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Pharmacology for Nurses

35.5 Phosphodiesterase 5 Inhibitors

Pharmacology for Nurses35.5 Phosphodiesterase 5 Inhibitors

Learning Outcomes

By the end of this section, you should be able to:

  • 35.5.1 Identify the characteristics of phosphodiesterase 5 inhibitors used to treat benign prostatic hyperplasia.
  • 35.5.2 Explain the indications, actions, adverse reactions, contraindications, and interactions of phosphodiesterase 5 inhibitors used to treat benign prostatic hyperplasia.
  • 35.5.3 Describe nursing implications of phosphodiesterase 5 inhibitors used to treat benign prostatic hyperplasia.
  • 35.5.4 Explain the client education related to phosphodiesterase 5 inhibitors used to treat benign prostatic hyperplasia.

Phosphodiesterase 5 (PDE5) inhibitors are a class of medications primarily used to treat erectile dysfunction and, in some cases, pulmonary hypertension and benign prostatic hyperplasia (BPH). These drugs work by blocking the action of an enzyme called phosphodiesterase type 5, which is responsible for breaking down cyclic guanosine monophosphate (cGMP) in the body; cGMP is a molecule that plays a crucial role in relaxing smooth muscles and increasing blood flow to various tissues, including the penis and the lungs.


Tadalafil (Cialis) is the PDE5 inhibitor that has been approved by regulatory agencies to treat both erectile dysfunction and lower urinary tract symptoms associated with BPH. This chapter covers tadalafil in relation to BPH only. Tadalafil works by relaxing the smooth muscles in the prostate and bladder, which can help improve urine flow and reduce the urinary symptoms caused by prostate enlargement. These effects are achieved through the drug’s effect on cGMP, the same pathway that plays a role in erectile function.

Adverse Effects and Contraindications

Common adverse effects include headache, dyspepsia, back pain, myalgia, nasal congestion, pain in limbs, flushing, cough, and UTI. The drug is contraindicated in clients who are taking nitrates or guanylate cyclase stimulants or who are hypersensitive to the drug or any of its components (DailyMed, Tadalafil, 2023).

Table 35.7 is a drug prototype table for phosphodiesterase 5 inhibitors for treatment of BPH featuring tadalafil. It lists drug class, mechanism of action, adult dosage, indications, therapeutic effects, drug and food interactions, adverse effects, and contraindications.

Drug Class
Phosphodiesterase 5 inhibitor

Mechanism of Action
Increases cGMP levels
Promotes the relaxation of smooth muscles in the prostate and the bladder neck
Drug Dosage
For BPH: 5 mg orally once daily, taken at approximately the same time every day.
For renal impairment, creatinine clearance 30–50 mL/min: Initial dose: 2.5 mg orally; an increase to 5 mg may be considered based on individual response.
Creatinine clearance less than 30 mL/min or clients receiving hemodialysis: Tadalafil tablets for once-daily use are not recommended.
Treatment of erectile dysfunction
Treatment of the signs and symptoms of benign prostatic hyperplasia

Therapeutic Effects
Alleviates urinary symptoms related to benign prostatic hyperplasia
Drug Interactions
Alpha blockers
CYP3A4 inhibitors
Guanylate cyclase stimulants
Substantial consumption of alcohol

Food Interactions
No significant interactions
Adverse Effects
Back pain
Nasal congestion
Pain in limbs
Sudden vision or hearing loss
Prolonged erection or priapism
Guanylate cyclase stimulants
Hypersensitivity reactions
Table 35.7 Drug Prototype Table: Tadalafil (source:

Nursing Implications

The nurse should do the following for clients who are taking PDE5 inhibitors to treat BPH:

  • Before administering the drug, check the client’s medical history, current drug list (including over-the-counter medications and alcohol), and allergies.
  • Before administering the drug, determine the client’s regular or intermittent use of organic nitrates. Concomitant use of these with tadalafil can cause a sudden drop in blood pressure to an unsafe level, resulting in dizziness, syncope, or myocardial infarction (DailyMed, Tadalafil tablet, 2023).
  • Monitor for erections lasting longer than 4 hours and for priapism (painful erections lasting longer than 6 hours).
  • Monitor closely for sudden vision or hearing loss because this can be a serious adverse effect of tadalafil.
  • Provide client teaching regarding the drug and when to call the health care provider. See below for additional client teaching guidelines.

Client Teaching Guidelines

The client taking a PDE5 inhibitor for BPH should:

  • Take the medication as prescribed by their health care provider.
  • Notify their health care provider if sudden symptoms of vision or hearing loss occur or if they have an erection lasting longer than 4 hours or a painful erection lasting longer than 6 hours.
  • Avoid getting up too fast from a sitting or lying position because this drug may cause a vasomotor response that includes dizziness.

The client taking a PDE5 inhibitor for BPH should not:

  • Take tadalafil with nitrates, antihypertensives, alpha blockers, or CYP3A4 inhibitors because concomitant use may cause serious adverse effects, such as an unsafe drop in blood pressure, dizziness, and syncope.
  • Consume substantial amounts of alcohol with tadalafil due to hypotensive effects.

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