Phosphodiesterase-5 Inhibitors

Key Points

• PDE5 inhibitors (sildenafil, tadalafil, vardenafil) enhance nitric-oxide-mediated smooth-muscle relaxation.
• Primary indications include erectile dysfunction and pulmonary arterial hypertension.
• Tadalafil is the urinary-focused PDE5 agent used for BPH symptom control, commonly at 5 mg once daily.
• Absolutely contraindicated with nitrate medications due to risk of severe life-threatening hypotension.
• Also avoid concomitant guanylate cyclase stimulants because profound hypotension can occur.
• ED dosing is generally limited to one dose per day; avanafil has the fastest onset option (about 15 minutes before sexual activity).
• Common side effects include headache, flushing, nasal congestion, and visual disturbances.
• Monitor urgently for prolonged erection/priapism and sudden vision or hearing loss.

Mechanism of Action

PDE5 inhibitors block the enzyme phosphodiesterase type 5, which normally degrades cyclic GMP (cGMP). By preserving cGMP, these agents enhance the vasodilatory effect of nitric oxide on smooth muscle. In erectile tissue, this increases blood flow and facilitates erection. In pulmonary vasculature, it reduces pulmonary arterial pressure.

Indications

• Erectile dysfunction (sildenafil, tadalafil, vardenafil, avanafil).
• Pulmonary arterial hypertension (sildenafil, tadalafil at different doses).
• Benign prostatic hyperplasia (tadalafil).

Tadalafil for BPH

For BPH pathways, tadalafil is typically dosed as 5 mg orally once daily at approximately the same time each day.

Renal-dose considerations:

• Creatinine clearance 30-50 mL/min: initial 2.5 mg once daily; may increase to 5 mg based on response/tolerability.
• Creatinine clearance less than 30 mL/min or hemodialysis: once-daily tadalafil use for BPH is not recommended.

Erectile Dysfunction Dosing Reference

Drug	Typical On-Demand ED Dose	Timing Before Sexual Activity	Maximum Frequency
Sildenafil	50 mg (range 25-100 mg)	About 60 minutes	1 dose/day
Tadalafil	10 mg (range 5-20 mg)	About 60 minutes	1 dose/day
Vardenafil	10 mg (range 5-20 mg)	About 60 minutes	1 dose/day
Avanafil	100 mg (range 50-200 mg)	As early as about 15 minutes	1 dose/day

Nursing Considerations

• Absolute contraindication: Concurrent use with any form of nitrate or nitric-oxide donor medication — can cause severe, potentially fatal hypotension.
• Concomitant alpha-adrenergic blocker use can trigger severe hypotension and is generally avoided unless a specialist-directed staggered dosing plan is used.
• Also avoid guanylate cyclase stimulants due to dangerous blood-pressure decline risk.
• Assess for concurrent use of alpha-blockers, antihypertensives, strong CYP3A4 inhibitors, and substantial alcohol intake because symptomatic hypotension risk increases.
• Evaluate cardiovascular status; clients should have sufficient cardiac reserve for sexual activity.
• Use additional caution or defer treatment with recent major cardiovascular instability (for example MI, stroke, severe arrhythmia, unstable angina, or decompensated heart failure in recent months), or with resting BP below about 90/50 mm Hg or above about 170/110 mm Hg.
• Sildenafil and vardenafil are typically taken 30 to 60 minutes before activity; tadalafil has a longer duration (up to 36 hours).
• Assess for hepatic and renal impairment; dose adjustment may be required.
• Use additional caution in older adults with reduced hepatic, renal, or cardiac function.
• Monitor for erection longer than 4 hours and painful erection longer than 6 hours (priapism emergency pattern).
• Monitor for sudden vision or hearing change/loss and escalate immediately.
• Verify medication list includes OTC products and nitrate exposure history before administration.

Side Effects and Adverse Effects

• Common: Headache, facial flushing, nasal congestion, dyspepsia.
• Visual/otologic: Blue-tinted vision, blurred vision, light sensitivity (especially sildenafil), and possible sudden hearing change/loss.
• Serious: Severe hypotension with nitrates, priapism, vaso-occlusive crisis risk in sickle-cell-disease, non-arteritic anterior ischemic optic neuropathy (rare).

Nitrate Interaction

PDE5 inhibitors with nitrates (nitroglycerin, isosorbide) can cause fatal hypotension. This combination is absolutely contraindicated. Assess all medication lists for any nitrate form before prescribing.

Health Teaching

• Do not take with any nitrate medication (including recreational nitrate inhalers) — life-threatening blood pressure drop can occur.
• Avoid nitrate exposure for at least 24-48 hours after PDE5 inhibitor dosing (agent-dependent) unless emergency care directs otherwise.
• Do not combine with guanylate cyclase stimulants, alpha blockers, antihypertensives, or strong CYP3A4 inhibitors without prescriber-directed plan.
• Report an erection lasting more than 4 hours or sudden vision or hearing changes immediately.
• Seek emergency care for chest pain after use; do not self-administer nitrates.
• Avoid substantial alcohol intake because hypotension risk increases.
• Rise slowly from sitting or lying positions if dizziness occurs.
• The medication enhances natural arousal response; sexual stimulation is still required.
• For pulmonary hypertension indication, take as scheduled (not on-demand).

Related Concepts

• Nitrates - Absolutely contraindicated concurrent use.
• pulmonary-hypertension-in-congenital-heart-disease-and-pphn - Pulmonary vasodilator indication context.
• benign-prostatic-hyperplasia - Additional indication for tadalafil.
• sickle-cell-disease - Priapism and vaso-occlusive complications increase risk complexity with sildenafil exposure.

Self-Check

1. Why are PDE5 inhibitors absolutely contraindicated with nitrate medications?
2. How does the mechanism of action differ between erectile dysfunction and pulmonary hypertension indications?
3. What constitutes a urologic emergency related to PDE5 inhibitor use?