates in rats, dogs, and monkeys were 82%, 62%, and 103%, respectively. Spironolactone was extensively metabolized in all three animal groups, with metabolites primarily excreted in urine and feces. The excretion of the radiolabeled substance in urine or feces was similar in all three animals after intravenous and oral administration. Similar to humans, monkeys excrete roughly equal amounts in urine and feces, while rats and dogs primarily excrete it in feces due to bile excretion. Following oral administration, the percentages of urinary excretion in rats, dogs, and monkeys were 4.7%, 18%, and 46%, respectively. The high excretion (90%) of the radiolabeled substance in feces after intravenous injection in rats indicates the importance of bile excretion in this species. Biotransformation of spironolactone also varies by species. …
The absorption of spironolactone in the gastrointestinal tract depends on the formulation. Currently available spironolactone formulations are well absorbed in the gastrointestinal tract, with bioavailability exceeding 90% compared to the optimally absorbed polyethylene glycol 400 spironolactone solution. Peak serum concentrations of spironolactone are reached within 1–2 hours after a single oral dose, while peak serum concentrations of its main metabolite are reached within 2–4 hours. Compared to the fasting state, when taken with food, the peak serum concentrations and area under the serum concentration-time curve (AUC) of the drug and its major metabolite were significantly increased…
Spinolactone and its major metabolite canrenone both have plasma protein binding rates exceeding 90%. Spironolactone or its metabolites may cross the placenta. Canrenone, the major metabolite of spironolactone, is distributed into breast milk.
Metabolism/Metabolites
Spironolactone is rapidly and extensively metabolized, generating a variety of metabolites. One class of metabolites is formed after the desulfurization of spironolactone, such as canrenone. Another class of metabolites retain sulfur, including 7-α-thiomethylspironolactone (TMS) and 6-β-hydroxy-7-α-thiomethylspironolactone (HTMS). Spironolactone is first deacetylated to 7-α-thiospironolactone. 7-α-thiospironolactone is S-methylated to TMS (the major metabolite), or desulfurized and acetylated to canrenone. Both TMS and HTMS can be further metabolized. In humans, the potency of TMS and 7-α-thiospironolactone in reversing the synthesis of the mineralocorticoid fludrocortisone influencing urinary electrolyte composition is approximately one-third that of spironolactone. However, since serum concentrations of these steroids are not measured, incomplete absorption and/or first-pass metabolism cannot be ruled out as contributing factors to their reduced activity in vivo. Spironolactone is rapidly and extensively metabolized into compounds excreted in urine and feces. It undergoes enterohepatic circulation, but the unchanged drug is not found in urine or feces. Spironolactone metabolites can be divided into two main categories: one retaining the sulfhydryl group, and the other removing the sulfhydryl group through desulfaacetylation. For many years, the desulfaacetylated metabolite canrenone was considered the major metabolite; however, using more precise analytical methods such as high-performance liquid chromatography (HPLC), 7α-thiomethylspironolactone has been identified as the major metabolite of spironolactone. The metabolite is hydrolyzed from the thioacetate group to 7α-thiospironolactone (as an intermediate), which is then S-methylated to 7α-thiomethylspironolactone. The latter can be further hydroxylated to 6β-hydroxy-7α-thiomethylspironolactone, and oxidized to 7α-methylsulfinylspironolactone and 7α-methylsulfinylspironolactone, or sulfoxide-treated to 6α-hydroxy-7α-methylsulfinylspironolactone and 6β-hydroxy-7α-methylsulfinylspironolactone. In the formation of the sulfur desulfurization metabolite, 7α-thiomethylspironolactone is first desulfurized and acetylated to canrenone, which is further metabolized through three pathways: first, hydrolysis of the γ-lactone ring to canrenic acid, which is excreted in urine as a glucuronide ester; second, hydroxylation to 15α-hydroxycanrenone; and finally, reduction to various dihydro, tetrahydro, and hexahydro derivatives. Canrenone and canrenic acid are in equilibrium. Spironolactone and its various metabolites are all biologically active; in descending order of activity, they are 7α-thiospironolactone, 7α-thiomethylspironolactone, and canrenone.
Species differences exist in the biotransformation of spironolactone. In the plasma of rats and dogs, canrenone is the major extractable metabolite; while in monkeys and humans, canrenone and a highly polar, unidentified metabolite are the major components. Canrenone is the major component in the urine of all four animal groups. Significant species differences exist in the metabolites of spironolactone in feces, with the metabolite pattern in dog feces significantly different from that in rats, monkeys, or humans. Overall, the conclusion is that the distribution and metabolism of spironolactone in monkeys are most similar to those in humans compared to rats or dogs.
Six spironolactone metabolites were detected in the urine of treated subjects. .../One of them is/the desulfurized acetylated compound canrenone, γ-lactone 3-(3-oxo-17β-hydroxy-4,6-androsadien-17α-yl)propionic acid...
The concentration of canrenone in breast milk of a 28-year-old woman after taking 25 mg of spironolactone (Aldactone) twice daily was determined by fluorescence method.
Spionolactone is rapidly and extensively metabolized. Its metabolic pathway is complex and can be divided into two main pathways: one is the pathway that retains the sulfhydryl group, and the other is the pathway in which the sulfhydryl group is removed through desulfurization acetylation. Spironolactone is converted into an active metabolite that can inactivate adrenal and testicular cytochrome P450 enzymes. It also has anti-androgenic activity.
Excretion pathway: The metabolite is mainly excreted in urine, and secondarily in bile.
Half-life: 10 minutes

