Introduction
Terazosin Hydrochloride Dihydrate is a long-acting, orally active selective α₁-adrenoceptor antagonist belonging to the quinazoline derivative class, a core oral pharmaceutical raw material for the clinical management of essential hypertension and benign prostatic hyperplasia (BPH). The dihydrate form optimizes the drug’s solubility and stability without affecting its pharmacological activity, and it is chemically stable for pharmaceutical formulation and long-term storage. Its chemical formula is C₁₉H₂₅N₅O₄·HCl·2H₂O, and it is clinically formulated into oral tablets and hard capsules of standard specifications (1 mg, 2 mg, 5 mg, 10 mg) for individualized dose titration. Characterized by high oral bioavailability (~90%), rapid absorption (unaffected by food intake), a long elimination half-life (~12 hours), and dual renal and biliary excretion, it achieves sustained 24-hour therapeutic effects with once-daily administration. As a highly selective α₁-receptor blocker, it has minimal affinity for presynaptic α₂-adrenoceptors, avoiding the disruption of sympathetic neural feedback regulation and reducing the risk of cardiovascular adverse reactions such as reflex tachycardia. It is widely used in cardiology, urology, and geriatrics for the treatment of hypertension (especially in patients with comorbid BPH) and symptomatic BPH, and is a first-line agent for both indications due to its definite efficacy, simple administration, and good tolerability.
Core Pharmacological Mechanism (to support its therapeutic uses)
Terazosin Hydrochloride Dihydrate exerts its therapeutic effects by potently and selectively blocking postsynaptic α₁-adrenoceptors distributed in peripheral vascular smooth muscle and the lower urinary tract (prostate, bladder neck, and urethral sphincter). It has no significant binding affinity for presynaptic α₂-adrenoceptors or other receptors (e.g., β-adrenoceptors, cholinergic receptors), which is the key to its low systemic adverse reaction rate and lack of reflex tachycardia. The drug reversibly competes with norepinephrine for α₁-receptor binding, leading to smooth muscle relaxation and two core therapeutic effects, with equal efficacy for both hypertension and BPH at therapeutic doses:
Antihypertensive effect: By blocking α₁-receptors in peripheral arterial and venous smooth muscle, it dilates both resistance vessels (arterioles) and capacitance vessels (venules), reducing systemic vascular resistance and venous return. This results in a mild, sustained reduction in systolic and diastolic blood pressure, with a gradual onset of action (peak effect at 1–2 hours after administration) that avoids abrupt hypotension. Notably, it has a mild lipid-modulating benefit: it slightly increases plasma high-density lipoprotein (HDL) cholesterol and reduces low-density lipoprotein (LDL) cholesterol and triglycerides, an additional advantage for hypertensive patients with dyslipidemia.
BPH symptomatic relief effect: By blocking α₁-receptors in the prostate stroma, bladder neck, and proximal urethra, it relaxes the smooth muscle of these tissues, reducing bladder outlet obstruction (BOO) and improving the dynamic resistance to urine flow. This directly alleviates the lower urinary tract symptoms (LUTS) of BPH, including obstructive symptoms (difficulty initiating micturition, weak urine stream, incomplete bladder emptying) and irritative symptoms (frequent micturition, urgent micturition, nocturia, urinary frequency). It does not reduce prostate volume but targets the dynamic component of BOO, making it effective for immediate symptomatic relief of BPH.
In terms of pharmacokinetics, the dihydrate moiety is rapidly dissociated after oral administration, and the active terazosin is absorbed into the systemic circulation. The drug is minimally metabolized in the liver (≈40% of the dose is excreted unchanged in urine and bile), with no accumulation in patients with mild to moderate renal or hepatic insufficiency, making it suitable for elderly patients with age-related organ function decline.
