Doxazosin (oral)

Available since 1990 for the treatment of hypertension and benign prostatic hyperplasia, doxazosin mesylate is a quinazoline compound that may be used alone or in combination with other medications to control blood pressure.

Overview

Doxazosin is a member of the family of medications known as alpha blockers. It is marketed under the names Cardura, Cardura XL, Carduron and Doxadura. It is used primarily as a treatment for high blood pressure and is also used to mitigate the symptoms of benign prostatic hyperplasia (an enlarged prostate). It does not reduce the size of the prostate or cure the condition, but it relaxes the muscles in the neck of the bladder and prostate making it easier for men suffering from this condition to urinate and reducing the frequency of the need to urinate.

Doxazosin was approved by the FDA for both of these uses in 1990. There is some evidence from studies conducted in 2000 that alpha blockers as a class are less effective in the prevention of cardiovascular diseases that result from hypertension than other classes of medications used for similar purposes, including simple diuretics. However, these medications continue to be available as a treatment for high blood pressure.

Alpha-adrenergic blockers function by binding to alpha-adrenoceptors on vascular smooth muscles. These adrenoceptors stimulate the sympathetic nerves in blood vessels. By antagonizing and blocking these receptors, the blood vessels are relaxed which lowers blood pressure. Doxazosin also targets receptors that impact the muscles of the bladder and prostate, which is how this medication can reduce the symptoms of an enlarged prostate.

Doxazosin is generally very well tolerated with few side effects and low risk. The most common side effect experienced by patients is dizziness and lightheadedness associated with sudden drops in blood pressure. It typically occurs as the patient initially begins treatment, dosing levels are adjusted and increased or the patient restarts the medication after discontinuing its use for a period of time. The risk associated with low blood pressure is the danger of sudden fainting, loss of balance and possible injury that may occur from falling. This symptom will generally diminish with continued use as the patient adjusts to the medication. It can cause an allergic reaction which can be serious, but hypersensitivity to doxazosin is rare. It can also cause digestive issues and headaches.

There has not been extensive testing or research into the efficacy and safety of doxazosin in pediatric patients or pregnant women. It is not recommended for patients under the age of eighteen. In regard to pregnant women, physicians and patients must consider the risks associated with the medication versus the risks of high blood pressure during pregnancy (e.g. preterm labor, preeclampsia) to determine the best course of treatment. There is some evidence that suggests nursing mothers may pass the medication through breast milk to the infant, so doxazosin is not recommended unless the risks of hypertension to the mother are estimated to be greater.

Doxazosin is delivered in tablet form at various strengths. It is taken orally once a day, with or without food with a dosage level between 1mg and 16mg daily. It should be stored at room temperature away from direct sunlight and moisture, and kept in its original container in a safe, secure location. There is a danger of accidental overdose with this medication so it should be kept away from children and pets. Unused medication should not be flushed down the toilet or disposed of in regular household trash.

Conditions Treated

  • Hypertension
  • Benign prostatic hyperplasia (BPH)

Type Of Medicine

  • Alpha-adrenergic blocker, a compound of quinazoline

Side Effects

Doxazosin is generally well tolerated by most patients. However, as with any effective medication, it does have known side effects. Many of these side effects, while inconvenient or uncomfortable, do not require medical attention. These symptoms include:

  • Exhaustion
  • Perceived weakness
  • Headache

The above list of side effects are not particularly dangerous and occur commonly. The following are not necessarily dangerous but are less common:

  • Heartburn
  • Urine that is cloudy
  • Urinary tract infection
  • Stiffness of joints or muscles
  • Upset or sour stomach
  • Frequent belching
  • Increased and more frequent urination
  • Indigestion
  • Painful urination
  • Pain in the lower back
  • Pain in the joints
  • Cramping in muscles
  • Pain in the side
  • Increased drowsiness
  • Sore throat
  • Swollen joints
  • Runny nose

Many of these side effects will go away after a few weeks of taking doxazosin. If these side effects persist and are of concern to the patient, he or she should share this information with their physician at a regular appointment.

