α₁-adrenoceptor [3]
Low-density lipoprotein (LDL) receptor (increased binding/number) [2]
Cholesterol synthesis pathway (inhibitory effect) [2]

Long-acting α1-adrenergic receptor inhibitors, such as doxazosin (UK 33274), are frequently used to treat symptoms of lower urinary tract and benign prostatic hyperplasia [1]. Doxazosin may directly suppress the synthesis of cholesterol without the need of LDL receptors. Doxazosin can suppress the synthesis of cholesterol, but cells may counteract this by upregulating LDL receptors. This would increase the import of lipoprotein cholesterol and decrease the amount of LDL cholesterol in the culture medium [2]. In 8 out of 12 patients (66.7%), doxazosin monotherapy was efficacious; in 11 out of 12 patients (91.7%), combination therapy with a beta-blocker was beneficial. Throughout the course of treatment, the average pulse rate did not change. Only three subjects experienced minor and temporary adverse effects. When taking doxazosin, urinary and plasma catecholamine levels usually drop or stay the same [3].

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In Hep G2 cells, Doxazosin at concentrations of 5-20 μmol/L increased LDL binding in a dose-related manner. It also produced dose-related decreases in both newly synthesized cholesterol and cholesterol ester. [2]
In LDL receptor-negative rabbit fibroblasts, which lack functional LDL receptors, Doxazosin (5-20 μmol/L) reduced de novo cholesterol synthesis in a dose-dependent manner (by half at a concentration of 20 μmol/L). However, in LDL receptor-positive rabbit fibroblasts, Doxazosin at the same concentrations had no significant effect on cholesterol synthesis. [2]
Doxazosin had no effect on the level of free cholesterol in Hep G2 cells. [2]
In studies on isolated rabbit and rat heart tissues, (+)-Doxazosin significantly decreased the atrial rate and produced negative inotropic effects, whereas (-)-Doxazosin produced positive inotropic effects in the atria via an α₁-adrenoceptor-independent mechanism. [1]
Both enantiomers of Doxazosin showed no chiral inversion in vitro when a single enantiomer was added to the plasma of rats, dogs, and humans. [1]

In 24 patients with pheochromocytoma, Doxazosin therapy (mean final daily dose 5.10 ± 4.83 mg, range 0.5-16.0 mg) effectively controlled blood pressure. Overall excellent or good antihypertensive efficacy was assessed in 19 of 24 patients (79.2%). Doxazosin monotherapy was effective in 8 of 12 patients (66.7%), and combined therapy with a β-blocker was effective in 11 of 12 patients (91.7%). The mean pulse rate remained constant throughout therapy. Subjective symptoms such as headache, nausea, vomiting, palpitations, and excessive sweating were markedly improved in most patients. [3]
In these patients, urinary and plasma catecholamine (norepinephrine and epinephrine) levels tended to decrease or remained unchanged during Doxazosin therapy while blood pressure was decreased. [3]

The effect of Doxazosin on LDL receptor binding was determined in Hep G2 cells using [¹²⁵I]-LDL. Cells were incubated with varying concentrations of Doxazosin (5-20 μmol/L), and specific binding was measured. To eliminate specific LDL receptor binding, one group of cells was treated with pronase. The results showed that Doxazosin increased [¹²⁵I]-LDL binding in a dose-dependent manner, an effect that was abolished by pronase treatment. [2]
A method using heavy water (D₂O) was developed and validated to determine cholesterol synthesis rates in cell culture. The distribution of deuterium-enriched cholesterol molecules was compared with the theoretical distribution, and no evidence for an important isotope effect was found. Cells were grown in media containing 1% fetal bovine serum (which contains LDL cholesterol) to allow detection of both cholesterol transport and synthesis. After harvesting cells, cholesterol was extracted using the Folch procedure, saponified, and analyzed by isotope ratio mass spectrometry. The proportion of newly synthesized cholesterol was calculated from the relative abundance of the M₀ and M₀₊₆ peaks. [2]
The plasma protein binding of Doxazosin enantiomers was determined using equilibrium dialysis. A dialysis membrane bag containing plasma (rat, dog, or human) was placed in PBS buffer spiked with 200, 400, or 800 ng/mL of (±)-Doxazosin mesylate. After incubation for 15 hours at 37°C, the total concentration (Cₜ) in the bag and the unbound concentration (Cᵤ) in the buffer were measured by chiral HPLC with fluorescence detection (excitation 255 nm, emission 385 nm) using an Ultron ES-OVM column. The bound concentration (C_b) was calculated as C_t - C_u. [1]
To measure catecholamine levels in patients with pheochromocytoma, urinary and plasma samples were collected before and during Doxazosin therapy. The levels of norepinephrine and epinephrine were determined, and it was found that they tended to decrease or remain unchanged during treatment. [3]

