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Phosphodiesterase-5 Inhibitors

2 min read

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.
  • Absolutely contraindicated with nitrate medications due to risk of severe life-threatening hypotension.
  • Common side effects include headache, flushing, nasal congestion, and visual disturbances.

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).

Nursing Considerations

  • Absolute contraindication: Concurrent use with any form of nitrate or nitric-oxide donor medication — can cause severe, potentially fatal hypotension.
  • Assess for concurrent use of alpha-blockers, which also potentiate hypotension.
  • Evaluate cardiovascular status; clients should have sufficient cardiac reserve for sexual activity.
  • 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.
  • Monitor for priapism (erection lasting more than 4 hours), which is a urologic emergency.

Side Effects and Adverse Effects

  • Common: Headache, facial flushing, nasal congestion, dyspepsia.
  • Visual: Blue-tinted vision, blurred vision, light sensitivity (especially sildenafil).
  • Serious: Severe hypotension with nitrates, priapism, sudden hearing loss (rare), 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.
  • Report an erection lasting more than 4 hours or sudden vision or hearing changes immediately.
  • Avoid grapefruit juice, which can increase drug levels.
  • The medication enhances natural arousal response; sexual stimulation is still required.
  • For pulmonary hypertension indication, take as scheduled (not on-demand).

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?

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