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Biological half-life
The average half-life of spironolactone is 1.4 hours. Its metabolites (including canrenone, TMS, and HTMS) have mean half-lives of 16.5 hours, 13.8 hours, and 15 hours, respectively. Almost all absorbed spironolactone (>90%) is bound to plasma proteins, and steady state is reached within 8 days after repeated dosing. After oral administration of 100 mg, the plasma half-life of spironolactone is 1–2 hours, the time to peak concentration is 2–3.2 hours, the maximum plasma concentration is 92–148 ng/mL, the area under the concentration-time (0–24 hours) curve is 1430–1541 ng/mL/hour, and the elimination half-life is 18–20 hours. In healthy adults, after a single oral dose, the mean half-life of spironolactone is 1.3–2 hours, and the mean half-life of 7α-thiomethylspironolactone is 2.8 hours. Canrenone has been reported to have a half-life of 13–24 hours. In multiple-dose studies, the mean steady-state plasma elimination half-life of canrenone was 19.2 hours when 200 mg of the drug was taken once daily; and the mean steady-state plasma elimination half-life of canrenone was 12.5 hours when 200 mg of the drug was taken in four equal doses daily.

Toxicity Summary
Spironolactone is a specific aldosterone antagonist that exerts its effects primarily through competitive binding to receptors at aldosterone-dependent sodium-potassium exchange sites in the distal renal tubules. Spironolactone increases sodium and water excretion while retaining potassium. Through this mechanism, spironolactone has both diuretic and hypotensive effects. It can be used alone or in combination with other diuretics that act on the proximal renal tubules. Aldosterone interacts with cytoplasmic mineralocorticoid receptors, enhancing the expression of Na+,K+-ATPases and sodium channels involved in sodium-potassium transport in the distal renal tubules. Spironolactone binds to these mineralocorticoid receptors, blocking the effects of aldosterone on gene expression. Aldosterone is a hormone; its primary function is to retain sodium and excrete potassium in the kidneys. Hepatotoxicity
Clinically significant liver injury caused by spironolactone is rare, with only a few case reports. Liver injury usually appears 4 to 8 weeks after treatment, and the pattern of elevated serum enzymes is usually hepatocellular or mixed. Allergic reactions (rash, fever, eosinophilia) and the formation of autoantibodies are rare. They recover within 1 to 3 months after discontinuation of the drug, and all cases are mild and self-limiting (Case 1). Probability score: D (likely a rare cause of clinically significant liver injury). Effects during pregnancy and lactation ◉ Overview of use during lactation Limited data suggest that spironolactone is rarely excreted into breast milk. There have been reports of no adverse effects on infants of mothers who breastfed while taking spironolactone. Use of spironolactone during lactation appears to be acceptable. ◉ Effects on breastfed infants One mother took 25 mg of spironolactone four times daily from pregnancy, and her 17-day-old infant (not specified on the degree of breastfeeding) maintained normal serum sodium and potassium levels. [1] One mother took 75 mg of spironolactone orally every other day while breastfeeding. She also took 400 mg of benzyl tosylate every 8 hours, 25 mg of atenolol daily, 20 mg of propranolol three times daily, and supplemented with multivitamins, potassium, and magnesium. The infant developed jaundice 60 hours after birth, which was thought to be unrelated to the medication, but subsequently subsided. The infant's weight gain and development were normal in the first four months after birth. [2]
A transgender woman took spironolactone 50 mg twice daily to suppress testosterone; domperidone 10 mg three times daily, later increased to 20 mg four times daily; oral micronized progesterone 200 mg once daily; oral estradiol 8 mg once daily; and pumped milk 6 times daily to promote lactation. After 3 months of treatment, the estradiol regimen was changed to a 0.025 mg patch daily, and the progesterone dose was reduced to 100 mg daily. Two weeks later, she began exclusively breastfeeding her partner's newborn. Exclusive breastfeeding lasted for 6 weeks, during which the infant's growth and bowel habits were normal. The patient continued to partially breastfeed the infant for at least 6 months. [3]
A woman with Gitmann syndrome took spironolactone (dosage not specified) and potassium and magnesium supplements for at least 4 months while breastfeeding her infant. No adverse effects on the infant were reported. [4]
◉ Effects on lactation and breast milk
Strong diuretic effects can inhibit lactation;[5,6]However, spironolactone alone is unlikely to produce such a strong inhibitory effect.
Spinolactone can cause gynecomastia. The estimated risk was 52 cases per 1000 patients treated, which is 8.4 times the baseline risk. [7]
A transgender woman was receiving gender affirmation therapy and was taking 4 mg of estradiol sublingually twice daily, 100 mg of spironolactone sublingually twice daily, and 200 mg of progesterone at bedtime. In preparation for her partner's delivery, the patient increased the sublingual estradiol dose to 6 mg twice daily and the progesterone dose to 400 mg at bedtime. Domperidone was started at 10 mg twice daily to increase serum prolactin levels, which was then increased to 20 mg four times daily. Before delivery, progesterone was discontinued, spironolactone was reduced to 100 mg daily, and estradiol was switched to transdermal administration at 25 μg daily. On postpartum day 59, estradiol was switched to sublingual administration at 2 mg daily, and spironolactone was increased to 100 mg twice daily. Patients secreted up to 240 mL of milk daily, containing typical macronutrient and oligosaccharide levels. [8]

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Protein Binding
Spinolactone and its metabolites bind to plasma proteins in more than 90% of their volume. Spironolactone and canrenone can bind to serum albumin and α1-acid glycoprotein.

