Viagra and Imaging Contrast Dye: What You Need to Know Before Your Scan

Does sildenafil interact with contrast dye?

The Viagra label's drug interactions section lists nitrates, alpha-blockers, amlodipine, ritonavir and other strong CYP3A4 inhibitors, and alcohol [1]. Contrast media are not among them [1].

Sildenafil inhibits PDE5, the enzyme that breaks down cyclic GMP, and this enhances nitric oxide-driven smooth muscle relaxation [1]. The label's cautions are mainly about other drugs that also lower blood pressure.

What the label warns about that can matter on scan day

A single 100 mg dose lowered supine blood pressure in healthy volunteers by a mean maximum of about 8.4/5.5 mm Hg, and the fall was not dose-related between 25 and 100 mg [1].

Alpha-blockers such as doxazosin and tamsulosin add to that fall. In a doxazosin study, Viagra 25 mg produced a placebo-subtracted maximum standing systolic fall of 6.0 mm Hg (7.4 mm Hg supine), and one of the four men given 100 mg had severe postural hypotension [1]. The label says patients should be stable on the alpha-blocker before starting Viagra and should start at 25 mg [1].

Amlodipine: Viagra 100 mg with amlodipine 5 or 10 mg in hypertensive patients gave an additional mean supine fall of 8/7 mm Hg [1].

Nitrates: use of organic nitrates or nitrites in any form, regular or intermittent, is contraindicated with Viagra [1]. After a dose it is unknown when nitrates can be safely given; sildenafil levels 24 hours after 100 mg are about 2 ng/mL against a peak of about 440 ng/mL, but are 3 to 8 times higher in men over 65, in liver or severe kidney impairment, or with erythromycin or a strong CYP3A4 inhibitor [1]. The label states it is unknown whether nitrates are safe even at 24 hours [1]. Riociguat, a guanylate cyclase stimulator, is also contraindicated [1].

Contrast-induced kidney injury: does sildenafil change the risk?

With gadolinium, the kidney concern is nephrogenic systemic fibrosis, reported in advanced kidney disease and more likely with larger or repeated doses and with non-ionic linear chelates; no clearly effective treatment exists [3]. Contrast-induced nephropathy after angiography and cardiac interventions is a separate, well-described problem [2]. The Viagra label does not link sildenafil to either condition [1].

Sildenafil exposure itself does change with kidney and liver function: AUC is about doubled in severe renal impairment (creatinine clearance below 30 mL/min) and about 85% higher in Child-Pugh A/B hepatic impairment, and the label suggests a 25 mg starting dose in both [1]. In healthy men aged 65 or older, AUC was about 84% higher for sildenafil and 107% higher for its active metabolite [1].

Does the label give a hold time before a contrast scan?

Nothing in the Viagra label's dosing or drug interactions sections sets an interval between a sildenafil dose and contrast imaging [1]. The only timing statement the label makes concerns nitrates: after Viagra has been taken, it is unknown when nitrates can be safely given [1]. Sildenafil reaches peak blood levels 30 to 120 minutes after a fasting dose and has a terminal half-life of about 4 hours, shared by its active metabolite [1].

If the scan might involve nitroglycerin

If a procedure involves a nitrate in any form, the Viagra contraindication applies [1].