Hep G2 cells were used to study LDL receptor binding. Cells were prepared based on the methods of Brown and Goldstein. Pronase was added to one group to eliminate specific LDL receptor binding. The cells were then incubated with [¹²⁵I]-LDL and varying concentrations of Doxazosin (5-20 μmol/L), and binding was measured. [2]
Rabbit fibroblasts (both LDL receptor-positive and LDL receptor-negative from Watanabe rabbits) were used to study cholesterol synthesis. Cells were grown to confluence in media containing 1% fetal bovine serum. Doxazosin, dissolved in dimethylformamide (not exceeding 30 μL per 10 mL of medium), was added to the culture medium at concentrations of 5, 10, and 20 μmol/L for 72 hours. The solvent had no effect on cholesterol synthesis. After incubation, cells were harvested, and cholesterol was extracted. Total cholesterol, free cholesterol, and the percentage of esterified cholesterol were determined by gas-liquid chromatography (GLC). The proportion of newly synthesized cholesterol was determined by isotope ratio mass spectrometry. [2]
In studies on the stereoselective effects of Doxazosin enantiomers, rabbit prostate and rat aorta tissues were used to assess α₁A and α₁D-adrenoceptor activity, respectively. Furthermore, isolated rat and rabbit heart atria were used to evaluate the direct effects of (-)- and (+)-Doxazosin on atrial rate and inotropy. [1]

Absorption, Distribution and Excretion
Doxazosin is rapidly absorbed in the gastrointestinal tract, reaching peak plasma concentrations within 2-3 hours after administration. Bioavailability is approximately 60%-70%. Co-administration of doxazosin with food is not expected to have significant clinical effects.
In a pharmacokinetic study, using a 1 mg intravenous dose of radiolabeled doxazosin and a 2 mg oral dose, 63% of the ingested doxazosin was excreted in feces, and approximately 9% in urine. Trace amounts of the radiolabeled drug were detected in urine, and approximately 5% of the administered dose was excreted unchanged in feces.
The volume of distribution of doxazosin is 1.0-1.9 L/kg. In a study of radiolabeled doxazosin administered to pregnant rats, it was found that doxazosin could cross the placenta.
The clearance of doxazosin is low, approximately 1-2 ml/min/kg.

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Metabolism/Metabolites
Doxazosin is metabolized in the liver to produce inactive O-demethylated and C-hydroxylated metabolites. The metabolic pathway involves O-demethylation of the quinazoline nucleus of doxazosin or hydroxylation of its benzodioxane moiety. Enzymes involved in the metabolism of doxazosin include CYP2C19, CYP2D6, CYP2C19, and CYP3A4, with CYP3A4 being the major metabolic enzyme. Doxazosin itself is considered the main component of its pharmacological action; however, some active metabolites have been identified, but its pharmacokinetics have not been fully characterized.

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Biological Half-Life
According to some sources, the terminal elimination half-life of doxazosin is estimated to be 9–12 hours. The US Food and Drug Administration (FDA) label indicates that the elimination half-life of doxazosin is 22 hours.