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Toxicity Data
The oral LD50 of spironolactone in mice, rats, and rabbits is greater than 1000 mg/kg.
Studies have shown that aspirin can slightly reduce the natriuretic effect of spironolactone in healthy individuals, possibly by reducing the active tubular secretion of the active metabolite canrenone. However, the antihypertensive effect of spironolactone and its effect on urinary potassium excretion in hypertensive patients appear to be unaffected. Patients receiving either drug should be monitored for a decrease in clinical response to spironolactone until more clinical data on this potential interaction are available.
Spinolactone has been reported to reduce vascular responsiveness to norepinephrine; therefore, patients receiving spironolactone should use regional or general anesthesia with caution.
In a preliminary study, 70 female Sprague-Dawley rats (approximately 50 days old, weighing 150–180 g) were administered a single dose of 40 mg of 7,12-dimethylbenzo[a]anthracene (DMBA) dissolved in 2 mL of corn oil via gavage. In one study, 20 rats received pharmaceutical-grade spironolactone via gavage at a dose of 100 mg/kg body weight, dissolved in 1 mL of distilled water, twice daily for 7 days, starting 4 days prior to DMBA administration. The study was terminated after 150 days of DMBA treatment, and the incidence of mammary tumors was determined by palpation. The incidence of palpable mammary tumors decreased from 21/24 in the DMBA-only group to 3/14 in the DMBA-spironolactone combined group. In a second experiment, 80 female Sprague-Dawley rats received 2 mg DMBA (dissolved in 0.4 mL of oil emulsion) intravenously via the jugular vein once daily on days 1, 4, and 7. Two days prior to the first DMBA injection, 40 of these rats received pharmaceutical-grade spironolactone via oral gavage twice daily for 12 consecutive days at a dose of 100 mg/kg body weight, dissolved in 1 mL of distilled water. At the end of the study, 147 days after the start of DMBA treatment, autopsy revealed mammary tumors in 32 of the 32 rats treated with DMBA alone, compared to 23 of the 36 rats treated with DMBA in combination with spironolactone (p < 0.001). Salicylate may reduce renal tubular secretion of canrenone, thereby reducing the diuretic effect of spironolactone, while spironolactone may alter the clearance of digitalis. For more complete data on spironolactone interactions (13 items in total), please visit the HSDB record page.

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Non-human toxicity values
Rat intraperitoneal LD50: 277 mg/kg
Mouse intraperitoneal LD50: 260 mg/kg
Rabbit intraperitoneal LD50: 866 mg/kg
Rabbit oral LD50: > 1000 mg/kg
For more complete non-human toxicity data on spironolactones (6 in total), please visit the HSDB record page.

J Biol Chem.2010 Sep 24;285(39):29932-40;Mol Cell Endocrinol.1974 Dec;2(1):59-67.

