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Questions & Answers
Side Effects & Adverse Reactions
Syncope and "First-dose" Effect: Doxazosin, like other alpha-adrenergic blocking agents, can cause marked hypotension, especially in the upright position, with syncope and other postural symptoms such as dizziness. Marked orthostatic effects are most common with the first dose but can also occur when there is a dosage increase, or if therapy is interrupted for more than a few days. To decrease the likelihood of excessive hypotension and syncope, it is essential that treatment be initiated with the 1 mg dose. The 2, 4, and 8 mg tablets are not for initial therapy. Dosage should then be adjusted slowly (see DOSAGE AND ADMINISTRATION section) with evaluations and increases in dose every two weeks to the recommended dose. Additional antihypertensive agents should be added with caution.
Patients being titrated with doxazosin should be cautioned to avoid situations where injury could result should syncope occur, during both the day and night.
In an early investigational study of the safety and tolerance of increasing daily doses of doxazosin in normotensives beginning at 1 mg/day, only 2 of 6 subjects could tolerate more than 2 mg/day without experiencing symptomatic postural hypotension. In another study of 24 healthy normotensive male subjects receiving initial doses of 2 mg/day of doxazosin, seven (29%) of the subjects experienced symptomatic postural hypotension between 0.5 and 6 hours after the first dose necessitating termination of the study. In this study, 2 of the normotensive subjects experienced syncope. Subsequent trials in hypertensive patients always began doxazosin dosing at 1 mg/day resulting in a 4% incidence of postural side effects at 1 mg/day with no cases of syncope.
In multiple dose clinical trials in hypertension involving over 1500 hypertensive patients with dose titration every one to two weeks, syncope was reported in 0.7% of patients. None of these events occurred at the starting dose of 1 mg and 1.2% (8/664) occurred at 16 mg/day.
In placebo-controlled, clinical trials in BPH, 3 out of 665 patients (0.5%) taking doxazosin reported syncope. Two of the patients were taking 1 mg doxazosin, while one patient was taking 2 mg doxazosin when syncope occurred. In the open-label, long-term extension follow-up of approximately 450 BPH patients, there were 3 reports of syncope (0.7%). One patient was taking 2 mg, one patient was taking 8 mg and one patient was taking 12 mg when syncope occurred. In a clinical pharmacology study, one subject receiving 2 mg experienced syncope.
If syncope occurs, the patient should be placed in a recumbent position and treated supportively as necessary.
Priapism: Rarely (probably less frequently than once in every several thousand patients), alpha1 antagonists, including doxazosin, have been associated with priapism (painful penile erection, sustained for hours and unrelieved by sexual intercourse or masturbation). Because this condition can lead to permanent impotence if not promptly treated, patients must be advised about the seriousness of the condition (see PRECAUTIONS- Information for Patients).
Legal Issues
There is currently no legal information available for this drug.
FDA Safety Alerts
There are currently no FDA safety alerts available for this drug.
Manufacturer Warnings
There is currently no manufacturer warning information available for this drug.
FDA Labeling Changes
There are currently no FDA labeling changes available for this drug.
Uses
A. Benign Prostatic Hyperplasia (BPH). Doxazosin mesylate tablets is indicated for the treatment of both the urinary outflow obstruction and obstructive and irritative symptoms associated with BPH: obstructive symptoms (hesitation, intermittency, dribbling, weak urinary stream, incomplete emptying of the bladder) and irritative symptoms (nocturia, daytime frequency, urgency, burning). Doxazosin mesylate tablets may be used in all BPH patients whether hypertensive or normotensive. In patients with hypertension and BPH, both conditions were effectively treated with doxazosin mesylate tablets monotherapy. Doxazosin mesylate tablets provides rapid improvement in symptoms and urinary flow rate in 66-71% of patients. Sustained improvements with doxazosin mesylate tablets were seen in patients treated for up to 14 weeks in double-blind studies and up to 2 years in open-label studies.
B. Hypertension. Doxazosin mesylate tablets is also indicated for the treatment of hypertension. Doxazosin mesylate tablets may be used alone or in combination with diuretics, beta-adrenergic blocking agents, calcium channel blockers or angiotensin-converting enzyme inhibitors.
History
There is currently no drug history available for this drug.
