Prazosin 2mg Capsules
It is used to treat high blood pressure.It may be given to you for other reasons. Talk with the doctor.
Drug Class
Antihypertensive
Pharmacologic Class
Alpha-1 Adrenergic Blocker
Pregnancy Category
Category C
FDA Approved
Jun 1976
DEA Schedule
Not Controlled
Overview
What is this medicine?
Prazosin is a medication used to lower high blood pressure. It works by relaxing blood vessels, allowing blood to flow more easily. It can also be used off-label to help with symptoms of an enlarged prostate or to reduce nightmares in people with PTSD.
How to Use This Medicine
Taking Your Medication
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take your medication as directed, with or without food. Continue taking it even if you feel well, unless your doctor or healthcare provider advises you to stop.
Storing and Disposing of Your Medication
Store your medication at room temperature, protected from light and moisture. Keep it in a dry place, away from the bathroom. Ensure all medications are stored safely and out of reach of children and pets. When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless instructed to do so. Instead, check with your pharmacist for guidance on proper disposal. You may also have access to drug take-back programs in your area.
Missing a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take your medication as directed, with or without food. Continue taking it even if you feel well, unless your doctor or healthcare provider advises you to stop.
Storing and Disposing of Your Medication
Store your medication at room temperature, protected from light and moisture. Keep it in a dry place, away from the bathroom. Ensure all medications are stored safely and out of reach of children and pets. When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless instructed to do so. Instead, check with your pharmacist for guidance on proper disposal. You may also have access to drug take-back programs in your area.
Missing a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
Lifestyle & Tips
- Take the first dose, and any dose increases, at bedtime to minimize dizziness and fainting (first-dose phenomenon).
- Avoid sudden changes in position (e.g., standing up quickly from sitting or lying down) to prevent dizziness or fainting.
- Avoid driving or operating machinery until you know how the medication affects you.
- Limit or avoid alcohol consumption, as it can increase the blood pressure-lowering effects and dizziness.
- Stay well-hydrated, especially in hot weather or during exercise.
- Inform your doctor or dentist that you are taking prazosin before any surgery or dental procedures.
Available Forms & Alternatives
Available Strengths:
Dosing & Administration
Adult Dosing
Standard Dose:
Hypertension: Initially 1 mg orally 2-3 times daily. Maintenance 6-15 mg/day in divided doses.
Dose Range:
1 - 20 mg
Condition-Specific Dosing:
Hypertension:
Initial: 1 mg orally 2-3 times daily. Titrate slowly based on response. Usual maintenance: 6-15 mg/day in divided doses. Max: 20 mg/day.
Benign Prostatic Hyperplasia (Off-label):
Initial: 0.5 mg orally at bedtime. Titrate slowly to 1-2 mg daily.
PTSD-related Nightmares (Off-label):
Initial: 1 mg orally at bedtime. Titrate slowly to 2-10 mg at bedtime.
Pediatric Dosing
Neonatal:
Not established
Infant:
Not established
Child:
Not routinely recommended for hypertension. Limited data for specific off-label uses (e.g., PTSD nightmares) with careful titration.
Adolescent:
Not routinely recommended for hypertension. Limited data for specific off-label uses (e.g., PTSD nightmares) with careful titration.
Dose Adjustments
Renal Impairment:
Mild:
No specific dose adjustment required, but monitor response.
Moderate:
No specific dose adjustment required, but monitor response.
Severe:
No specific dose adjustment required, but monitor response. Initiate with caution and titrate slowly.
Dialysis:
Prazosin is not dialyzable. No specific supplemental dose needed after dialysis. Monitor blood pressure closely.
Hepatic Impairment:
Mild:
No specific dose adjustment required, but monitor response.
Moderate:
Use with caution. Initiate with a lower dose (e.g., 0.5 mg) and titrate slowly due to extensive hepatic metabolism.
Severe:
Use with extreme caution. Initiate with a lower dose (e.g., 0.5 mg) and titrate very slowly. Close monitoring for adverse effects is essential.
Pharmacology
Mechanism of Action
Prazosin is a quinazoline derivative that acts as a selective alpha-1 adrenergic receptor antagonist. It blocks alpha-1 receptors in arterioles and venules, leading to vasodilation and a reduction in peripheral vascular resistance. This results in a decrease in both systolic and diastolic blood pressure. In benign prostatic hyperplasia (BPH), it relaxes smooth muscle in the prostate and bladder neck, improving urine flow.
Pharmacokinetics
Absorption:
Bioavailability:
50-70%
Tmax:
1-3 hours
FoodEffect:
Food may delay absorption but does not significantly affect the extent of absorption.