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In vitro, the plasma protein binding of Doxazosin enantiomers was found to be high and stereoselective. For (-)-Doxazosin, binding ranged from 89.4% to 94.3% across rat, dog, and human plasma; for (+)-Doxazosin, binding ranged from 90.9% to 95.4%. (+)-Doxazosin exhibited significantly higher protein binding capacity than (-)-Doxazosin in all three species. [1]
The percentage of plasma protein binding differed among species. At concentrations of 400 and 800 ng/mL (±)-Doxazosin, binding in dog plasma was significantly lower than in human plasma. When corrected for total protein concentration (rat: 61.81 mg/mL, dog: 51.35 mg/mL, human: 57.75 mg/mL), the corrected percentage of plasma protein binding was dog > human > rat. [1]
No chiral inversion of Doxazosin enantiomers was observed in vitro after single enantiomer addition to plasma. [1]

Hepatotoxicity

Doxazosin is associated with a low incidence of elevated serum transaminases, which, in controlled trials, was not higher than in the placebo group. These elevations are transient and do not require dose adjustment. No clinically significant acute liver injury caused by doxazosin has been reported in the literature, but the sponsor has received reports of cholestatic hepatitis. Among alpha-adrenergic receptor antagonists, alfuzosin is the most commonly associated with liver injury, while other alpha-blockers have only a few isolated cases with insufficient evidence. Therefore, acute symptomatic liver injury caused by doxazosin is very rare, and severe hepatotoxicity, even if it occurs, is extremely rare.
Probability score: E (Unproven but suspected rare cause of clinically significant liver injury).
Pregnancy and Lactation Effects

◉ Overview of Use During Lactation
Limited information suggests that a daily dose of 4 mg in the mother produces very low drug concentrations in breast milk, and no adverse effects are expected on breastfed infants.
◉ Effects on breastfed infants
No published information found as of the revision date.
◉ Effects on lactation and breast milk
No published information found regarding breastfeeding mothers as of the revision date. However, prazosin, a drug with similar pharmacological effects, does not affect serum prolactin concentrations in hypertensive patients, suggesting that doxazosin may not affect prolactin levels. Prolactin levels in established lactating mothers may not affect their ability to breastfeed.

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Protein binding
The plasma protein binding rate of doxazosin is estimated to be 98%. It has also been shown to bind to α1-acid glycoprotein.

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In a clinical study of 24 patients with pheochromocytoma, adverse reactions to Doxazosin were minor and transient, occurring in only 3 patients (12.5%). These reactions included orthostatic dizziness, abdominal discomfort, and a transient decrease in platelet count (from 20.9×10⁴/mm³ to 9.9×10⁴/mm³, which returned to the normal range of 14.4×10⁴/mm³ on the twenty-seventh postoperative day). No patient withdrew from therapy due to side effects. A statistically significant decrease in hemoglobin (from 13.2±1.7 to 12.6±1.6 g/dL, p<0.05) and lactate dehydrogenase (from 352.2±150.3 to 300.0±108.9 IU/dL, p<0.05) was observed. [3]
Doxazosin and its enantiomers are highly bound to plasma proteins (89.4% to 95.4%) across rats, dogs, and humans, with (+)-Doxazosin showing higher binding than (-)-Doxazosin. [1]

[1]. Stereoselective binding of doxazosin enantiomers to plasma proteins from rats, dogs and humans in vitro. Acta Pharmacol Sin, 2013. 34(12): p. 1568-74.

[2]. D'Eletto, R.D. and N.B. Javitt, Effect of doxazosin on cholesterol synthesis in cell culture. J Cardiovasc Pharmacol, 1989. 13 Suppl 2: p. S1-4; discussion S4.