Other Information
Doxazosin mesylate is a quinazoline compound that is a selective inhibitor of the alpha1 subtype of alpha adrenergic receptors. The chemical name of doxazosin mesylate is 1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(1,4-benzodioxan-2-ylcarbonyl) piperazine methanesulfonate. The empirical formula for doxazosin mesylate is C23H25N5O5 • CH4O3S and the molecular weight is 547.6. It has the following structure:
Doxazosin mesylate is freely soluble in dimethylsulfoxide, soluble in dimethylformamide, slightly soluble in methanol, ethanol, and water (0.8% at 25°C), and very slightly soluble in acetone and methylene chloride. Doxazosin mesylate is available as colored tablets for oral use and contains 1 mg (white), 2 mg (yellow), 4 mg (orange) and 8 mg (green) of doxazosin as the free base.
The inactive ingredients for all tablets are: microcrystalline cellulose, NF; lactose, NF; sodium starch glycolate, NF; magnesium stearate, NF and sodium lauryl sulfate, NF. The 2 mg tablet contains D&C yellow #10 Aluminum Lake and FD&C yellow #6 Aluminum Lake; the 4 mg tablet contains FD&C yellow #6 Aluminum Lake; the 8 mg tablet contains FD&C blue #2 Aluminum Lake and D&C yellow #10 Aluminum Lake.
Sources
Stay Well Manufacturers
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Apotheca Company
![Stay Well (Echinacea Purpurea, Argentum Nitricum, Baptisia Tinctoria, Galium Aparine, Pulsatilla, Thuja Occidentalis, Phosphorus, Thymus Serpyllum, Echinacea, Sulphur,) Liquid [Apotheca Company]](/wp-content/themes/bootstrap/assets/img/loading2.gif)
Stay Well | Remedyrepack Inc.
DOSAGE MUST BE INDIVIDUALIZED. The initial dosage of doxazosin mesylate tablets in patients with hypertension and/or BPH is 1 mg given once daily in the a.m. or p.m. This starting dose is intended to minimize the frequency of postural hypotension and first dose syncope associated with doxazosin mesylate tablets. Postural effects are most likely to occur between 2 and 6 hours after a dose. Therefore blood pressure measurements should be taken during this time period after the first dose and with each increase in dose. If doxazosin mesylate tablets administration is discontinued for several days, therapy should be restarted using the initial dosing regimen.
Concomitant administration of doxazosin mesylate with a PDE-5 inhibitor can result in additive blood pressure lowering effects and symptomatic hypotension; therefore, PDE-5 inhibitor therapy should be initiated at the lowest dose in patients taking doxazosin mesylate tablets.
A. BENIGN PROSTATIC HYPERPLASIA 1-8 mg once daily. The initial dosage of doxazosin mesylate tablets is 1 mg, given once daily in the a.m. or p.m. Depending on the individual patient’s urodynamics and BPH symptomatology, dosage may then be increased to 2 mg and thereafter to 4 mg and 8 mg once daily, the maximum recommended dose for BPH. The recommended titration interval is 1-2 weeks. Blood pressure should be evaluated routinely in these patients.
B. HYPERTENSION 1-16 mg once daily. The initial dosage of doxazosin mesylate tablets is 1 mg given once daily. Depending on the individual patient’s standing blood pressure response (based on measurements taken at 2-6 hours post-dose and 24 hours post-dose), dosage may then be increased to 2 mg and thereafter if necessary to 4 mg, 8 mg and 16 mg to achieve the desired reduction in blood pressure. Increases in dose beyond 4 mg increase the likelihood of excessive postural effects including syncope, postural dizziness/vertigo and postural hypotension. At a titrated dose of 16 mg once daily the frequency of postural effects is about 12% compared to 3% for placebo.
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Alternative Pharmacy
Stay Well | Alternative Pharmacy
10 drops orally, 3 times a day or as directed by a health care professional. Consult a physician for use in children under 12 years of age.
![Stay Well (Argentum Nitricum, Baptisia Tinctoria, Echinacea, Echinacea Purpurea, Galium Aparine, Phosphorus, Pulstilla, Sulphur, Thuma Occidentalis, Thymus Serpyllum) Liquid [Alternative Pharmacy]](http://dailymed.nlm.nih.gov/dailymed/image.cfm?setid=ab533dcb-b628-4db7-a6bb-905de7bf689f&name=ALPH23StayWell1-23-13.jpg)
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