Prazosin: Targeted Alpha-Blockade for Hypertension and PTSD
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Synonyms | |||
Prazosin is a selective alpha-1 adrenergic receptor antagonist, representing a cornerstone in the management of both cardiovascular and certain neuropsychiatric conditions. Its primary mechanism involves the competitive blockade of postsynaptic alpha-1 adrenergic receptors, leading to peripheral vasodilation and a subsequent reduction in blood pressure. Unlike non-selective alpha-blockers, prazosin’s selectivity minimizes the impact on alpha-2 receptors, which are primarily presynaptic and involved in negative feedback mechanisms for norepinephrine release. This specificity contributes to a more favorable side effect profile, particularly a reduced incidence of reflex tachycardia. Its utility has further expanded into the psychiatric domain, where it is employed off-label to mitigate trauma-related nightmares in post-traumatic stress disorder (PTSD), offering a unique neuromodulatory approach.
Features
- Selective alpha-1 adrenergic receptor antagonist
- Available in oral tablet formulations (1mg, 2mg, 5mg)
- Onset of antihypertensive effect occurs within 2 hours
- Peak plasma concentration reached in approximately 1-3 hours
- Elimination half-life of 2-3 hours
- Metabolized primarily in the liver via demethylation and conjugation
- Excreted mainly via bile and feces (>90%), with a minor renal component
Benefits
- Effectively lowers both systolic and diastolic blood pressure through direct arterial and venous vasodilation.
- Reduces peripheral vascular resistance without typically causing a significant reflex tachycardia, a common limitation of direct vasodilators.
- Improves lipid profiles by modestly lowering low-density lipoprotein (LDL) cholesterol and triglycerides while raising high-density lipoprotein (HDL) cholesterol.
- Manages symptoms of benign prostatic hyperplasia (BPH) by relaxing smooth muscle in the bladder neck and prostate.
- Significantly reduces the frequency and intensity of trauma-related nightmares and improves sleep quality in patients with PTSD.
- May be used as part of a combination antihypertensive regimen due to its complementary mechanism of action.
Common use
Prazosin is primarily indicated for the treatment of hypertension, either as monotherapy or, more commonly, in combination with a diuretic or other antihypertensive agents. It is also approved for the symptomatic management of benign prostatic hyperplasia (BPH), alleviating issues such as hesitancy, weak stream, and nocturia. A major and well-established off-label use is for the treatment of nightmare disorder associated with post-traumatic stress disorder (PTSD). It is also sometimes used off-label in the management of Raynaud’s phenomenon and in the treatment of complex regional pain syndrome (CRPS) due to its vasodilatory properties.
Dosage and direction
For Hypertension: The initial dose is 1 mg two or three times daily. The maintenance dose may be slowly increased to a total daily dose of 20 mg given in divided doses. The therapeutic dosage range is typically between 6 mg and 15 mg daily, though some patients may benefit from higher doses. Doses exceeding 20 mg daily usually do not increase efficacy.
For BPH: The usual initial dose is 2 mg twice daily. The dosage may be titrated up to a maximum of 20 mg daily, given in divided doses, based on clinical response and tolerability.
For PTSD-Associated Nightmares (Off-label): Initiation with a very low dose (e.g., 1 mg at bedtime) is critical to minimize the risk of first-dose hypotension. The dose can be gradually titrated upward by 1-2 mg every 5-7 days based on tolerance and therapeutic response. The effective dose range is typically between 3 mg and 15 mg at bedtime, though some individuals may require higher doses.
Administration: The first dose of prazosin, and any substantial subsequent dose increase, should be taken at bedtime to mitigate the risk of syncope. It can be taken with or without food; however, consistent administration with food may slow absorption and reduce peak concentrations, potentially minimizing side effects.
Precautions
The principal precaution associated with prazosin is the potential for first-dose hypotension and syncope, which is a sudden loss of consciousness due to a rapid drop in blood pressure. This is most common after the initial dose or following a rapid increase in dosage. Patients should be warned to avoid situations where injury could result from syncope for the first 12-24 hours after the first dose or a dose increase. Caution is advised in patients with pre-existing renal or hepatic impairment, as metabolism and excretion may be altered, necessitating dose adjustments. Prazosin can cause marked drowsiness and impaired alertness, especially during the initial phase of therapy; patients should be cautioned against driving or operating heavy machinery until they know how the medication affects them. Intraoperative floppy iris syndrome (IFIS) has been observed during cataract surgery in patients on or previously treated with alpha-1 blockers, and surgeons should be informed of the patient’s medication history.