Some side effects caused by doxazosin are more significant and should be discussed with a physician as soon as possible as other medical treatment may be necessary, including discontinuing use of doxazosin. These side effects include:

  • Syncope (sudden fainting)
  • Increased heartbeat
  • Dizziness
  • Disorientation or confusion
  • Blurry vision
  • Lightheadedness, particularly when moving from lying down or sitting
  • Pounding heartbeat
  • Excessive or unusual sweating
  • Edema of the ankles or feet
  • Shortness of breath
  • Arrhythmia of heartbeat

Very rarely, doxazosin has been reported to cause prolonged erections, a condition called priapism. If this situation occurs, it requires immediate medical attention. Men suffering from priapism should go to an emergency room immediately.

Other side effects that have been reported, but are very rare include:

  • Blood in urine
  • Rash in various regions of the body
  • Black or clay colored stool
  • Fever or chills
  • Feeling of tightness in the chest or chest pain
  • Blood in the stool
  • Persistent cough
  • Abnormally dark urine
  • Increased anxiety levels
  • Idiopathic itching
  • Gout
  • Difficulty breathing
  • Sudden, severe headache
  • Diarrhea
  • Chronic fatigue
  • Decreased liver function
  • Decreased appetite
  • Jaw pain
  • Canker sores inside the mouth or on the lips
  • Difficulty speaking or slurred speaking
  • Convulsions or seizures
  • Halitosis
  • Unusual swollen glands
  • Neck pain
  • Bruising easily
  • Sudden loss of vision
  • Unusual bleeding
  • Vomiting with or without blood
  • Yellowing of eyes
  • Sudden weakness in arm or leg
  • Weight loss
  • Loss of hair/ thinning of hair
  • Trouble holding urine
  • Gynecomastia in men

These symptoms should be shared with the patient's medical care provider as soon as possible.

It is possible for a patient to experience an allergic reaction or hypersensitivity to doxazosin. This response may include hives, wheezing, swelling of the throat, eyes, mouth or face, and/or difficulty breathing. If an allergic reaction is suspected, the patient should seek medical attention immediately.

Dosage

For the treatment of benign prostatic hyperplasia (BPH), there are two options of doxazosin available in either Cardura (immediate release) or Cardura XL (extended release). For Cardura immediate release, the initial dosing level is 1mg once a day, in the morning or the evening. Dosage should be adjusted at the end of one or two weeks, with a maintenance dose somewhere between 1mg and 8mg taken once daily.

When using Cardura XL, the beginning dose is 4mg a day taken in the morning with breakfast. The dosage level may adjust after three to four weeks to a maximum level of 8mg taken once a day. Cardura XL should only be prescribed for the treatment of BPH. It is not indicated for the treatment of hypertension.

When taking doxazosin for treatment of hypertension, the beginning dose is 1mg taken daily. After a week, the dosage may be adjusted up, and may continue to be adjusted gradually over a period of weeks to a maximum dosage of 16mg once a day to reach the desired reduction of blood pressure.

For patients with mild liver impairment, the dosage level may need to be reduced and the patient's liver function should be monitored. For patients with severe hepatic impairment, doxazosin is contraindicated.

There is no information regarding altered dosages for patients suffering from renal impairment or those who are on dialysis.

Doxazosin is not recommended for patients under the age of eighteen or patients who suffer from hypotension.

Dosage levels for geriatric patients may need to be reduced somewhat depending on the significance of the side effects they experience.

Interactions

Doxazosin mesylate (Cardura) interacts with many families of medicines, a variety of conditions and alcohol use. The drug interactions include a total of 437 drugs, both generic and brand name. The most significant interactions include the following medications:

  • Tizanidine
  • Allergen extract, ragweed pollen
  • Boceprevir
  • Allergen extract, mixed grass
  • Sodium oxybate
  • Allergen extract, timothy grass pollen

Doxazosin has a more moderate interaction with many other medications. Use of Cardura is not necessarily contraindicated with these medications, but physicians should use caution and monitor combined use carefully. These medications include:

