Switching Off Sildenafil: Riociguat Against a Borderline Kidney
Her PAH isn't responding to sildenafil, and the drug shown to help in exactly this situation cannot be given alongside it. The question is whether her kidneys make the switch itself riskier than staying inadequately treated.
L.K., a 55-year-old woman, has worked as a hospice chaplain for nearly two decades, sitting with families through exactly the kind of uncertainty she is now living on the other side of the conversation. Her adult daughter moved back home this year after a divorce, and between the two of them the house has felt fuller than it has in a long time — which is part of why L.K. has been slower than she might otherwise be to admit how much her own walking distance has shrunk. She was diagnosed with idiopathic pulmonary arterial hypertension three years ago and has been on combination therapy with sildenafil and ambrisentan since, alongside a decade-old diagnosis of hypertension that has left her with stage 3b chronic kidney disease, eGFR 38.
Her most recent 6MWD is down from 380 to 310 meters over the past six months, her WHO functional class has slipped to III, and her NT-proBNP has been climbing on serial labs — three independent signals converging on the same conclusion, that her current regimen has stopped being adequate. RESPITE reported improvement in 6MWD, functional class, NT-proBNP, and hemodynamics when inadequate PDE5-inhibitor responders were switched directly to riociguat, and her presentation matches that trial's population closely — though RESPITE was a single-arm, open-label study of 61 patients, not a randomized comparison. What that trial doesn't resolve for her specifically is what her borderline renal function does to the switch: riociguat is partly renally cleared, and hypotension risk from guanylate-cyclase stimulation is amplified when clearance is already reduced, while sildenafil and riociguat cannot be given together under any circumstances — coadministration is a hard contraindication because of the same hypotension risk. Staying on an inadequate regimen and switching to a genuinely better-evidenced one that carries more risk specifically for her kidneys are not clean alternatives.
At the PAH clinic follow-up
This is textbook RESPITE: WHO FC III, declining 6MWD, rising NT-proBNP despite an adequate PDE5-inhibitor trial. Switching to riociguat improved all three of those endpoints in that trial's population, plus measured hemodynamics. I'd start the sildenafil washout and begin riociguat titration.
I agree the evidence supports switching in principle, but her eGFR of 38 changes the risk calculus on the drug itself, not just on whether to switch. Riociguat is partly renally cleared, and the hypotension risk that's already the reason PDE5 inhibitors and riociguat can never be combined is amplified when clearance is reduced.
That's an argument for starting low and titrating slowly with real monitoring, not an argument against switching at all — I want to be clear I'm not proposing we leave her on a regimen that's already failing her.
Agreed on both counts. Sildenafil discontinued with a 24-hour washout before the first riociguat dose — not 48, since tadalafil requires the longer window and she's on sildenafil. Riociguat starting at 0.5 mg three times daily — the label’s reduced start for patients who may not tolerate the hypotensive effect, rather than the standard 1 mg three times daily — titrating in 0.5 mg increments no sooner than every two weeks toward the 2.5 mg maximum, with blood pressure and renal function checked at each step. I'd hold off on layering in a prostacyclin-pathway agent until we see whether the switch itself gets her back toward her prior functional class.
Sildenafil discontinued with a 24-hour washout; riociguat started at 0.5 mg three times daily — the label’s reduced starting dose, not the standard 1 mg — with a conservative titration schedule, blood pressure and renal function rechecked at each dose increase. Ambrisentan continued unchanged.
Not yet known, and stated as the explicit branch point for her 4-week follow-up:
The switch proceeds as RESPITE would predict, with functional class and 6MWD reassessed at 3 months.
Riociguat is held at a sub-target dose or reconsidered, and prostacyclin-pathway escalation on top of unchanged PDE5-inhibitor therapy becomes the alternate path.