Can Finasteride and Sanctura (Trospium) Be Prescribed Together?
Yes, a healthcare provider can safely prescribe finasteride and Sanctura (trospium) together, as there are no clinically significant drug interactions between these medications. 1
Evidence for Safety of Co-Administration
No Drug Interactions Identified
The FDA label for finasteride explicitly states that finasteride does not appear to affect the cytochrome P450-linked drug metabolizing enzyme system, and no clinically meaningful interactions have been identified with multiple drug classes 1
Finasteride was concomitantly used in clinical studies with multiple medication classes without evidence of clinically significant adverse interactions, and while antimuscarinics (the class to which trospium belongs) are not specifically listed, the broad safety profile supports co-administration 1
Clinical Evidence Supporting Combination Use
Moderate-quality evidence demonstrates that trospium reduces urgency urinary incontinence episodes regardless of whether patients are receiving other concomitant drugs 2
Research specifically examining trospium in patients taking multiple concomitant medications (≥7 drugs) found that trospium chloride extended release was safe and effective, with the probability of adverse events influenced by the number of concomitant medications rather than trospium itself 3
The adjusted odds ratio for experiencing any adverse event with trospium versus placebo was 1.19 (95% CI 0.85-1.67; p=0.31), indicating no significant increase in adverse events when combined with other medications 3
Clinical Context for Combined Use
When This Combination Is Appropriate
Men with BPH and overactive bladder symptoms: Finasteride treats prostatic enlargement (prostate volume >30cc) causing obstructive voiding symptoms, while trospium addresses storage symptoms (urgency, frequency, nocturia) 2
Women with urinary incontinence taking finasteride for other indications: Though uncommon, if a woman requires finasteride (off-label use) and has urinary incontinence, trospium can be safely added 2
Triple Therapy Considerations
The European Association of Urology recommends that antimuscarinic agents (like trospium) can be safely added to combination therapy with alpha-blockers and 5-alpha-reductase inhibitors (like finasteride) for men with both voiding and storage symptoms 4, 5
Before adding trospium to finasteride therapy, measure post-void residual (PVR) urine volume; a PVR <150 mL is considered safe for adding antimuscarinic therapy, while PVR >150 mL is a contraindication 5
Important Safety Considerations
Monitoring Parameters
Anticholinergic burden: Patients taking ≥7 concomitant medications experience more adverse effects than those taking fewer medications, though this is related to polypharmacy rather than specific drug interactions 2, 3
Common adverse effects of trospium: Dry mouth, constipation, blurred vision, and dizziness are the most frequently reported antimuscarinic side effects (NNTH 8 for any adverse event) 2
Finasteride-specific effects: Sexual dysfunction (decreased libido 6.4% in first year, ejaculatory dysfunction 3.7% in first year) and 50% reduction in PSA levels after 1 year of therapy 2, 4
Common Pitfalls to Avoid
Failing to assess PVR before adding trospium: Always measure PVR to ensure the patient is not at risk for urinary retention when adding an antimuscarinic to existing BPH therapy 5
Not adjusting PSA interpretation: When screening for prostate cancer in men on finasteride, double the measured PSA value after 1 year of therapy for accurate interpretation 2, 4
Inadequate trial duration: Allow at least 3-6 months to assess finasteride's effectiveness before adding additional agents, as 5-alpha-reductase inhibitors have a slow onset of action 2, 6
Clinical Algorithm for Combined Prescribing
Confirm appropriate indication for finasteride: Prostate volume >30cc with moderate-to-severe lower urinary tract symptoms (AUA Symptom Score >8) 2, 6
Assess for storage symptoms warranting trospium: Urgency, frequency, nocturia, or urge incontinence that persists despite finasteride therapy 2, 5
Measure post-void residual: Ensure PVR <150 mL before initiating trospium 5
Initiate combination therapy: Finasteride 5 mg daily plus trospium chloride 20 mg twice daily (immediate release) or 60 mg once daily (extended release) 2, 3
Monitor for adverse effects: Assess for anticholinergic side effects (dry mouth, constipation, cognitive changes in elderly) and sexual dysfunction from finasteride 2, 3
Reassess at 3-6 months: Evaluate symptom improvement and consider surgical referral if symptoms remain bothersome despite optimized medical therapy 5