What are the common and serious side effects of doxazosin?

Side Effects of Doxazosin

The primary adverse events of doxazosin include orthostatic hypotension, dizziness, fatigue, ejaculatory dysfunction, and nasal congestion, with the most clinically significant concern being orthostatic hypotension that can precipitate falls and syncope, particularly in elderly patients. 1, 2

Common Side Effects

Cardiovascular Effects

• Orthostatic hypotension and dizziness are the most frequent adverse events, occurring in 15.6% of BPH patients (vs 9% placebo) and 19% of hypertensive patients (vs 9% placebo) 2
• Hypotension occurs in 1.7% of BPH patients (vs 0% placebo) 2
• Palpitations and bradycardia have been reported in post-marketing surveillance 2
• The orthostatic effect is dose-related and more pronounced in the standing position 1, 2

Neurological Effects

• Somnolence affects 3-5% of patients (vs 1% placebo) 2
• Fatigue/malaise is common, occurring in 8% of BPH patients (vs 1.7% placebo) and 12% of hypertensive patients (vs 6% placebo) 2
• Headache and vertigo are reported but less common 2

Genitourinary Effects

• Ejaculatory dysfunction is a recognized adverse event with alpha-blockers, though tamsulosin appears to have higher rates than doxazosin 1
• Polyuria occurs in 2% of hypertensive patients (vs 0% placebo) 2

Respiratory Effects

• Dyspnea affects 2.6% of BPH patients (vs 0.3% placebo) 2
• Rhinitis occurs in 3% of hypertensive patients (vs 1% placebo) 2
• Nasal congestion is a recognized class effect 1

Other Common Effects

• Peripheral edema occurs in 2.7% of BPH patients (vs 0.7% placebo) 2
• Dry mouth affects 1.4% (vs 0.3% placebo) 2

Serious Adverse Events

Congestive Heart Failure Risk

• In men with hypertension and cardiac risk factors, doxazosin monotherapy was associated with higher incidence of congestive heart failure compared to other antihypertensive agents 1
• A Japanese study reported 3 cases of CHF in the doxazosin group vs none in controls, with increased left ventricular diameter observed 3
• Prior use of diuretics may prevent unfavorable effects on left ventricular structure 3
• This risk means alpha-blockers should not be assumed to constitute optimal management of concomitant hypertension 1

Hematologic Effects

• Leukopenia/neutropenia: Decreases in mean WBC and neutrophil counts were observed in controlled trials, though patients remained asymptomatic and counts normalized after discontinuation 2
• Thrombocytopenia has been reported in post-marketing surveillance 2

Intraoperative Floppy Iris Syndrome (IFIS)

• IFIS has been observed during cataract surgery in patients on alpha-1 blockers 2
• This requires ophthalmologic consultation prior to cataract surgery 2

Other Serious Effects

• Priapism has been reported in post-marketing experience 2
• Allergic reactions, including urticaria 2
• Hepatobiliary disorders: cholestasis and cholestatic hepatitis 2
• Bronchospasm (aggravated) 2

Discontinuation Rates

• Overall discontinuation due to adverse events: 6-7% in BPH patients (similar to placebo at 9% and 5% respectively) 4
• In hypertensive patients: 11% with doxazosin vs 4% with placebo 4
• Most common reasons for discontinuation: dizziness, fatigue, headache, and edema 5
• In the ASCOT-BPLA trial, 7.5% discontinued due to adverse events 5

Age-Related Considerations

• Elderly patients (≥65 years) tolerate doxazosin similarly to younger patients, with 42% reporting adverse events vs 47% in younger patients 4
• However, orthostatic hypotension poses greater fall and syncope risk in older adults 6
• Fewer elderly patients had clinically significant blood pressure reductions than younger patients (26% vs 30%) 4

Metabolic Effects

• Small rise in fasting plasma glucose has been observed 5
• Modest favorable effects on lipid profiles (decreased total cholesterol, LDL, triglycerides; increased HDL) 7, 5
• Decreased insulin resistance (HOMA-R reduced by 18.2%) 7

Clinical Pitfalls to Avoid

• Do not assume doxazosin adequately manages concomitant hypertension in patients with cardiac risk factors—separate antihypertensive management may be required 1
• Screen for planned cataract surgery before initiating therapy due to IFIS risk 2
• Monitor for orthostatic symptoms, especially during dose titration and in elderly patients 6
• Consider prior diuretic use in patients at risk for heart failure to prevent adverse left ventricular remodeling 3