What are the indications, age criteria, contraindications, and cautions for tamsulosin, silodosin, and mirabegron in adult males and females?

Comprehensive Guide to Tamsulosin, Silodosin, and Mirabegron Use

Tamsulosin

Indications

Tamsulosin is first-line pharmacological treatment for moderate-to-severe lower urinary tract symptoms (LUTS) in men over 50 years old, particularly when voiding symptoms (hesitancy, weak stream, incomplete emptying) predominate. 1

• Approved for male LUTS associated with benign prostatic hyperplasia (BPH) 2
• Can facilitate successful voiding after catheter removal in acute urinary retention 3
• Not FDA-approved for use in females 2
• Contraindicated in men without prostatic enlargement or post-prostatectomy, as the therapeutic target is absent 3

Age Criteria

• Standard patient is a man > 50 years with bothersome moderate-to-severe LUTS 1
• No upper age limit specified, though cardiovascular monitoring is prudent in elderly patients 4

Dosing

• Start at 0.4 mg once daily (modified-release formulation); no titration required 1
• If inadequate response after 2-4 weeks, may escalate to 0.8 mg daily, though additional benefit is minimal 1
• Expect 4-6 point reduction in International Prostate Symptom Score (IPSS) within 2-4 weeks 1

Contraindications and Cautions

Critical Pre-Treatment Screening:

• Screen every patient for planned cataract or glaucoma surgery before initiating tamsulosin 1, 3
• Tamsulosin causes intraoperative floppy iris syndrome (IFIS), complicating ophthalmic procedures 2, 1
• If cataract surgery is imminent, defer tamsulosin or use silodosin instead 1

Sexual Side Effects:

• Ejaculatory dysfunction occurs in 4.5-14% of patients, higher than other α-blockers 1, 4
• Does not affect libido 2

Cardiovascular Effects:

• Minimal blood pressure effects at 0.4 mg dose 1
• Low risk of orthostatic hypotension compared to non-selective α-blockers 4
• Safe to use with sildenafil when patients are monitored for orthostatic symptoms 4

Other Adverse Events:

• Headache, dizziness, generalized weakness, nasal congestion 1
• Asthenia 2

Combination Therapy Indications

Add a 5α-reductase inhibitor (finasteride or dutasteride) when:

• Prostate volume > 30 cc on imaging, OR
• PSA > 1.5 ng/mL, OR
• Palpable prostate enlargement on digital rectal exam, OR
• Goal includes preventing disease progression, urinary retention, or future surgery 1

Add anticholinergics (solifenacin) or mirabegron for:

• Men with mixed voiding and storage symptoms (urgency, frequency) 3

---

Silodosin

Indications

Silodosin is indicated for male LUTS associated with BPH, with exceptional selectivity for α1A-adrenoceptors over α1B-adrenoceptors (583-fold), minimizing cardiovascular effects. 5, 6

• Approved for male LUTS/BPH 6
• Not FDA-approved for use in females
• Particularly beneficial when maximizing cardiovascular tolerability is essential 5
• Alternative to tamsulosin when cataract surgery is planned 1

Age Criteria

• Studied in men > 50 years with BPH 7
• Excellent cardiac and blood pressure safety profile makes it suitable for elderly patients 5

Dosing

• 8 mg once daily after dinner 7
• Dosage adjustment recommended in moderate renal impairment 5
• Safe in mild-to-moderate liver dysfunction 5

Contraindications and Cautions

Drug Interactions:

• Do not use with potent CYP3A4 inhibitors 5

Sexual Side Effects:

• Retrograde or abnormal ejaculation occurs in > 22% of patients, significantly higher than tamsulosin 6, 7
• May be troublesome for sexually active patients 7

Cardiovascular Effects:

• Incidence of orthostatic hypotension < 3% 6
• Does not promote QT-interval prolongation 5
• Dizziness incidence similar to tamsulosin 8

Efficacy:

• Significantly improves IPSS and maximum urinary flow rate (Qmax) compared to placebo 6
• In head-to-head trials, silodosin showed superior improvement in IPSS total score and quality of life compared to tamsulosin 8
• Particularly effective for straining and nocturia 8

---

Mirabegron

Indications

Mirabegron is a β3-adrenoceptor agonist approved for overactive bladder (OAB) in both males and females, and serves as add-on therapy to α-blockers in men with persistent storage symptoms. 2, 9

• Primary indication: OAB with urgency, urge urinary incontinence, and daytime frequency in males and females 2
• Add-on therapy: Men with LUTS on tamsulosin who continue to experience OAB symptoms 9
• Can be combined with solifenacin for enhanced efficacy 2

Age Criteria

• Studied in adult males and females with OAB 2
• Safe and effective in older patients with multiple comorbidities 2
• No specific age restrictions, though cardiovascular monitoring is appropriate in elderly patients 2

Dosing

• Standard dose: 50 mg once daily 9
• 25 mg dose available for older patients with multiple comorbidities 2

Contraindications and Cautions

Efficacy in Males:

• As add-on to tamsulosin, mirabegron significantly improves micturitions per 24 hours, mean volume voided per micturition, OAB symptom score, IPSS total and storage scores, and quality of life 9
• Differences in urgency, urgency urinary incontinence, and nocturia versus placebo were not statistically significant in the MATCH trial 9

Safety Profile:

• Well tolerated with no major safety concerns 9
• Excellent cardiovascular safety profile in integrated clinical trial database 2
• Safe in patients with hypertension 2

Patient Selection:

• Men with PSA < 1.3 ng/mL may benefit more from muscarinic receptor antagonists, though mirabegron is an alternative 2
• Prescribe with caution in men with low post-void residual (PVR) at baseline (< 150 mL) 2
• Regular re-evaluation of IPSS and PVR is recommended 2
• Acute urinary retention is rare in men with low baseline PVR 2

Adverse Events:

• Common side effects include dry mouth, constipation, dizziness, nasopharyngitis 2
• Voiding difficulties including increased PVR can occur, though AUR is rare 2

---

Key Clinical Algorithms

Choosing Between Tamsulosin and Silodosin

Use silodosin when:

• Cataract surgery is planned or anticipated 1
• Maximizing cardiovascular tolerability is critical 5
• Patient is sexually inactive or unconcerned about ejaculatory dysfunction 7

Use tamsulosin when:

• No planned ophthalmic surgery 1
• Patient is sexually active and wishes to minimize ejaculatory dysfunction risk 1
• Simplicity of once-daily dosing without food restrictions is preferred 1

Adding Mirabegron to α-Blocker Therapy

Add mirabegron 50 mg daily when:

• Male patient on tamsulosin continues to experience urgency, frequency, or urge incontinence 9
• Patient has low baseline PVR (< 150 mL) 2
• Antimuscarinic side effects (dry mouth, constipation, cognitive effects) are unacceptable 9

Monitor:

• IPSS and PVR regularly 2
• Blood pressure in patients with hypertension 2
• Voiding difficulties or increased PVR 2