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Doxazosin: Mechanism, Side Effects and Dosage

Mechanism of Action

Doxazosin is a nonselective α₁-blocker with long elimination half-life. Please see section general pharmacology of alpha blocker.

**Structural formula of doxazosin**

Indications for Doxazosin

Treatment of benign prostatic hyperplasia: Doxazosin improves urinary flow and bladder emptying, relieves irritative and obstructive urinary symptoms (LUTS), reduces the risk of urinary retention, improves the success of a trial without a catheter after urinary retention, and is approved for long-term use.
Treatment of arterial hypertension as a second-line add-on in patients with insufficient effect of the first-line medication.
Off-label treatment of female LUTS due to neurogenic bladder neck obstruction.
Off-label treatment: improve the spontaneous passage of distal ureteral stones.

Pharmacokinetics of Doxazosin

Well absorbed after oral administration, bioavailability 65%, high protein binding, hepatic metabolism (CYP3A4).
Elimination half-life 22 hours, time to steady-state seven days.

Side Effects of Doxazosin

Increased side effect profile since doxazosin is a nonselective α1 blocker.

Hypotension, orthostatic syncope, reflex tachycardia
Stuffy nose
Retrograde ejaculation
Tachyphylaxis in the treatment of hypertension due to volume retention and peripheral edema.
Dizziness, weakness
Rare side effects: priapism (alpha blocker inhibit sympathetic mechanisms for detumescence), intraoperative floppy iris syndrome during cataract surgery.

Contraindications of Doxazosin

Urological Contraindications:

Conservative treatment of BPH with doxazosin is not indicated, if surgical treatment is imperative: chronic urinary retention with renal failure, recurrent hematuria due to prostatic enlargement, recurrent urinary tract infections and bladder stones.

Cardiac Contraindications:

Hypotension, mechanical heart failure (valvular, pulmonary embolism, pericarditis), congestive heart failure.

Other contraindications:

Doxazosin should be paused for cataract surgery to prevent an intraoperative floppy iris syndrome.

Drug interactions

Increased hypotensive effect with other antihypertensives or phosphodiesterase-5 inhibitors.
CYP3A4 inhibitors such as ketoconazole increase the terazosin plasma level and side effects.
Do not combine doxazosin with another alpha blocker for better treatment effect.

Dosage of Doxazosin

The treatment of doxazosin should be started with a low dosage, such as 1 mg orally once daily. The dosage can be increased each week to 2–4–8 mg orally once daily, depending on treatment effect, side effects and blood pressure. Doxazosin should be given before bedtime in the evening to reduce side effects.

Terazosin

Index

Tamsulosin

Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

References

Chapple 2004 CHAPPLE, C. R.: Pharmacological therapy of benign prostatic hyperplasia/lower urinary tract symptoms: an overview for the practising clinician.
In: BJU Int
94 (2004), Nr. 5, S. 738–44

Fusco et al., “Alpha-Blockers Improve Benign Prostatic Obstruction in Men with Lower Urinary Tract Symptoms: A Systematic Review and Meta-analysis of Urodynamic Studies.,” Eur Urol., vol. 69, no. 6, pp. 1091–1101, 2016, doi: 10.1016/j.eururo.2015.12.034.

J. D. McConnell et al., “The long-term effect of doxazosin, finasteride, and combination therapy on the clinical progression of benign prostatic hyperplasia,” N Engl J Med, vol. 349, no. 25, pp. 2387–98, 2003.

C. de Mey, “alpha(1)-blockers for BPH: are there differences?,” Eur Urol, vol. 36 Suppl 3, pp. 52–63, 1999.

Deutsche Version: Doxazosin