  • Amitryptyline
  • Acetaminophen
  • Hydrocodone
  • Codeine
  • Apomorphine
  • Ephedrine
  • Apraclonidine ophthalmic
  • Secobarbital
  • Phenobarbital
  • Guaifenesin
  • Dextromethorphan
  • Olmesartan
  • Aspirin
  • Aripiprazole
  • Amyl nitrate
  • Alfuzosin
  • Acetylcarbromal
  • Atenolol
  • Aliskiren
  • Asenapine
  • Aldesleukin
  • Ammonium chloride
  • Oxycodone
  • Hydrochlorothiazide
  • Avanafil
  • Baclofen
  • Lidocaine (topical)
  • Budesonide
  • Betaxolol
  • Brompheniramine
  • Belladonna
  • Opium
  • Formoterol
  • Benzthiazide
  • Fentanyl
  • Phenylephrine
  • Bisoprolol
  • Bupropion
  • Timolol ophthalmic
  • Hyoscyamine
  • Brimonidine, topical or ophthalmic
  • Naloxone
  • Sufentanil
  • Bupivacaine
  • Cortisone
  • Chloral hydrate
  • Methyldopa
  • Pseudoephedrine
  • Sodium citrate
  • Chlordiazepoxide
  • Methscopolamine
  • Clidinium
  • Carvedilol
  • Clozapine
  • Carbinoximine
  • Cariprazine
  • Clobazam
  • Chlorcyclizine
  • Clomipramine
  • Carteolol
  • Cosyntropin
  • Pyrilamin
  • Triprolidine
  • Conjugated estrogens
  • Droperidol
  • Diazepam
  • Dapagliflozin
  • Metformin
  • Ibuprofen
  • Doxepin
  • Dezocine
  • Dutasteride
  • Dexmedetomidine
  • Deflazacort
  • Magnesium salicylate
  • Tamsulosin
  • Dyphylline
  • Empagliflozin
  • Felodipine
  • Ethanol
  • Epoprostanol
  • Enalapril
  • Estazolam
  • Theophylline
  • Fludrocortisone
  • Flurazepam
  • Fenoldopam
  • Fluoxetine
  • Furazolidone
  • Fluphenazine
  • Heroin
  • Valsartan
  • Haloperidol
  • Hydroxyzine
  • Reserpine
  • Hydralazine
  • Halazepam
  • Hydrocortisone
  • Spironolactone
  • Moexipril
  • Losartan
  • Triamterene
  • Isocarboxazid
  • Iloperidone
  • Indapamide
  • Iloprost
  • Levodopa
  • Lurasidone
  • Labetalol
  • Lithium
  • Licorice
  • Loxapine
  • Levobunolol ophthalmic
  • Linezolid
  • Naltrexone
  • Methadone
  • Maraviroc
  • Methylprednisone
  • Methdilazine
  • Minoxidil (topical)
  • Methocarbamol
  • Midodrine
  • Morphine
  • Nadolol
  • Nortriptyline
  • Nalbuphine
  • Nifedipine
  • Nebivolol
  • Olanzapine
  • Orphenadrine
  • Olopatadine nasal
  • Propanolol
  • Prednisolone
  • Pentoxifylline
  • Paliperidone
  • Prochlorperazine
  • Paraldehyde
  • Polythiazide
  • Phenalzine
  • Propiomazine
  • Perindopril
  • Quetiapine
  • Quazepam
  • Quinapril
  • Riociguat
  • Ramipril
  • Reserpine
  • Rasagiline
  • Sodium thiosulfate
  • Selexipag
  • Silodosin
  • Safinamide
  • Sildenafil
  • Triazolam
  • Thalidomide
  • Treprostinil
  • Thiothixene
  • Trazodone
  • Temazepam
  • Tranylcypromine
  • Thiethylperazine
  • Verteporfin
  • Vardenafil
  • Ziprasidone
  • Zaleplon
  • Zolpidem

Patients taking Cardura or any other version of doxazosin should avoid alcohol or use very sparingly. Alcohol can cause increased dizziness, warmth and flushing of the skin when ingested in conjunction with doxazosin. This is especially true for patients of Asian descent.

Patients with hypotension or low blood pressure who are prescribed doxazosin to treat benign prostatic hyperplasia should take this medication with caution and medical supervision. While doxazosin can mitigate some of the symptoms of BPH, it will also lower the blood pressure of the patient even further, which can cause increased dizziness, fainting, irregular heartbeat and other side effects linked to hypotension.

Doxazosin may exacerbate lowered white blood cell counts in patients who also suffer from depressed bone marrow production or neutropenia. Frequent monitoring of white blood cell counts for these patients is indicated when prescribed doxazosin.

Because doxazosin is primarily metabolized in the liver, patients with hepatic impairment and reduced liver function should be prescribed this medication with caution. The effects of doxazosin are increased and so a reduced dosage is generally indicated but may need to be adjusted depending on how well the patient tolerates the medication and metabolizes it.

