Critical safety

ED pills, nitrates, and cardiac risk

The most important fact about sildenafil, tadalafil, vardenafil, and avanafil is not which one lasts longer. It is that each of them is contraindicated with nitrate medicines. The combination can drop blood pressure far enough to cause fainting, heart attack, or stroke. This page explains why, which products count as nitrates, and what “cardiac readiness” means before anyone considers a prescription.

Why the blood pressure falls

Nitrates and nitrites are nitric oxide donors. They raise cyclic GMP in the muscle of blood-vessel walls, the vessels widen, and blood pressure falls. That is useful in angina, when the goal is to reduce the heart’s workload. PDE5 inhibitors slow the breakdown of the same cyclic GMP. Used together, one drug increases the signal and the other blocks its shutdown. Clinical pharmacology studies showed that sildenafil, tadalafil, vardenafil, and avanafil each potentiate the hypotensive effect of nitrates.

On their own, these ED medicines lower blood pressure only modestly in healthy volunteers. A 100 mg sildenafil dose produced a mean maximum drop in sitting pressure of about 8/5 mm Hg. Tadalafil 20 mg produced a mean maximal supine drop of about 1.6/0.8 mm Hg relative to placebo. Those averages do not describe what happens when a nitrate is added, and they do not describe a person with unstable heart disease.

Medicines and products that count

Ask a pharmacist if you are unsure. Common nitrate and nitrite exposures include:

• Nitroglycerin tablets, sprays, ointments, pastes, and patches, including products used for anal fissure
• Isosorbide mononitrate
• Isosorbide dinitrate, including combination products
• Other organic nitrates a hospital may give, such as intravenous nitroglycerin
• Recreational nitrites sold as “poppers,” including amyl nitrite and butyl nitrite

“I only use the spray once in a while” is still a contraindication. Labels forbid nitrates taken regularly or intermittently. A single dose of a popper at a party is an intermittent nitrate.

Guanylate cyclase stimulators are a separate contraindication, not a nitrate, and they belong on the same do-not-mix list. Riociguat is used for pulmonary hypertension. Vericiguat is used in some people with heart failure. Both increase the cyclic GMP pathway. PDE5 inhibitors can deepen their blood-pressure effect.

There is no safe home schedule for mixing them

People sometimes look for a number of hours after which a nitrate would be allowed. The labels do not offer a self-managed gap. They describe, for emergency clinicians only, what to consider if a patient who already took a PDE5 inhibitor now has a life-threatening need for a nitrate.

• Sildenafil. It is unknown when nitrates can be safely administered. Levels 24 hours later are much lower than the peak in healthy volunteers (on the order of 2 ng/mL versus a peak near 440 ng/mL after 100 mg), but the label still says it is unknown whether a nitrate is safe at that point. In older adults, in liver or severe kidney disease, and with CYP3A4 inhibitors, the 24-hour level can be several times higher.
• Vardenafil. U.S. labeling states that a suitable interval for the safe administration of nitrates has not been determined.
• Tadalafil. If a nitrate is judged medically necessary in a life-threatening situation, at least 48 hours should have passed after the last dose, and the nitrate should be given only with close monitoring. An interaction with nitroglycerin was still observed at 24 hours in studies.
• Avanafil. In that same kind of life-threatening situation, the label says at least 12 hours should elapse, again only under close supervision with hemodynamic monitoring.

Those intervals are not permission to take a nitroglycerin tablet at home when the clock runs out. Chest pain after any of these drugs is an emergency. Daily tadalafil is a particular problem for emergency planning because the drug is present continuously. Anyone on the daily regimen needs every clinician, including urgent care and emergency staff, to know that.

Cardiac readiness is a clinical judgment

Sex is physical activity. A person who becomes short of breath or develops chest pain walking up a flight of stairs may not tolerate intercourse, with or without a pill. Prescribing information tells clinicians not to use these drugs when sexual activity is inadvisable because of cardiovascular status.

Tadalafil’s label goes further and lists groups who were excluded from trials and for whom tadalafil is not recommended until more is known:

• Myocardial infarction within the last 90 days
• Unstable angina, or angina during sexual intercourse
• New York Heart Association Class 2 or greater heart failure in the last 6 months
• Uncontrolled arrhythmias, hypotension below 90/50 mm Hg, or uncontrolled hypertension
• Stroke within the last 6 months

Vardenafil’s list is similar but not identical. It includes unstable angina, resting systolic pressure below 90 mm Hg, blood pressure above 170/110 mm Hg, and a recent stroke, life-threatening arrhythmia, or heart attack within 6 months, plus severe heart failure. Other PDE5 labels have their own wording. The shared point for readers is that recent heart attack, recent stroke, unstable chest pain, very low or very high blood pressure, and significant heart failure are reasons to be under cardiac care, not reasons to look for a milder ED brand.

Left ventricular outflow obstruction, including aortic stenosis and hypertrophic cardiomyopathy, makes people sensitive to vasodilators. A PDE5 inhibitor is a vasodilator.

Alpha-blockers, used for prostate symptoms and for blood pressure, are not nitrates, but they add to the pressure drop. Labels advise that the person be stable on the alpha-blocker before a PDE5 inhibitor is started, and that the PDE5 inhibitor start at its lowest recommended dose. For benign prostatic hyperplasia, tadalafil’s once-daily label says not to combine it with alpha-blockers for that use. None of this is a schedule to invent at home.

What to do in the moment

• Chest pain, fainting, or severe shortness of breath: stop sexual activity and call emergency services. Bring the medicine bottle. State the drug and the clock time.
• Do not take nitroglycerin, a nitrate spray, or a popper while an ED medicine may still be in your system.
• If you already took both, say so immediately. Emergency staff need that fact before they choose a treatment. Do not drive yourself if you feel faint.
• If a prescriber newly starts a nitrate, stop the PDE5 inhibitor and confirm the handoff. Do not keep “just in case” tablets.

What a careful prescriber is looking for

Before a first ED prescription, a competent evaluation asks about exertional chest pain, breathlessness, fainting, prior heart attack or stroke, heart failure, and blood pressure. It reviews every medicine and substance, including poppers, supplements, and drugs bought online. It is reasonable for the clinician to defer a prescription until a cardiologist has weighed in. That delay is the safety check working. A website that ships tablets after a questionnaire and never asks about nitrates is skipping the only step that prevents this interaction.

The lawful sequence is described in the prescription pathway. How hidden PDE5 inhibitors in herbal pills create the same nitrate risk is described in the supplement warning.

Sources

• Sildenafil tablets prescribing information: nitrate contraindication, unknown interval for later nitrate use, and 24-hour concentration data.
• Tadalafil tablets prescribing information: nitrate contraindication, 48-hour emergency consideration, and cardiovascular groups not recommended.
• Levitra (vardenafil) prescribing information: interval for safe nitrate use not determined; cardiovascular exclusions.
• Stendra (avanafil) prescribing information: 12-hour emergency consideration under monitoring; contraindication with guanylate cyclase stimulators.