What are the side effects of doxazosin?

Side Effects of Doxazosin

Doxazosin causes orthostatic hypotension, dizziness, fatigue, and ejaculatory dysfunction, with a notably higher risk of congestive heart failure in men with cardiac risk factors compared to other antihypertensives. 1, 2

Most Common Adverse Effects

Cardiovascular Effects

• Orthostatic hypotension is the primary cardiovascular concern, occurring in 1.7% of BPH patients (vs 0% placebo) and manifesting as blood pressure drops when changing positions 2
• Doxazosin demonstrates a higher probability of orthostatic hypotension compared to tamsulosin, making it less safe for older adults vulnerable to falls 3
• Peripheral edema occurs in 2.7% of BPH patients (vs 0.7% placebo), likely due to expansion of extracellular fluid volume 1, 2
• Congestive heart failure risk is significantly elevated in men with hypertension and cardiac risk factors based on the ALLHAT study, making doxazosin contraindicated in this population 3, 1

Neurological Effects

• Dizziness/vertigo is the most frequent adverse effect, occurring in 15.6% of BPH patients (vs 9% placebo) and 19% of hypertensive patients (vs 9% placebo) 2
• Somnolence occurs in 3.0% of BPH patients (vs 1.0% placebo) and 5% of hypertensive patients (vs 1% placebo) 2
• Fatigue/asthenia affects 8.0% of BPH patients (vs 1.7% placebo) and 12% of hypertensive patients (vs 6% placebo), which can contribute to weight gain by altering energy balance 1, 2

Respiratory Effects

• Dyspnea occurs in 2.6% of BPH patients (vs 0.3% placebo) 2
• Nasal congestion/rhinitis affects 3% of hypertensive patients (vs 1% placebo) due to alpha-receptor blockade in nasal vasculature 2

Genitourinary Effects

• Ejaculatory dysfunction is a recognized adverse effect, though the FDA label does not quantify the specific incidence rate 1, 2
• Polyuria occurs in 2% of hypertensive patients (vs 0% placebo) 2

Other Common Effects

• Dry mouth affects 1.4% of BPH patients (vs 0.3% placebo) 2
• Headache is frequently reported across multiple studies 4, 5

Serious Adverse Effects

Hematologic Effects

• Leukopenia/neutropenia with decreases in mean white blood cell and neutrophil counts observed in controlled trials, though counts returned to normal after discontinuation and no patients became symptomatic 2
• Post-marketing reports include thrombocytopenia 2

Ophthalmologic Effects

• Intraoperative Floppy Iris Syndrome (IFIS) has been reported in post-marketing surveillance, complicating cataract and glaucoma surgery 2

Rare Post-Marketing Effects

• Priapism (prolonged painful erection requiring emergency intervention) 2
• Cholestatic hepatitis and cholestasis 2
• Bronchospasm (aggravated) 2
• Bradycardia 2
• Allergic reactions including urticaria 2

Age-Related Considerations

• Elderly patients (≥65 years) tolerate doxazosin similarly to younger patients, with 42% of elderly normotensive patients reporting adverse events vs 47% in younger patients 6
• However, 26% of elderly patients experienced clinically significant blood pressure reductions vs 30% in younger patients, indicating slightly better hemodynamic tolerance 6
• The risk of orthostatic hypotension and falls remains highest in elderly patients on multiple medications, making tamsulosin a safer alternative in this population 3

Critical Drug Interaction Warning

• Doxazosin potentiates orthostatic hypotension when combined with antidepressants and antipsychotics, requiring careful monitoring in psychiatric patients 1
• Separate management of hypertension may be required in patients using doxazosin for LUTS, as alpha-blocker therapy should not be assumed to constitute optimal hypertension management 3

Metabolic Effects

• Weight gain occurs, likely due to extracellular fluid volume expansion and asthenia-related alterations in energy balance 1
• Favorable lipid profile changes include increased HDL cholesterol, increased HDL:total cholesterol ratio, and decreased LDL cholesterol, total cholesterol, and triglycerides 4, 7, 8

Common Pitfalls to Avoid

• Do not use doxazosin in men with hypertension and cardiac risk factors due to elevated congestive heart failure risk demonstrated in ALLHAT 3, 1
• Do not assume doxazosin is the safest alpha-blocker for elderly patients—tamsulosin has the lowest probability of orthostatic hypotension 3
• Initiate therapy at 1 mg/day and titrate at two-week intervals to minimize first-dose orthostatic hypotension 2, 4
• Advise patients planning cataract or glaucoma surgery to inform their ophthalmologist about current or previous doxazosin use 3