Distribution:
Vd:
0.5 L/kg
ProteinBinding:
Approximately 95%
CnssPenetration:
Limited
Elimination:
HalfLife:
2-4 hours
Clearance:
Not available
ExcretionRoute:
Primarily bile and feces (6-10% excreted unchanged in urine)
Unchanged:
6-10%
Pharmacodynamics
OnsetOfAction:
Approximately 30-60 minutes
PeakEffect:
2-4 hours
DurationOfAction:
6-10 hours
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Attention Immediately
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical help right away:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Severe dizziness or fainting
Fast or abnormal heartbeat
A painful erection (priapism) or an erection that lasts longer than 4 hours, which can occur even when you are not having sex. If left untreated, this condition may lead to permanent sexual dysfunction.
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other symptoms that bother you or do not go away, contact your doctor or seek medical help:
Feeling dizzy, sleepy, tired, or weak
Headache
* Upset stomach
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical help right away:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Severe dizziness or fainting
Fast or abnormal heartbeat
A painful erection (priapism) or an erection that lasts longer than 4 hours, which can occur even when you are not having sex. If left untreated, this condition may lead to permanent sexual dysfunction.
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other symptoms that bother you or do not go away, contact your doctor or seek medical help:
Feeling dizzy, sleepy, tired, or weak
Headache
* Upset stomach
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Severe dizziness or lightheadedness, especially when standing up
- Fainting (syncope)
- Persistent headache
- Palpitations or rapid heartbeat
- Swelling in ankles or feet
- Shortness of breath
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, any of its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
All medications you are currently taking, including prescription and over-the-counter (OTC) drugs, natural products, and vitamins. This information will help your doctor and pharmacist assess potential interactions between this medication and other substances you are taking.
* Any existing health problems, as this medication may interact with certain conditions or exacerbate underlying health issues.
To ensure your safety, it is crucial to verify that this medication can be taken safely with all your other medications and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, any of its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
All medications you are currently taking, including prescription and over-the-counter (OTC) drugs, natural products, and vitamins. This information will help your doctor and pharmacist assess potential interactions between this medication and other substances you are taking.
* Any existing health problems, as this medication may interact with certain conditions or exacerbate underlying health issues.
To ensure your safety, it is crucial to verify that this medication can be taken safely with all your other medications and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication.
To ensure your safety, avoid driving or engaging in activities that require alertness for 24 hours after taking your first dose, as well as after any dose increase or when restarting the medication after a pause. Before resuming these activities, make sure you understand how this medication affects you.
To minimize the risk of dizziness or fainting, get up slowly from a sitting or lying position, and exercise caution when climbing stairs.
Follow your healthcare provider's instructions for monitoring your blood pressure.
Be aware that this medication may interfere with certain laboratory tests. Inform all your healthcare providers and laboratory personnel that you are taking this medication.
If you are scheduled to undergo cataract surgery or any other eye procedure, consult with your doctor beforehand.
Before using over-the-counter (OTC) products that may increase blood pressure, such as cough or cold medications, diet pills, stimulants, non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen, or certain natural products or aids, discuss their use with your doctor.
Also, talk to your doctor before consuming alcohol. In hot weather or during physical activity, be cautious and drink plenty of fluids to avoid dehydration.
If you are pregnant, plan to become pregnant, or are breastfeeding, inform your doctor. You will need to discuss the potential benefits and risks of this medication for both you and your baby.
To ensure your safety, avoid driving or engaging in activities that require alertness for 24 hours after taking your first dose, as well as after any dose increase or when restarting the medication after a pause. Before resuming these activities, make sure you understand how this medication affects you.
To minimize the risk of dizziness or fainting, get up slowly from a sitting or lying position, and exercise caution when climbing stairs.
Follow your healthcare provider's instructions for monitoring your blood pressure.
Be aware that this medication may interfere with certain laboratory tests. Inform all your healthcare providers and laboratory personnel that you are taking this medication.
If you are scheduled to undergo cataract surgery or any other eye procedure, consult with your doctor beforehand.
Before using over-the-counter (OTC) products that may increase blood pressure, such as cough or cold medications, diet pills, stimulants, non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen, or certain natural products or aids, discuss their use with your doctor.
Also, talk to your doctor before consuming alcohol. In hot weather or during physical activity, be cautious and drink plenty of fluids to avoid dehydration.
If you are pregnant, plan to become pregnant, or are breastfeeding, inform your doctor. You will need to discuss the potential benefits and risks of this medication for both you and your baby.
Overdose Information
Overdose Symptoms:
- Profound hypotension (very low blood pressure)
- Drowsiness
- Bradycardia (slow heart rate)
- Shock
- Loss of consciousness
What to Do:
Seek immediate medical attention. Call 911 or your local emergency number. For poison control, call 1-800-222-1222. Management typically involves supporting blood pressure with intravenous fluids and vasopressors if needed. Keep the patient in a supine position.
Drug Interactions
Major Interactions
- PDE5 Inhibitors (e.g., sildenafil, tadalafil, vardenafil): Risk of symptomatic hypotension.