Primary Therapeutic Uses
Terazosin Hydrochloride Dihydrate is clinically indicated as a first-line agent for the treatment of essential hypertension in adults and the symptomatic relief of benign prostatic hyperplasia (BPH) in adult males. It is the preferred drug for adult males with concurrent hypertension and BPH, as it simultaneously controls blood pressure and improves urinary symptoms with a single daily dose, avoiding polypharmacy. It is suitable for monotherapy or combination therapy, with proven efficacy in reducing disease-related functional impairment and improving quality of life. Its specific clinical applications are as follows:
1. Essential Hypertension (Adult)
It is a first-line monotherapy for mild to moderate essential hypertension and an effective adjuvant drug for severe/refractory hypertension that cannot be controlled by a single drug. It is particularly suitable for hypertensive populations with special clinical characteristics:
Adult males with hypertension and comorbid BPH (the most common indication for this drug);
Elderly hypertensive patients (≥65 years old), especially those with isolated systolic hypertension (the predominant form of geriatric hypertension), due to its mild, sustained hypotensive effect and low risk of orthostatic hypotension with slow dose titration;
Hypertensive patients with dyslipidemia, benefiting from its mild lipid-modulating effect (elevation of HDL cholesterol);
Hypertensive patients who cannot tolerate other antihypertensive drugs (e.g., ACE inhibitors/ARBs with cough adverse effects, calcium channel blockers with peripheral edema).
It can be combined with all first-line antihypertensive drugs, including thiazide diuretics, ACE inhibitors, ARBs, and dihydropyridine calcium channel blockers, to achieve synergistic hypotensive effects. The combination of terazosin and a thiazide diuretic is a classic regimen for hypertension, as the diuretic counteracts the mild fluid retention that may occur with α₁-receptor blockers, and terazosin offsets the electrolyte disturbance risk of diuretics.
2. Benign Prostatic Hyperplasia (BPH) (Adult Males)
It is a first-line oral agent for the symptomatic treatment of mild to moderate BPH and an adjuvant drug for severe BPH, used to relieve lower urinary tract symptoms (LUTS) and improve urinary flow rate. It is indicated for BPH patients with the following symptoms: obstructive symptoms (difficult urination, weak urine stream, straining to urinate, incomplete emptying) and/or irritative symptoms (frequent micturition, urgent micturition, nocturia ≥2 times, urinary frequency). Key clinical applications include:
Monotherapy for mild to moderate BPH: rapidly relieves LUTS within 1–2 weeks of treatment, improves maximum urinary flow rate (Qmax), and reduces the number of nocturia to improve sleep quality;
Combination therapy for moderate to severe BPH: combined with 5α-reductase inhibitors (e.g., finasteride, dutasteride) for BPH patients with a large prostate volume (>40 mL) or severe BOO. Terazosin provides immediate symptomatic relief (targeting dynamic BOO), while 5α-reductase inhibitors reduce prostate volume (targeting static BOO) over 3–6 months; the combination reduces the risk of acute urinary retention and the need for BPH-related surgery (e.g., transurethral resection of the prostate, TURP) by 50% compared with monotherapy;
Adjuvant treatment for post-BPH surgery: relieves residual LUTS (e.g., frequent micturition, urgent micturition) in patients after TURP or laser prostatectomy, accelerating postoperative urinary function recovery.
Notably, this drug does not reduce prostate volume and is a symptomatic treatment for BPH, not an etiological treatment; it cannot replace surgical intervention for BPH patients with severe complications (e.g., recurrent acute urinary retention, recurrent hematuria, bladder stones, renal insufficiency caused by BOO).