Therapeutic Uses
Aldosterone antagonists; diuretics
/EXPL THER:/ Aldosterone plays a crucial role in the pathophysiology of heart failure. In a double-blind study, we enrolled 1663 patients with severe heart failure, left ventricular ejection fraction not exceeding 35%, who were receiving angiotensin-converting enzyme inhibitors, loop diuretics, and (in most cases) digoxin. A total of 822 patients were randomized to receive 25 mg spironolactone daily, and 841 patients received placebo. The primary endpoint was all-cause mortality. The trial was terminated early after a mean follow-up period of 24 months due to the effectiveness of spironolactone determined in the interim analysis. There were 386 deaths (46%) in the placebo group and 284 deaths (35%) in the spironolactone group; relative risk of death 0.70; 95% confidence interval 0.60 to 0.82; P < 0.001). The risk of death was reduced by 30% in the spironolactone group, attributed to a decrease in the risk of death from progressive heart failure and sudden cardiac death. The frequency of hospitalization due to worsening heart failure was 35% lower in the spironolactone group than in the placebo group (relative risk of hospitalization 0.65; 95% confidence interval 0.54 to 0.77; P<0.001). Furthermore, patients receiving spironolactone showed significant improvement in heart failure symptoms according to the New York Heart Association (NYHA) functional classification (P<0.001). In men receiving spironolactone, 10% reported gynecomastia or breast pain, compared to 1% in the placebo group (P<0.001). The incidence of severe hyperkalemia was extremely low in both groups.
Veterinary use: Spironolactone can be used in combination with furosemide to control ascites.
Veterinary use: Spironolactone is the most commonly used drug and is a competitive antagonist of aldosterone. In animals with congestive heart failure, the renin-angiotensin system is activated due to hyponatremia, hyperkalemia, and decreased blood pressure or cardiac output, leading to elevated aldosterone levels. Aldosterone is responsible for increasing the reabsorption of sodium and chloride by the renal tubules and the excretion of potassium and calcium. Spironolactone competes with aldosterone for receptor sites, resulting in mild diuresis and potassium retention. For more complete data on the therapeutic uses of spironolactone (12 in total), please visit the HSDB record page.
Drug Warnings
Spironolactone is an aldosterone antagonist that acts on mineralocorticoid receptors. It is a potassium-sparing diuretic, and hyperkalemia is the most common and potentially serious complication of its treatment. Impaired renal function appears to increase this risk, as does potassium chloride supplementation. Excessive diuresis can also lead to dehydration and hyponatremia. In addition, several endocrine effects have been reported, the most common being gynecomastia, with an incidence ranging from 7% to 52% that is dose-related. This side effect is reversible and disappears upon discontinuation of the drug. Other