- Other Alpha-1 Blockers (e.g., tamsulosin, doxazosin): Increased risk of hypotension.
Moderate Interactions
- Beta-blockers (e.g., propranolol, metoprolol): Additive hypotensive effects.
- Diuretics (e.g., hydrochlorothiazide, furosemide): Additive hypotensive effects.
- Calcium Channel Blockers (e.g., amlodipine, verapamil): Additive hypotensive effects.
- NSAIDs (e.g., ibuprofen, naproxen): May reduce the antihypertensive effect of prazosin.
- Alcohol: Enhances hypotensive effects.
Minor Interactions
- Antidepressants (tricyclic, MAOIs): May increase hypotensive effects.
- Antipsychotics: May increase hypotensive effects.
Monitoring
Baseline Monitoring
Blood Pressure (sitting and standing)
Rationale: To establish baseline and assess for orthostatic hypotension before initiating therapy.
Timing: Prior to first dose
Heart Rate
Rationale: To establish baseline.
Timing: Prior to first dose
Routine Monitoring
Blood Pressure (sitting and standing)
Frequency: Regularly, especially during dose titration and periodically thereafter.
Target: Individualized based on treatment goals (e.g., <130/80 mmHg for hypertension)
Action Threshold: Significant orthostatic drop (>20 mmHg systolic or >10 mmHg diastolic) or symptomatic hypotension.
Heart Rate
Frequency: Periodically
Target: 60-100 bpm (normal range)
Action Threshold: Persistent tachycardia or bradycardia outside normal limits.
Symptoms of Orthostatic Hypotension
Frequency: Daily, especially during initial therapy and dose increases.
Target: Absence of dizziness, lightheadedness, syncope.
Action Threshold: Presence of symptoms, particularly 'first-dose phenomenon'.
Symptom Monitoring
- Dizziness
- Lightheadedness
- Fainting (syncope)
- Palpitations
- Headache
- Nausea
- Weakness
Special Patient Groups
Pregnancy
Prazosin is Pregnancy Category C. It should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Animal studies have shown adverse effects, but there are no adequate and well-controlled studies in pregnant women.
Trimester-Specific Risks:
First Trimester:
Potential for fetal harm based on animal data; human data limited.
Second Trimester:
Potential for fetal harm based on animal data; human data limited.
Third Trimester:
Potential for fetal harm based on animal data; human data limited. Risk of neonatal hypotension if used close to delivery.
Lactation
Prazosin is excreted in human milk in small amounts. The American Academy of Pediatrics considers it compatible with breastfeeding. Monitor breastfed infants for signs of hypotension (e.g., lethargy, poor feeding).
Infant Risk:
Low risk. Monitor for drowsiness, poor feeding, or signs of hypotension.
Pediatric Use
Safety and effectiveness have not been established in pediatric patients for hypertension. Use in pediatric populations for off-label indications (e.g., PTSD nightmares) should be done with extreme caution, slow titration, and close monitoring by a specialist.
Geriatric Use
Elderly patients may be more sensitive to the hypotensive effects of prazosin, particularly the 'first-dose phenomenon'. Initiate therapy with a lower dose (e.g., 0.5 mg) and titrate slowly. Monitor blood pressure closely, especially orthostatic changes.
Clinical Information
Clinical Pearls
- The 'first-dose phenomenon' (marked hypotension, dizziness, or syncope) can occur within 30-90 minutes of the initial dose or with rapid dose increases. To mitigate this, administer the first dose and any subsequent dose increases at bedtime.
- Prazosin is often used off-label for benign prostatic hyperplasia (BPH) and PTSD-related nightmares, particularly in veterans.
- Patients should be advised to avoid activities requiring mental alertness for the first few hours after the initial dose or dose increases.
- Tolerance to the hypotensive effect may develop over time, requiring dose adjustments.
- Unlike some other alpha-blockers, prazosin has a relatively short half-life, often requiring multiple daily doses.
Alternative Therapies
- Other Alpha-1 Blockers (e.g., doxazosin, terazosin, tamsulosin, alfuzosin, silodosin)
- Other Antihypertensive Classes (e.g., ACE inhibitors, ARBs, beta-blockers, calcium channel blockers, diuretics)
- For BPH: 5-alpha reductase inhibitors (e.g., finasteride, dutasteride), anticholinergics (e.g., tolterodine), PDE5 inhibitors (e.g., tadalafil)
- For PTSD nightmares: Other antidepressants, antipsychotics (off-label), psychotherapy.
Cost & Coverage
Average Cost:
$10 - $30 per 30 tablets (2mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it's a good idea to check with your pharmacist. If you have any questions or concerns about this medication, don't hesitate to discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide detailed information about the overdose, including the medication taken, the amount, and the time it occurred.