[3]. Miura, Y. and K. Yoshinaga, Doxazosin: a newly developed, selective alpha 1-inhibitor in the management of patients with pheochromocytoma. Am Heart J, 1988. 116(6 Pt 2): p. 1785-9.

Doxazosin belongs to the quinazoline class of compounds. Its structure is as follows: the quinazoline is substituted at the 4-position with an amino group, at the 6- and 7-positions with a methoxy group, at the 2-position with a piperazine-1-yl group, and at the 4-position with a 2,3-dihydro-1,4-benzodioxin-2-ylcarbonyl group. Doxazosin is an antihypertensive drug used to treat hypertension. It has various pharmacological effects, including antihypertensive, alpha-adrenergic antagonist, antitumor, vasodilatory, and antiproliferative effects. Doxazosin belongs to the quinazoline, N-acylpiperazine, N-arylpiperazine, benzodioxin, monocarboxylic acid amide, and aromatic amine classes of compounds. Doxazosin is an alpha-adrenergic receptor antagonist used to treat symptoms of benign prostatic hyperplasia (BPH) and hypertension. Other members of this class include prazosin, terazosin, tamsulosin, and alfuzosin. Due to its long-lasting effect, doxazosin can be taken once daily. It is marketed by Pfizer and first approved by the U.S. Food and Drug Administration (FDA) in 1990. Doxazosin is an alpha-adrenergic blocker. Its mechanism of action is as an alpha-adrenergic receptor antagonist. Doxazosin is a non-selective alpha-1 adrenergic antagonist (alpha receptor blocker) used to treat hypertension and benign prostatic hyperplasia (BPH). Doxazosin is associated with a low incidence of transient elevations in serum transaminases, but has not been found to be associated with clinically significant cases of acute liver injury. Doxazosin is a quinazoline drug with antihypertensive and antitumor effects. It is an alpha-adrenergic antagonist that selectively inhibits alpha-1 adrenergic receptors. Blocking the action of alpha-1 adrenergic receptors on vascular smooth muscle reduces vascular resistance, thereby exerting an antihypertensive effect. The drug also has a high affinity for alpha-1c adrenergic receptors (the major functional type in the prostate), which may partially explain its efficacy in treating BPH. Furthermore, doxazosin induces apoptosis in prostate cancer cells by inhibiting the death receptor regulation pathway mediated by the protein kinase B (PKB)/Akt signaling pathway. A compound associated with prazosin is a selective α1-adrenergic blocker. See also: doxazosin mesylate (salt form). Drug Indications Doxazosin is indicated for the treatment of symptoms of benign prostatic hyperplasia, including urinary frequency, urgency, and nocturia. It can also be used alone or in combination with various antihypertensive drugs to treat hypertension. Non-indications for doxazosin include the treatment of hypertension in children and ureteral stones. Mechanism of Action Doxazosin selectively inhibits postsynaptic α1 receptors on vascular smooth muscle by non-selectively blocking α1a, α1b, and α1d subtypes. This vascular mechanism reduces systemic peripheral vascular resistance, thereby lowering blood pressure, and has minimal effect on heart rate due to its receptor selectivity. Norepinephrine-activated α1 receptors located in the prostate and bladder neck typically cause local muscle contraction, obstructing urine flow and exacerbating symptoms of benign prostatic hyperplasia (BPH). α1 receptor antagonism can relax the smooth muscle of the prostate and bladder, effectively relieving discomfort symptoms of BPH such as urinary frequency, urgency, and weak urine flow. Recent studies have found that doxazosin can induce apoptosis in hERG potassium channel cells in vitro, which may lead to an increased risk of heart failure with doxazosin use.