endocrine effects include decreased male sexual function and menstrual irregularities, amenorrhea, breast tenderness, and melasma in women. These effects may be related to the interaction between spironolactone and androgen receptors. A few case reports of idiosyncratic drug reactions have been reported, including one case of hepatitis and several cases of agranulocytosis. Approximately 10 cases of allergic contact dermatitis have been reported following topical application of spironolactone to treat various skin conditions (involving its anti-androgenic activity). Maternal use generally compatible with breastfeeding: Spironolactone: Signs or symptoms reported by infants or effects on lactation: None. (From Table 6) Potential adverse effects on the fetus: May cross the placenta. No controlled studies have been conducted, but no known teratogenic effects have been identified. Potential side effects on breastfed infants: The active metabolite (canrenone) is excreted into breast milk. FDA Classification: C (C = Laboratory animal studies have shown adverse effects on the fetus (teratogenicity, embryonic lethality, etc.), but there are no controlled studies in pregnant women. Despite the potential risks, the benefits of using this drug in pregnant women may be acceptable, or there are no adequate laboratory animal studies or studies in pregnant women.) /Excerpt from Table II/
For more complete data on drug warnings for spironolactone (17 in total), please visit the HSDB record page.

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Pharmacodynamics
Spionolactone has potassium-sparing diuretic effects. It promotes the excretion of sodium and water and the retention of potassium. It increases renin and aldosterone levels. Spironolactone is a mineralocorticoid receptor antagonist with a low affinity for glucocorticoid receptors. Spironolactone has progesterone and antiandrogenic effects because it binds to androgen receptors and to a lesser extent to estrogen and progesterone receptors. Spironolactone also has anti-inflammatory effects.

C24H32O4S

416.57

416.202

52-01-7

Spironolactone-d7;Spironolactone-d3;Spironolactone-d3-1

5833

White to off-white solid powder

1.2±0.1 g/cm3

597.0±50.0 °C at 760 mmHg

207-208 °C(lit.)

302.3±18.1 °C

0.0±1.7 mmHg at 25°C

1.586

3.12

0

5

2

29

818

7

CC(=O)S[C@@H]1CC2=CC(=O)CC[C@@]2([C@@H]3[C@@H]1[C@@H]4CC[C@]5([C@]4(CC3)C)CCC(=O)O5)C

LXMSZDCAJNLERA-NMFLDQOASA-N

InChI=1S/C24H32O4S/c1-14(25)29-19-13-15-12-16(26)4-8-22(15,2)17-5-9-23(3)18(21(17)19)6-10-24(23)11-7-20(27)28-24/h12,17-19,21H,4-11,13H2,1-3H3/t17-,18-,19+,21+,22-,23-,24-/m0/s1

S-((7R,8R,9S,10R,13S,14S,17S)-10,13-dimethyl-3,5-dioxo-1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16-hexadecahydro-3H-spiro[cyclopenta[a]phenanthrene-17,2-furan]-7-yl) ethanethioate

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.5 mg/mL (6.00 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (6.00 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (6.00 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)