Contraindications
Prazosin is contraindicated in patients with a known hypersensitivity to prazosin or any component of the formulation. Its use is also contraindicated in patients with hypotension (e.g., systolic BP < 100 mmHg). While not an absolute contraindication, extreme caution is required in patients with decompensated heart failure due to the risk of further reducing cardiac preload and afterload.
Possible side effect
Common side effects are often related to its pharmacological action and are usually most pronounced after initiation or dose escalation. These include:
- Dizziness (10.3%)
- Drowsiness (7.6%)
- Headache (7.8%)
- Lack of energy (6.9%)
- Weakness (6.5%)
- Palpitations (5.3%)
- Nausea (4.9%)
- First-dose syncope (1%) Less common side effects include blurred vision, dry mouth, nasal congestion, priapism (a prolonged and painful erection requiring immediate medical attention), and rash.
Drug interaction
Prazosin has several clinically significant interactions:
- Other Antihypertensives (e.g., Diuretics, Beta-blockers, ACE inhibitors, Calcium channel blockers): Concomitant use can lead to an additive hypotensive effect. Careful dosage titration and blood pressure monitoring are essential.
- Phosphodiesterase-5 Inhibitors (e.g., Sildenafil, Tadalafil): These drugs also cause vasodilation and can produce severe, life-threatening hypotension when combined with prazosin. A separation of at least 4 hours is recommended, and combination use is generally avoided.
- CNS Depressants (e.g., Alcohol, Benzodiazepines, Opioids): May potentiate the sedative and hypotensive effects of prazosin.
- Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): May attenuate the antihypertensive effect of prazosin by inhibiting prostaglandin synthesis and causing fluid retention.
- Beta-blockers: While often used together, the combination can increase the risk of first-dose syncope and profound hypotension.
Missed dose
If a dose is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped. The patient should not double the next dose to “make up” for the missed one, as this could precipitate acute hypotension.
Overdose
An overdose of prazosin manifests primarily as an extension of its pharmacological effects: profound hypotension, leading to dizziness, lightheadedness, syncope, and shock. Bradycardia may also occur. Management is primarily supportive and symptomatic. The patient should be placed in a supine position with legs elevated to maximize venous return. Aggressive fluid resuscitation is the first-line treatment for hypotension. If necessary, vasopressor agents (e.g., norepinephrine, phenylephrine) can be administered to support blood pressure. As prazosin is highly protein-bound, dialysis is not likely to be effective.
Storage
Prazosin tablets should be stored at room temperature, between 20°C to 25°C (68°F to 77°F), in a tightly closed container. The medication must be kept out of reach of children and pets. It should be protected from light, excessive moisture, and heat (e.g., not stored in a bathroom cabinet). Do not use tablets that are discolored or show signs of degradation.
Disclaimer
This information is for educational and informational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The author and publisher are not responsible for any errors or omissions or for any outcomes resulting from the use of this information.
Reviews
- Clinical Efficacy (Hypertension): “Prazosin remains a valuable second or third-line agent in our antihypertensive arsenal, particularly in resistant hypertension. Its hemodynamic profile is favorable, and the lipid-neutral/beneficial effects are a plus. The first-dose phenomenon is manageable with proper dosing protocols.” – Cardiologist, 15 years experience
- Psychiatric Application: “The effect of prazosin on PTSD-related nightmares can be transformative for some patients. It’s one of the few pharmacologic options that directly targets the hyperadrenergic state of sleep in PTSD. Titration must be slow and deliberate, but the improvement in sleep architecture and daytime functioning is often remarkable.” – Psychiatrist, specializing in trauma
- Patient Perspective: “After starting prazosin for my blood pressure, I noticed a significant reduction in the terrifying nightmares I’ve had since my service. It’s given me the first restful sleep in years. The dizziness was rough for the first week, but it faded.” – Patient with comorbid HTN and PTSD
- Tolerability: “While effective, the side effect profile, particularly dizziness and orthostasis, can be a significant barrier to adherence, especially in the elderly population. It requires careful patient selection, thorough education, and slow dose escalation.” – Clinical Pharmacist