Clinical Application Key Points
Terazosin Hydrochloride Dihydrate requires slow dose titration to minimize the risk of first-dose hypotension (a characteristic adverse effect of α₁-receptor blockers), and its clinical use follows the principle of individualized dosing based on indication, age, and patient tolerability. Key application points for administration, safety, and drug compatibility are as follows:
1. Administration and Dosage
Oral administration, once daily, can be taken with or without food (food has no effect on absorption or efficacy); tablets/capsules are swallowed whole with water. The core principle is low initial dose + bedtime administration + gradual titration to avoid first-dose hypotension and orthostatic hypotension. Dosing is differentiated by indication, with no dose adjustment required for mild to moderate renal insufficiency (eGFR ≥30 mL/min/1.73m²):
Essential Hypertension: Initial dose = 1 mg at bedtime (first dose); titrate the dose every 7–14 days according to blood pressure control (2 mg → 5 mg → 10 mg once daily); the maintenance dose is 1–10 mg/day, and the maximum daily dose is 20 mg (higher doses do not increase hypotensive efficacy but may increase adverse reactions);
Benign Prostatic Hyperplasia (BPH): Initial dose = 1 mg at bedtime (first dose); titrate the dose to 2 mg once daily after 7 days, then to 5 mg once daily, and adjust to 10 mg once daily if symptoms are not relieved; the maintenance dose is 2–10 mg/day, and the maximum daily dose is 20 mg;
Hypertension + BPH (comorbidity): Follow the BPH dosing regimen, which simultaneously achieves effective blood pressure control and BPH symptom relief;
Elderly patients (≥65 years old): Regardless of indication, the initial dose is 1 mg at bedtime, and the titration interval is extended to 14 days to adapt to blood pressure and urinary symptom changes.
For patients with severe hepatic insufficiency (Child-Pugh C grade), the dose is reduced by 50%, and blood pressure/urinary symptoms are closely monitored due to reduced hepatic metabolism and excretion.
2. Main Adverse Reactions
Adverse reactions are mild, transient, and dose-related, mostly appearing in the first 1–2 weeks of treatment (initial titration phase) and resolving spontaneously with continued administration or dose reduction; the overall incidence is <15%, and severe adverse reactions are extremely rare. Adverse reactions are mainly related to α₁-receptor blockade, with no organ toxic effects:
Most common (incidence 5–15%): First-dose hypotension (dizziness, vertigo, lightheadedness), orthostatic hypotension (dizziness upon standing), headache, fatigue, drowsiness, nasal congestion (vascular dilation of nasal mucosa), and mild peripheral edema (fluid retention); these are the main adverse reactions of α₁-receptor blockers and are significantly reduced by bedtime administration and slow titration;
Less common (incidence 1–5%): Mild gastrointestinal symptoms (nausea, diarrhea, abdominal discomfort), dry mouth, blurred vision (transient), palpitations (rare, no reflex tachycardia), and ejaculatory dysfunction (retrograde ejaculation, reduced ejaculate volume—rare in BPH patients, reversible after drug withdrawal);
Rare severe adverse reactions (incidence <1%): Syncope (caused by severe first-dose hypotension in non-compliant patients), severe allergic reactions (rash, urticaria, angioedema), and abnormal liver function (transient elevation of transaminases, reversible after withdrawal).
Long-term use (≥12 months) has no cumulative adverse effects on the heart, liver, kidney, or reproductive system, making it suitable for chronic long-term treatment of hypertension and BPH.
3. Contraindications
Terazosin Hydrochloride Dihydrate is contraindicated in patients with:
Hypersensitivity to terazosin hydrochloride dihydrate, other quinazoline-derived α₁-adrenoceptor blockers (e.g., doxazosin, prazosin), or any component of the pharmaceutical preparation;
Severe hypotension (systolic blood pressure <90 mmHg) or orthostatic hypotension;
Acute urinary retention caused by BPH (initial bladder catheterization is required to relieve retention before drug initiation);
Severe aortic or mitral valve stenosis (risk of exacerbating hypotension due to reduced cardiac output).
