McKenna's Pharmacology for Nursing, 2e

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P A R T 7  Drugs acting on the reproductive system

TABLE 41.3

DRUGS IN FOCUS Drugs used to treat penile erectile dysfunction

Drug name

Dosage/route

Usual indications

alprostadil (Caverject)

2.5 mcg injected intracavernously, titrate the dose to one that will allow a satisfactory erection that is maintained no longer than 1 hour; mean dose after 6 months is reported to be 20.7 mcg Viagra: 25–100 mg PO taken 1 hour before sexual stimulation Revatio: 20 mg PO t.d.s., at least 4–6 hours apart 10 mg PO taken before sexual activity; range 5–20 mg PO; limit use to once a day; 2.5–5 mg/day PO for very sexually active males 5–10 mg PO taken 1 hour before sexual stimulation; range 5–20 mg; limit use to once a day

Treatment of penile erectile dysfunction

Treatment of penile erectile dysfunction

sildenafil (Viagra, Revatio)

Treatment of pulmonary arterial hypertension in men and women Treatment of penile erectile dysfunction

tadalafil (Cialis)

vardenafil (Levitra)

Treatment of penile erectile dysfunction

Contraindications and cautions These drugs are contraindicated in the presence of any anatomical obstruction or condition that might pre- dispose to priapism. They cannot be used with penile implants, and they are not indicated for use in women. However, sildenafil is used in women for the treatment of pulmonary arterial hypertension. Caution should be used in people with bleeding disorders. The PDE5 inhibitors should also be used cau- tiously in people with coronary artery disease, active peptic ulcer, retinitis pigmentosa, optic neuropathy, hypotension or severe hypertension, congenital pro- longed QT interval or severe hepatic or renal disorders because of the risk of exacerbating these diseases.

Adverse effects Adverse effects associated with alprostadil are local effects such as pain at the injection site, infection, priapism, fibrosis and rash. The PDE5 inhibitors are associated with more systemic effects, including headache, flushing (related to relaxation of vascular smooth muscle), dyspepsia, urinary tract infection, diar- rhoea, dizziness, possible optic neuropathy, possible eighth cranial nerve toxicity, loss of hearing and rash. Clinically important drug–drug interactions The PDE5 inhibitors cannot be taken in combination with any organic nitrates or alpha-adrenergic blockers; Prototype summary: Sildenafil Indications: Treatment of erectile dysfunction in the presence of sexual stimulation; treatment of pulmonary arterial hypertension. Actions: Inhibits PDE5 receptors, leading to a release of nitrous oxide, which activates cGMP to cause a prolonged smooth muscle relaxation, allowing the flow of blood into the corpus cavernosum and facilitating erection. Pharmacokinetics: Route Onset Peak Duration PO 15–30 mins 30–120 mins 4 hours T 1/2 : 4 hours, with hepatic metabolism and excretion in the faeces and urine. Adverse effects: Headache, abnormal vision, flushing, dyspepsia, urinary tract infection, rash.

Safe medication administration

People who are using PDE5 inhibitors need to be advised to avoid drinking grapefruit juice while using the drug. Grapefruit juice can cause a decrease in the metabolism of the PDE5 inhibitor, leading to increased serum levels and a risk of toxicity. They should also be advised to avoid taking the drug with or just after a high-fat meal. The presence of fat in the GI tract will delay the absorption and onset of action of the drug, which could cause problems for individuals who are timing onset of action with their sexual activity. These drugs can have serious cardiovascular effects. Deaths have been reported in people combining use of such drugs with other cardiovascular medications. People need to be aware of the potential risks in taking the drugs alongside other medications.