Medication Guide App

Minipress Side Effects

Generic Name: prazosin

Note: This page contains information about the side effects of prazosin. Some of the dosage forms included on this document may not apply to the brand name Minipress.

Not all side effects for Minipress may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to prazosin: oral capsule, oral tablet

In addition to its needed effects, some unwanted effects may be caused by prazosin (the active ingredient contained in Minipress). In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking prazosin:

More common
  • Dizziness or lightheadedness, especially when getting up from a lying or sitting position
  • fainting (sudden)
Less common
  • Loss of bladder control
  • pounding heartbeat
  • swelling of the feet or lower legs
Rare
  • Chest pain
  • painful inappropriate erection of penis (continuing)
  • shortness of breath

Some of the side effects that can occur with prazosin may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common
  • Drowsiness
  • headache
  • lack of energy
Less common
  • Dryness of the mouth
  • nervousness
  • unusual tiredness or weakness
Rare
  • Frequent urge to urinate
  • nausea

For Healthcare Professionals

Applies to prazosin: compounding powder, oral capsule

Cardiovascular

Although all patients are susceptible to prazosin-induced postural hypotension, risk factors include higher doses, coadministration of beta-blockers, and preexisting serum sodium depletion.

Animal studies have revealed that prazosin (the active ingredient contained in Minipress) exerts a negative chronotropic action on the sinus node of the dog. Rare evidence of associated bradycardia in man has been reported. A 50-year-old man with benign prostatic hypertrophy developed presyncope, described as "lightheadedness within 45 minutes after taking prazosin". The patient was referred for pacemaker placement. The patient was convinced that the drug was the offending agent, so he stopped it and became asymptomatic. A follow-up electrocardiogram revealed normal sinus rhythm at 55 beats per minute, and the pacemaker placement was cancelled. The author of this case report has located two other such cases that were reported to the United Kingdom Committee on Safety of Medicines over a 30-year period.

Cardiovascular side effects are common during initial therapy. A postural hypotension "first dose effect" has occurred in up to 10% to 70% of patients. For this reason, it is recommended that therapy be started with the patient supine, preferably at bedtime. Syncope has been reported in approximately 1% of patients. Other side effects have included palpitations in 7% to 14% of patients, fluid retention in 5% of patients, and rare case reports of angina and sinus bradycardia. Palpitations may have been due to reflex tachycardia secondary to prazosin-induced decreased peripheral vascular resistance and systemic blood pressure.

Ocular

Ocular side effects including Intraoperative Floppy Iris Syndrome (IFIS) have been observed in some patients undergoing phacoemulsification cataract surgery while being treated with alpha-1 blockers.

Most reports were in patients treated with an alpha-1 blocker at the time IFIS occurred, but in some instances the alpha-1 blocker had been stopped prior to surgery. The manufacturer recommends that patients be questioned to determine whether or not they have taken alpha-1 blockers prior to being considered for cataract surgery. If it is determined that the patient has taken an alpha-1 blocker, the patient's ophthalmologist should be prepared for possible modifications to their surgical technique that may be necessary should IFIS be observed during the procedure.

Nervous system

Hallucinations, irritability, and confusion have been reported in less than 1% of patients. A rare case of hypothermia has been associated with the use of prazosin (the active ingredient contained in Minipress)

Nervous system side effects have included headache in 8% to 18% (more common in patients with a history of migraine), fatigue in 8%, and blurred vision in less than 5% of patients.

Genitourinary

Genitourinary side effects have often been due to alpha-adrenergic blockade of the urinary sphincter muscle.

Genitourinary side effects have included urinary frequency and incontinence. Impotence has been reported in less than 1% of male patients. Priapism has been reported in a few cases, and may be more likely in patients with renal insufficiency.

Gastrointestinal

Gastrointestinal side effects have included nausea in about 5% of patients. Constipation or diarrhea has occurred in less than 4% of patients. Xerostomia has been less common than with less selective alpha-adrenergic receptor blockers.

Rare cases of fecal incontinence, thought to be due to alpha-adrenergic blockade of the anal sphincter due to prazosin, have been reported.

Hypersensitivity

Hypersensitivity reactions have been rare, and have included urticaria and a serum sickness-like reaction manifest as fever, arthralgias, and cold sweats.

Respiratory

Respiratory side effects have been limited to nasal congestion in less than 4% of patients.

Musculoskeletal

Musculoskeletal side effects including rare cases of musculoskeletal complaints and acute febrile polyarthritis have been associated with the use of prazosin (the active ingredient contained in Minipress) The suspected mechanism is immunologic hypersensitivity.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. Drugs.com does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.

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