4. Key Precautions
First-dose effect prevention: Strictly administer the first 1 mg dose at bedtime; avoid strenuous activity or sudden postural changes (standing up quickly) within 8–12 hours after the first dose to prevent syncope or severe dizziness;
Orthostatic hypotension warning: Instruct patients to change posture slowly (lie down → sit up → stand up, with a 1–2 minute pause at each step), especially in the morning (the peak time for orthostatic hypotension); if dizziness/vertigo occurs, immediately lie down until symptoms resolve;
Driving and operating machinery: Mild drowsiness, dizziness, or blurred vision may occur in the initial titration phase; avoid engaging in high-risk activities (driving, operating heavy machinery) until the body adapts to the drug (usually 2–4 weeks);
Hepatic/renal insufficiency: No dose adjustment for mild to moderate renal insufficiency (the drug is excreted by both kidneys and bile); severe hepatic insufficiency requires dose reduction and close monitoring; severe renal insufficiency (eGFR <30 mL/min/1.73m²) requires regular monitoring of serum drug concentrations;
Pregnancy and lactation: Not recommended for use in pregnant or lactating women. The drug is indicated for adult males (BPH) and adult hypertension (no clinical safety data for fetal/infant exposure); if used in hypertensive pregnant women, the therapeutic benefit must outweigh the potential fetal risk; breastfeeding is prohibited during treatment (the drug is excreted in breast milk);
Surgical anesthesia: Inform the anesthesiologist of terazosin use before any surgery (including minor surgery), as α₁-receptor blockade may enhance the hypotensive effect of general anesthetics and increase the risk of intraoperative hypotension; temporary drug discontinuation 24–48 hours before surgery is recommended for high-risk surgery;
BPH patient monitoring: For BPH patients, if LUTS worsen (e.g., acute urinary retention, severe dysuria) or new symptoms occur (hematuria, flank pain) during treatment, immediately discontinue the drug and perform urological examinations to rule out severe BPH complications or other urinary tract diseases;
Abrupt withdrawal: No severe withdrawal symptoms; gradual dose reduction over 1–2 weeks is recommended for long-term users to avoid transient rebound hypertension (rare) or BPH symptom worsening.
5. Drug Interactions
Terazosin Hydrochloride Dihydrate has a low risk of clinically significant drug interactions due to its selective α₁-receptor blockade and minimal hepatic metabolism (no induction/inhibition of cytochrome P450 enzymes). Most drug interactions are synergistic hypotensive effects with other cardiovascular drugs, and minor adjustments to the dosing regimen are sufficient to manage risks. Key drug interactions are as follows:
Antihypertensive drugs: Combined use with thiazide diuretics, ACE inhibitors, ARBs, calcium channel blockers, nitrates, or beta-blockers produces a synergistic hypotensive effect; the dose of each drug should be reduced by 30–50% when combined to avoid severe hypotension;
Nonsteroidal anti-inflammatory drugs (NSAIDs): NSAIDs (e.g., ibuprofen, naproxen) may slightly weaken the hypotensive effect of terazosin by causing sodium and water retention; monitor blood pressure when combined, and increase the terazosin dose if necessary (no effect on BPH efficacy);
Vasodilators/nitrates: Combined use with nitroglycerin, isosorbide dinitrate, or other vasodilators enhances peripheral vasodilation and increases the risk of hypotension; avoid combined use in patients with severe hypertension or BPH with cardiovascular disease;
Sympathomimetic drugs: Epinephrine, norepinephrine, or other sympathomimetic drugs may antagonize the α₁-blocking effect of terazosin and cause rebound hypertension; avoid combined use unless necessary for emergency treatment;
Cimetidine: Cimetidine slightly inhibits the hepatic metabolism of terazosin, increasing plasma drug concentrations by ≈20% (no clinical significance); no dose adjustment is required for routine combination use;
Oral anticoagulants/lipid-lowering drugs: No significant interaction with warfarin, statins (atorvastatin, rosuvastatin), or fibrates; safe for combination use in hypertensive/BPH patients with dyslipidemia or atrial fibrillation;
Antidiabetic drugs: No interference with the efficacy of oral hypoglycemic agents or insulin; safe for combination use in hypertensive/BPH patients with type 2 diabetes;
Over-the-counter (OTC) drugs: No interaction with antipyretics (acetaminophen), antihistamines, or cough/cold preparations; avoid OTC drugs containing pseudoephedrine (a sympathomimetic) to prevent rebound hypertension.
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