PDE5 Inhibitor: Viagra, Cialis and Their Warnings
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PDE5 inhibitor

Also called phosphodiesterase type 5 inhibitor, sildenafil, tadalafil · Reviewed

Definition: A PDE5 inhibitor is a class of drugs that includes sildenafil (Viagra) and tadalafil (Cialis). The Viagra label approves it for erectile dysfunction. The Cialis label approves it for erectile dysfunction, for symptoms of benign prostatic hyperplasia (BPH), and for both together.

The nitrate rule

The Viagra label (section 4) says it must not be used with nitric oxide donors such as organic nitrates or nitrites in any form, taken regularly or now and then, or with guanylate cyclase stimulators such as riociguat, because blood pressure can drop sharply. Sildenafil is also sold as Revatio for pulmonary arterial hypertension, and the label says the two are not taken together.

Other label warnings

  • Prolonged erection: erections over 4 hours and priapism have been reported and need urgent care.
  • Sudden vision loss: may be a sign of NAION, and the label says to stop all PDE5 inhibitors and get medical attention.

Neither Viagra nor Cialis has a boxed warning. The Viagra label lists headache in 16% to 28% of men vs 7% on placebo, along with flushing, indigestion, vision changes and a stuffy nose. When Cialis is started with finasteride for BPH, its label recommends use for up to 26 weeks.

Why it matters for your log

Cialis can be taken daily or as needed, and the site compares the two schedules. Logging which schedule you are on, and every other medicine, helps a prescriber check for the nitrate conflict and other interactions.

Read more on Dose Track: Viagra side effects · Cialis side effects · Cialis daily vs as needed

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
PriapismPriapism is an erection that will not go down and lasts for hours. The Viagra and Cialis labels describe… NAIONNAION (non-arteritic anterior ischemic optic neuropathy) is a sudden problem with the optic nerve, which… Prescribing informationPrescribing information is the FDA-approved label for a prescription drug, written mainly for health care… Half-lifeHalf-life is the time it takes for the amount of a drug in your body to fall by half. After one half-life,…

Frequently asked questions

Can PDE5 inhibitors be taken with nitrates?+
No. The Viagra label says it must not be used with organic nitrates or nitrites in any form, because blood pressure can drop sharply.
Do Viagra or Cialis have a boxed warning?+
No. Their main warnings cover nitrates, prolonged erections and sudden vision loss.

Sources

  1. Viagra (sildenafil) US prescribing information, DailyMed
  2. Cialis (tadalafil) US prescribing information, DailyMed

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