Warnings

Patients who have a known hypersensitivity to any of the components of doxazosin mesylate or other quinazoline based medications should not be prescribed this medication.

Cardura XL, the extended release formula, is only indicated for the treatment of benign prostatic hyperplasia (BPH). It should not be prescribed as a treatment for hypertension.

For patients taking doxazosin who also require cataract surgery, there is an increased risk of a condition called Intraoperative Floppy Iris Syndrome, which may complicate the procedure. These patients should be sure to inform their surgeon that they are on a regimen including doxazosin so that it can be factored into the surgical planning. There is no evidence that discontinuation of doxazosin prior to the cataract surgery reduces this risk.

Men prescribed doxazosin should be advised on the risks of priapism, and the need to seek immediate medical treatment should this condition arise. Left untreated, prolonged and painful erections may lead to impotence.

There is some risk of liver damage when taking doxazosin. This risk is greatest in patients who already have compromised liver function. Frequent testing of liver function should be part of the monitoring process for these patients.

Doxazosin has not been shown to cause cancer; however, BPH and cancer of the prostate have similar symptoms and may coexist. Careful screening to insure the patient does not have prostate cancer is indicated before using doxazosin to treat BPH.

The most common risk associated with doxazosin is the dizziness and lightheadedness associated with low blood pressure. The risk is greatest at the initial stages of use. Careful supervision and monitoring of the patient's blood pressure can help mitigate some of that risk.

There has not been sufficient research in the use of doxazosin in pregnant women to determine the risk it might present. However, hypertension in pregnant women can cause many complications including increased risk of gestational diabetes, preeclampsia, early labor and intrauterine death of the fetus. Therefore, physicians should weigh the risks of high blood pressure against the possible risks of the use of doxazosin when determining the course of treatment for the mother.

There is some indication that very low levels of doxazosin are excreted through breast milk. Nursing mothers should take this medication with some caution.

Overdose of doxazosin is possible and dangerous as it leads to very low blood pressure. The typical protocol for suspected overdose of this medication is gastric lavage and fluid therapy.

Doxazosin has not been studied for use with pediatric patients and is not recommended. Geriatric patients may require adjusted dosing levels.

Storage

Doxazosin mesylate is marketed under the names Cardura, Carduran, Doxadura, Cardura XL and Cascor. It is delivered in four different strengths: 1mg, 2mg, 4mg, and 8mg. The 1mg drug is delivered as a white round tablet. The other strengths are white, capsule shaped tablets. All forms of this medication are taken orally.

All strengths of this drug are sold in bottles of 100 tablets or in cartons of blister packs with a total of 100 tablets.

The medication should be sealed tightly in its original container until use. It should be stored at room temperature (between 60 to 77 degrees Fahrenheit or 20 to 25 degrees Celsius). It should be kept away from excessive light, heat or moisture to ensure efficacy. It is possible to overdose on this medication, so it should be kept safely stored out of the reach of children or pets.

Summary

Doxazosin is an alpha-adrenergic blocker that has proven effective in the treatment of hypertension and benign prostatic hyperplasia. Alpha blockers function through intercepting the receptors that stimulate the nerves that constrict blood vessels. This antagonism helps blood vessels relax, lowering blood pressure in those vessels. Doxazosin does not actually reduce the size of the prostate in treating BPH, but it does relax the muscles in the bladder neck and around the prostate, addressing difficulty and frequency of urination in men with this condition.

This drug has been available since 1990, and is considered effective and safe for most patients. There are some common side effects, including dizziness, stomach upset and headaches, but these symptoms tend to diminish over time as the patient adjusts to the medication. It is typically well tolerated.

Dosing levels vary from 1mg to 16mg daily. Overdose is possible with the danger being a rapid and significant drop in blood pressure. For patients with hepatic impairment, dosing levels may need to be reduced. Doxazosin is metabolized for the most part in the liver and can impact liver function. If a patient has severe liver impairment, this medication is contraindicated. It is also not recommended for patients under the age of 18. Patients with BPH who also have low blood pressure may not be good candidates for doxazosin treatment either as this medication will further reduce blood pressure levels and may exacerbate those symptoms associated with hypotension. Any patient prescribed doxazosin (Cardura, etc.) should take this medication as part of an overall treatment plan that includes monitoring of blood pressure, liver function and white blood cell counts and regular consultations with a physician.