36.7: Phosphodiesterase 5 Inhibitors
By the end of this section, you should be able to:
- 36.7.1 Identify the characteristics of phosphodiesterase 5 inhibitor drugs used to treat erectile dysfunction.
- 36.7.2 Explain the indications, actions, adverse reactions, and interactions of phosphodiesterase 5 inhibitor drugs used to treat erectile dysfunction.
- 36.7.3 Describe nursing implications of phosphodiesterase 5 inhibitor drugs used to treat erectile dysfunction.
- 36.7.4 Explain the client education related to phosphodiesterase 5 inhibitor drugs used to treat erectile dysfunction.
Phosphodiesterase 5 (PDE5) inhibitors are used to treat erectile dysfunction. PDE5 is an enzyme located within the walls of blood vessels that impacts blood flow. PDE5 inhibitors prevent the PDE5 enzyme from functioning, which results in the relaxation of the blood vessels and increased blood flow. PDE5 inhibitors work in cases when blood flow to the corpus cavernosum is inadequate, such as in aging or due to vascular or neurological problems. However, these medications cannot be used for every cause of erectile dysfunction, and they do have serious side effects if taken incorrectly, such as taking more than one dose in 24 hours or taking with nitroglycerin. Sildenafil, tadalafil, avanafil, and vardenafil are the common PDE inhibitors. (Use of PDE5 inhibitors for treating benign prostatic hyperplasia is discussed in Urinary and Bladder Disorder Drugs).
Table 36.24 lists common PDE5 inhibitors and typical routes and dosing for adult clients.
| Drug | Routes and Dosage Ranges |
|---|---|
|
Sildenafil
( Viagra ) |
50 mg orally, as needed, approximately 60 minutes before sexual activity.
Dose range: 25–100 mg. Maximum of 1 dose/day. |
|
Tadalafil
( Cialis ) |
10 mg orally, as needed, approximately 60 minutes before sexual activity. Dose range: 5–20 mg. Maximum of 1 dose/day. |
|
Avanafil
( Stendra ) |
100 mg orally, as needed, as early as approximately 15 minutes before sexual activity.
Dose range: 50–200 mg. Maximum of 1 dose/day. |
|
Vardenafil
( Levitra ) |
10 mg orally, as needed, approximately 60 minutes before sexual activity. Dose range: 5–20 mg. Maximum of 1 dose/day. |
Adverse Effects and Contraindications
Contraindications for PDE5 inhibitors include the concomitant use of nitrates or alpha-adrenergic blockers, medications often prescribed for cardiovascular problems. The drug interaction can cause life-threatening hypotension and death. Another contraindication is any obstructive condition or anatomical deformation of the penis (DailyMed, Viagra , 2019; Dhaliwal & Gupta, 2023).
Table 36.25 is a drug prototype table for PDE5 inhibitors featuring sildenafil. 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 Smooth muscle relaxation and inflow of blood to the corpus cavernosum |
Drug Dosage
50 mg orally, as needed, approximately 1 hour before sexual activity. Dose range: 25–100 mg. Maximum of 1 dose/day. |
|
Indications
Male erectile dysfunction Therapeutic Effects Enhanced penile erection |
Drug Interactions
Nitrates (all forms) Alpha blockers Strong CYP3A4 inhibitors Food Interactions No significant interactions |
|
Adverse Effects
Headaches Flushing Symptoms resembling those of the common cold Stomach upset Muscle and back pain Dizziness, lightheadedness Nausea Abnormal vision Nasal congestion |
Contraindications
Known hypersensitivity to the drug or its components Caution: History of heart attack, heart failure, angina, severe arrhythmia, or stroke in the last 6 months Hypotension or hypertension (resting BP <90/50 mm Hg or BP >170/110 mm Hg) Hepatic impairment Severe renal impairment Anatomical deformation of the penis |
Nursing Implications
The nurse should do the following for clients who are taking phosphodiesterase 5 inhibitors:
- Assess understanding of indication for specific drug therapy and ability to comprehend instructions.
- Perform physical assessment as appropriate and obtain any diagnostic testing necessary.
- Obtain list of current medications and any OTC or herbal remedies the client uses, especially regarding nitrates and alpha blockers.
- Assess past medical history and family history for cardiovascular disease (heart attack, stroke, hypertension, serious arrhythmias), prostate cancer, BPH, and liver or renal disease.
- Assess smoking history and use of alcohol.
- Assess ability to administer drug at home and follow medication regimen.
- Provide client teaching regarding the drug and when to call the health care provider. See below for client teaching guidelines.
Client Teaching Guidelines
The client taking a phosphodiesterase 5 inhibitor should:
- Understand the medication’s purpose, side effects, contraindications, and precautions.
- Monitor any signs and symptoms of adverse effects and report those that require immediate attention (e.g., vision or hearing loss, priapism).
- Know how to manage the side effects of the specific drug therapy.
- Understand drug, food, and/or herbal interactions that could be harmful.
- Verbalize the importance of follow-up appointments to manage the medication regimen and to observe for adverse effects.
The client taking a phosphodiesterase 5 inhibitor should not:
- Take nitrates and alpha blockers within 48 hours of taking PDE5 inhibitors.
- Take these medications after a high-fat meal.
FDA Black Box Warning
Phosphodiesterase 5 (PDE5) Inhibitors
PDE5 inhibitors can cause:
- Severe hypotension and death when used within 48 hours of any form of nitrate medication
- Prolonged erection greater than 4 hours and priapism (painful erections greater than 6 hours in duration)
- Sudden loss of vision in one or both eyes (may be a sign of nonarteritic anterior ischemic optic neuropathy)
- Sudden decrease in or loss of hearing