What are the recommended doses for combining tadalafil (Cialis) and sildenafil (Viagra) for erectile dysfunction treatment?

Recommended Dosing for Tadalafil and Sildenafil Combination in Erectile Dysfunction

Combination therapy with tadalafil and sildenafil is not recommended for erectile dysfunction treatment as there are no established safe dosing guidelines for this combination and no evidence supporting improved outcomes over monotherapy with either medication alone.

Evidence-Based Approach to PDE5 Inhibitor Therapy

First-Line Treatment Options

• PDE5 inhibitors are the first-line therapy for erectile dysfunction 1
• Each PDE5 inhibitor should be used individually, not in combination:
  • Sildenafil: Starting dose 50mg (range 25-100mg) taken 1 hour before sexual activity, no more than once daily 2
  • Tadalafil: 10-20mg as needed before sexual activity or 5mg once daily 1
  • Vardenafil: 10-20mg as needed before sexual activity 1

Important Safety Considerations

• PDE5 inhibitors work through the same mechanism (inhibition of phosphodiesterase type 5), so combining them:
  • May increase risk of adverse effects including headache, flushing, dyspepsia, and nasal congestion 1
  • Could potentially cause dangerous hypotension 1
  • Has no established safety profile in clinical guidelines

Clinical Evidence on Combination Use

The 2018 AUA guideline on erectile dysfunction does not recommend combining PDE5 inhibitors 1. Only one small study has examined tadalafil 5mg daily combined with sildenafil 50mg as needed 3, but this approach:

• Was only tested in a limited population
• Is not endorsed by major urological guidelines
• Has not been evaluated for long-term safety

Alternative Approaches for Patients with Inadequate Response

For patients who fail to respond to one PDE5 inhibitor:

1. Optimize current therapy first:

   • Ensure proper medication administration (timing, sexual stimulation, avoiding heavy meals) 1
   • Titrate to maximum dosing before declaring treatment failure 1

2. Try a different PDE5 inhibitor:

   • Switching between agents may be beneficial for some patients 1
   • Patient preference studies show many patients prefer tadalafil over sildenafil (71% vs 29%) 4, possibly due to its longer duration of action 5

3. Consider second-line therapies if all PDE5 inhibitors fail:

   • Alprostadil intra-urethral suppositories
   • Intracavernous injections
   • Vacuum constriction devices
   • Penile prostheses 1

Common Pitfalls to Avoid

• Contraindications: Never combine PDE5 inhibitors with nitrates due to risk of severe hypotension 1
• Drug interactions: Use caution with CYP3A4 inhibitors (ritonavir, ketoconazole, erythromycin) which may increase PDE5 inhibitor levels 2
• Inadequate trial: Many "failures" are due to improper use rather than true medication ineffectiveness 1
• Underlying conditions: Address hormonal abnormalities (especially testosterone deficiency) which may limit PDE5 inhibitor effectiveness 1

PDE5 inhibitors should be used individually as monotherapy for erectile dysfunction, with careful attention to proper administration and dosing. If one agent fails, switching to another PDE5 inhibitor or adding testosterone therapy (if deficient) may improve outcomes before moving to more invasive options.