Nursing care
Sildenafil: what to check before you give it
Written and reviewed by Dana Whitfield, RN, MSN · 5 min read · Updated September 2026
Short answer
Sildenafil is a PDE5 inhibitor used for erectile dysfunction and pulmonary arterial hypertension. It must never be given within 24 to 48 hours of a nitrate, because the combined vasodilation causes a severe, potentially fatal drop in blood pressure. Always ask about nitrate use, including nitroglycerin, before administering or before a chest-pain patient receives one.
What it does and why it is prescribed
Sildenafil inhibits phosphodiesterase type 5 (PDE5), the enzyme that breaks down cyclic GMP in smooth muscle. Blocking it prolongs the vasodilatory effect of nitric oxide, which in the penis increases blood flow to produce and sustain an erection, and in the pulmonary vasculature lowers pulmonary artery pressure.
That gives it two distinct indications: erectile dysfunction, usually taken as needed before sexual activity, and pulmonary arterial hypertension, taken on a fixed schedule as ongoing therapy. The same drug, two very different dosing patterns and two very different patient populations — a PAH patient on sildenafil is not taking it recreationally or occasionally, and that distinction matters for how you counsel and monitor.
Nursing considerations before giving it
The single question that matters most before any dose: has this patient taken a nitrate, in any form, within the last 24 to 48 hours? That includes sublingual nitroglycerin, nitroglycerin patches or paste, isosorbide mononitrate or dinitrate, and even recreational amyl nitrite ("poppers"). This question comes before the dose goes anywhere near the patient.
Also review baseline blood pressure, since sildenafil is a vasodilator in its own right and can cause hypotension even without a nitrate on board. Ask about cardiac history — recent MI, unstable angina, or significant heart failure are cautions — and confirm the patient isn't on an alpha-blocker without spacing the doses, since that combination also drops blood pressure.
What to monitor
Monitor blood pressure before and after the first dose, particularly in older adults or anyone on other antihypertensives. A drop in systolic pressure is the expected pharmacologic effect at a low dose and a warning sign at a higher one.
In the PAH population, monitoring extends further: track exercise tolerance, oxygen saturation, and signs of right heart failure such as peripheral oedema or jugular venous distension, since these tell you whether the drug is achieving its therapeutic goal, not just whether it's being tolerated. Vision and hearing changes are rare but worth asking about at follow-up, since sudden vision loss or hearing loss are recognised, if uncommon, adverse effects.
Side effects versus adverse effects
Common side effects are headache, flushing, dyspepsia, and nasal congestion — all consequences of vasodilation, all generally mild, and not typically a reason to stop the drug. Patients should be told to expect these rather than be alarmed by them.
Adverse effects that need prompt reporting are different in kind: sudden vision loss or blurred vision, sudden hearing loss or ringing in the ears, and priapism — an erection lasting longer than four hours. Priapism is a urologic emergency; untreated, it risks permanent tissue damage. The line between an expected side effect and one that needs a call is really a line between discomfort and organ risk.
What to hold for and when to call
Hold sildenafil for any patient who has taken a nitrate within the required window, and hold a nitrate for any patient who has recently taken sildenafil — the interaction runs both directions. Hold for symptomatic hypotension, and hold for an unstable cardiac status where sexual activity itself would be a cardiac stressor.
Call the prescriber for an erection lasting more than four hours, for sudden vision or hearing changes, or for a blood pressure drop that doesn't resolve. In an emergency department, the practical version of this rule is simple: before nitroglycerin goes to a chest-pain patient, ask if they've taken sildenafil or a similar drug in the last day or two. That single question prevents a genuinely fatal combination.
Patient teaching
Tell the patient never to take sildenafil with any form of nitrate, and to tell every prescriber and every emergency department that they take it, because the interaction risk persists for one to two days after the last dose. This is the piece of teaching that has to stick, since the patient may not think of an ED nitroglycerin dose as related to their ED medication.
Warn them that grapefruit juice can raise sildenafil levels, that alcohol can worsen hypotension, and that an erection lasting over four hours needs emergency care, not patience. For the PAH patient, stress that the fixed dosing schedule is different from the as-needed pattern used for erectile dysfunction, and that stopping abruptly can worsen pulmonary symptoms.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our pharmacology practice questions are the closest set to what this page covers.
One question from the pharmacology set
A client with heart failure is started on furosemide 40 mg PO daily. Which findings should the nurse report to the provider before administering the next dose? Select all that apply.
Rationale
Furosemide is a loop diuretic, so the two things you are watching are potassium and kidney function. A potassium of 2.9 mEq/L is below the 3.5–5.0 reference range and puts the client at risk for dysrhythmia — hold and report. Muscle cramps with palpitations are the clinical face of that same hypokalemia, so they are reported together, not separately. A creatinine that doubles signals the diuresis has outrun renal perfusion. A blood pressure of 132/78 and a 1 kg loss are the expected response to the drug working, not reasons to hold it.
Answer: A, D, E
Common questions
Why can't sildenafil be given with nitrates?
Both cause vasodilation through the nitric oxide pathway, and together they can cause a severe, sometimes fatal drop in blood pressure. The interaction lasts 24 to 48 hours after the last sildenafil dose, so the timing question matters even when the patient isn't currently on a nitrate.
What should a nurse ask before giving nitroglycerin to a chest-pain patient?
Whether they have taken sildenafil or a similar PDE5 inhibitor in the last day or two. If they have, the nitrate is held and an alternative anti-anginal approach is used instead.
Is priapism from sildenafil an emergency?
Yes. An erection lasting longer than four hours needs immediate medical attention, since prolonged priapism risks permanent damage to penile tissue. It is not something to wait out at home.
What's the difference between sildenafil for ED and for pulmonary hypertension?
For erectile dysfunction it's taken as needed before sexual activity; for pulmonary arterial hypertension it's taken on a fixed schedule as ongoing therapy. The monitoring focus shifts accordingly, from blood pressure and priapism risk to exercise tolerance and right heart failure signs.
What are the most common sildenafil side effects a patient should expect?
Headache, flushing, dyspepsia, and nasal congestion, all related to vasodilation and usually mild. These are different from the reportable adverse effects — sudden vision or hearing loss and priapism — which need prompt medical attention.
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