Is Anastrozole (Aromatase inhibitor) safe to use with Viagra (Sildenafil)?

Anastrozole and Viagra (Sildenafil) Combination Safety

Anastrozole can be safely used with Viagra (sildenafil) as there are no known significant drug interactions between these medications, but patients should be monitored for potential additive effects on blood pressure.

Pharmacological Considerations

Anastrozole

• Anastrozole is an aromatase inhibitor primarily used for:
  • Reducing risk of invasive breast cancer in postmenopausal women at increased risk 1
  • Treatment of hormone receptor-positive breast cancer in postmenopausal women 1
• Common side effects include:
  • Joint stiffness and arthralgias
  • Vasomotor symptoms
  • Hypertension
  • Dry eyes
  • Vaginal dryness 1, 2

Viagra (Sildenafil)

• Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor that causes vasodilation
• Primary side effects are related to its vasodilatory properties:
  • Headache
  • Flushing
  • Dyspepsia due to relaxation of gastroesophageal sphincter 3

Safety of Combination Use

No Direct Interaction

• There is no evidence in the medical literature of a direct pharmacological interaction between anastrozole and sildenafil
• The medications work through different mechanisms:
  • Anastrozole inhibits aromatase enzyme
  • Sildenafil inhibits PDE5 enzyme

Blood Pressure Considerations

• Both medications can affect blood pressure:
  • Anastrozole may cause hypertension in some patients 1
  • Sildenafil causes mild to moderate vasodilation 3
• The combination may lead to additive but not potentiating effects on blood pressure 4

Important Precautions

Cardiovascular Considerations

1. Sildenafil contraindications that must be observed:

   • Concurrent use of organic nitrates is absolutely contraindicated due to risk of severe hypotension 3, 5
   • Use with caution in patients with:
     • Unstable angina
     • Recent myocardial infarction (within 6 months)
     • Recent stroke (within 6 months)
     • Cardiac failure 3

2. Blood pressure monitoring:

   • Patients on both medications should have their blood pressure monitored, especially when starting the combination
   • Sildenafil may cause additive blood pressure decreases when combined with antihypertensive medications 4

Clinical Management Algorithm

1. Before starting combination:

   • Assess cardiovascular status and risk factors
   • Ensure patient is not taking organic nitrates
   • Check baseline blood pressure

2. Dosing considerations:

   • Start with standard dosing of anastrozole (1 mg/day) 1
   • Consider starting with lower dose of sildenafil (25mg) in patients with:
     • Multiple antihypertensive medications
     • Borderline low blood pressure
     • Advanced age

3. Monitoring:

   • Monitor blood pressure after initiating combination therapy
   • Assess for symptoms of hypotension (dizziness, lightheadedness)
   • Continue regular monitoring of anastrozole-related side effects, particularly bone health 1, 2

4. Patient education:

   • Instruct patients to report symptoms of significant hypotension
   • Advise patients not to take sildenafil within 24 hours of nitrate medications
   • Explain that mild headache or flushing may occur with sildenafil use

Conclusion

The combination of anastrozole and sildenafil appears to be safe for most patients, with no documented significant drug interactions. The main consideration is potential additive effects on blood pressure, which can be managed through appropriate monitoring and dose adjustment if needed.