Pathophysiology and Management of Erectile Dysfunction

• Metabolic and Cardiovascular: Diabetes Mellitus (DM), Hypertension (HTN), and arteriosclerosis.
• Neurological: Multiple Sclerosis (MS), Parkinson's disease, spinal cord injuries, and cerebral trauma.
• Other: Low testosterone, liver cirrhosis, and prostate diseases such as BPH or cancer.

Psychological Causes

Mental health plays a significant role in sexual function. Anxiety, depression, stress, guilt, and general feelings of inadequacy or relationship issues can prevent the initiation of the arousal cascade.

Drug-Induced Erectile Dysfunction

Several classes of medications can inadvertently cause ED by interfering with cardiovascular, central nervous, or genitourinary systems:

• Cardiovascular: Beta-blockers (e.g., propranolol), diuretics (e.g., HCTZ), and cardiac glycosides like digoxin.
• Central Nervous System (CNS): SSRIs (e.g., fluoxetine), TCAs (e.g., amitriptyline), antipsychotics (e.g., chlorpromazine), and mood stabilizers (e.g., lithium).
• Genitourinary (GU): 5-alpha-reductase inhibitors.

Management Strategies

Management follows a tiered approach, beginning with diagnosis and moving toward more invasive interventions if necessary.

Diagnosis

A thorough workup includes a physical examination, history of present illness (PMH), and hormone analysis (testing Testosterone, LH, TSH, and prolactin). Clinicians also screen for comorbidities like DM and HTN and may use ultrasound or dynamic infusion cavernosometry to assess blood flow.

Tiered Treatment Approach

1. 1st Line: Therapeutic lifestyle changes (TLCs) such as exercise and smoking cessation, adjusting medications if the cause is drug-induced, and psychotherapy.
2. 2nd Line: PDE5 Inhibitors (e.g., Sildenafil, Tadalafil, Vardenafil).
3. 3rd Line: Prostaglandin E1 (Alprostadil) via transurethral or intracavernous routes, vasodilators combined with alpha-blockers (papaverine/phentolamine), or surgical penile prosthesis implants.

Pharmacotherapy: PDE5 Inhibitors and Sildenafil

PDE5 inhibitors work by inhibiting the enzyme that breaks down cGMP. By blocking PDE5, these drugs maintain higher levels of cGMP, resulting in harder and longer-lasting erections.

Sildenafil (Viagra) Profile

Sildenafil is a well-known agent in this class. Its pharmacokinetics and safety profile are critical for patient education:

• Metabolism: It is metabolized via the CYP3A4 enzyme pathway.
• Bioavailability: High-fat meals can decrease its bioavailability.
• Onset/Duration: It typically reaches peak concentration within 1 hour and has a duration of action (DOA) of 2–4 hours.

💡 Exam Tip: Drug Interactions

Always check if a patient is taking nitrates. The concurrent use of nitrates and PDE5 inhibitors is contraindicated because both increase cGMP levels, which can lead to severe, life-threatening hypotension.

Adverse Effects and Contraindications

Common side effects include headache, flushing, dyspepsia, nasal congestion, and dizziness.

Serious but rare complications include:

• NAION: Non-arteritic anterior ischemic optic neuropathy, which can cause irreversible vision loss.
• Priapism: A painful erection lasting >4 hours. This is a medical emergency that requires immediate attention to prevent permanent penile tissue damage and necrosis.

Contraindications and Precautions:

• Cardiovascular Safety: Patients should avoid use if they have had a recent cardiovascular event (MI, stroke, or dysrhythmia) within the last 6 months, or if they have unstable blood pressure (resting hypotension < 90/50 mmHg or hypertension > 170/110 mmHg).
• Alpha-1 Blockers: Use with caution due to the risk of postural hypotension.
• CYP3A4 Inhibitors: Medications like ketoconazole, erythromycin, or even grapefruit juice can interact with the metabolism of Sildenafil.

Summary Table of PDE5 Inhibitors

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Practice Questions

Question 1: A patient has been prescribed sildenafil [Viagra] for erectile dysfunction. Which instruction should the nurse include in the teaching plan? A. Take the medication on an empty stomach. B. Drink plenty of fluids to prevent priapism. C. Avoid taking nitroglycerin with this drug. D. Constipation is a common adverse effect. Answer: C. Concurrent use with nitrates is contraindicated due to the risk of severe hypotension.

Question 2: The nurse should instruct a patient prescribed sildenafil [Viagra] to avoid taking this medication with what? A. Milk B. Crackers C. Eggs D. Grapefruit juice Answer: D. Grapefruit juice can affect CYP3A4 metabolism, potentially altering drug levels.