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Pharmacodynamics
Doxazosin lowers blood pressure in both standing and lying positions and relieves symptoms of BPH by inhibiting α1 receptors. The pharmacological effects of doxazosin may cause hypotension. This often occurs in the upright position, causing dizziness or lightheadedness. Such reactions may occur with the first dose of doxazosin, but subsequent doses may also cause them. The risk of these reactions is particularly high when the dose is adjusted or when there is a long interval between doses. Treatment should begin with 1 mg of doxazosin and then be slowly titrated to the appropriate dose. Patients must be informed of the risk of fainting and dizziness after taking doxazosin and to avoid such occurrences. It is worth noting that doxazosin is beneficial for blood lipids. It can lower low-density lipoprotein cholesterol (LDL) and triglyceride levels and raise high-density lipoprotein cholesterol (HDL) levels. Regarding the risk of priapism: In rare cases, doxazosin and other alpha-1 receptor blockers may cause priapism, a persistent and unrelieved painful erection that can lead to erectile dysfunction if not treated promptly. Patients must be informed of the risk of priapism associated with taking doxazosin and should seek immediate medical attention if this is suspected.

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(±)-Doxazosin is a long-lasting inhibitor of α₁-adrenoceptors widely used to treat benign prostatic hyperplasia and lower urinary tract symptoms. Its α₁-blocking effects are not limited to the lower urinary tract and also affect vasculature, which can cause vasodilator adverse effects (e.g., dizziness, postural hypotension). A clinical trial (ALLHAT) indicated that its use was associated with a two-fold higher risk of congestive heart failure compared to chlorthalidone among high-risk hypertensive patients. [1]
Doxazosin contains a chiral carbon, creating two enantiomers: (-)-Doxazosin and (+)-Doxazosin. The chiral carbon does not affect therapeutic activity at α₁A-adrenoceptors in the rabbit prostate but significantly affects inhibition of α₁D-adrenoceptors in the rat aorta. [1]
Doxazosin is suggested to have a favorable effect on cholesterol metabolism. The inhibition of cholesterol synthesis may cause cells to upregulate the LDL receptor, increasing the importation of lipoprotein cholesterol and reducing LDL cholesterol in the medium, which supports its beneficial effect on the lipid profile as an antihypertensive agent. [2]
In patients with pheochromocytoma, a clinical prototype of adrenoceptor-mediated hypertension, Doxazosin appears to be an excellent agent for managing hypertension in preoperative or inoperable patients, either alone or in conjunction with a β-blocker. It helps control blood pressure with minimal changes in heart rate and does not seem to increase plasma catecholamine levels. [3]

C23H25N5O5

451.48

451.185

C, 61.19; H, 5.58; N, 15.51; O, 17.72

74191-85-8

Doxazosin mesylate;77883-43-3;Doxazosin-d8 hydrochloride;1219803-95-8;Doxazosin-d8;1126848-44-9

3157

White to off-white solid powder

1.371 g/cm3

718ºC at 760 mmHg

289-290°C

388ºC

2.886

1

9

4

33

678

0

O=C(N1CCN(C2=NC(N)=C3C=C(OC)C(OC)=CC3=N2)CC1)C4OC5=CC=CC=C5OC4

RUZYUOTYCVRMRZ-UHFFFAOYSA-N

InChI=1S/C23H25N5O5/c1-30-18-11-14-15(12-19(18)31-2)25-23(26-21(14)24)28-9-7-27(8-10-28)22(29)20-13-32-16-5-3-4-6-17(16)33-20/h3-6,11-12,20H,7-10,13H2,1-2H3,(H2,24,25,26)

[4-(4-amino-6,7-dimethoxyquinazolin-2-yl)piperazin-1-yl]-(2,3-dihydro-1,4-benzodioxin-3-yl)methanone

UK-33274 mesylateUK33274 mesylateUK 33274 mesylateCardura DoxazosinumDoxazosin Doxazosina Doxazosine Alfamedin Aliud Brand of Doxazosin Mesylate Alpharma Brand of Doxazosin Mesylate Almirall Brand of Doxazosin MesylateAlter Brand of Doxazosin Mesylate Apo Doxazosin Apo-Doxazosin

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)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*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.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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