Sickle Cell Disease After Hydroxyurea: One Escalation Drug Gone, the Other Unconfirmed
A single patient, still crisis-prone despite optimized hydroxyurea. The disagreement isn't the usual escalation menu — one of the two drugs that menu used to include is gone entirely, and the other is still prescribable on a confirmatory trial that missed.
Marcus T. joined a Sunday-league soccer team two years ago, playing center-back, mostly so his vaso-occlusive crises wouldn't be the only thing organizing his calendar — a small act of defiance he's kept up even through a season he had to sit out entirely. He is two semesters from finishing his electrician's apprenticeship. He has HbSS sickle cell disease and has been on hydroxyurea at his maximum tolerated dose — 32 mg/kg/day, limited by mild, reproducible neutropenia at higher doses — for three years, with a documented HbF response that never climbed past 14 percent despite good, confirmed adherence tracked through pharmacy refill records.
He has still had five emergency department visits for vaso-occlusive crisis in the past year, two requiring admission for pain unresponsive to his home regimen, and missed enough apprenticeship hours after the last one that his program director asked directly whether he needs a different plan. His most recent admission required patient-controlled IV opioid analgesia for four days, longer than any prior crisis, which is part of what brought this conversation forward rather than waiting for his next scheduled visit.
Two years ago this conversation would have run differently. Voxelotor, a polymerization inhibitor that raised hemoglobin in HOPE, was withdrawn from worldwide markets by Pfizer in September 2024 after post-marketing data showed an imbalance in vaso-occlusive crises and deaths that its benefit no longer outweighed. Crizanlizumab is the more complicated case: it cut the annual crisis rate by roughly 45 percent in the phase 2 SUSTAIN trial, but its confirmatory phase 3 STAND trial found no separation from placebo, and while the European Commission revoked its authorization in August 2023 and the UK's MHRA followed in January 2024, it remains FDA-approved and prescribable here. So one of Marcus's two escalation options no longer exists and the other legally does, resting on a confirmatory trial that missed. The harder question is not whether he can have crizanlizumab — it is whether a drug whose own confirmatory trial failed to reproduce its benefit is what five emergency visits should be answered with.
One option gone, one option unconfirmed
Voxelotor is simply gone, so that branch closes itself. Crizanlizumab I could still write for today, and I don't think I should: STAND was the trial built to confirm SUSTAIN's benefit and it found no difference from placebo in annualized crises, which is why Europe and the UK revoked it. An available drug and a drug shown to work are not the same claim. Before reaching for it anyway, I'd confirm hydroxyurea is genuinely optimized rather than treating three years at his current dose as the ceiling — pharmacogenomic-guided titration against his actual MCV and absolute neutrophil count trend, not just the dose number, sometimes finds real room upward.
This isn't a confident bet that it will work — a flat HbF response after three years at a stable dose is a real signal he may be a genuine partial responder, not an undertreated one. But it's an option resting on his own pharmacology rather than on a trial that already failed.
I'd push back a little on writing crizanlizumab off that cleanly. STAND was negative, and I'm not arguing it wasn't — but a failed confirmatory trial in a broad enrolled population isn't the same finding as harm, and the FDA has left it approved on exactly that reading. That said, I wouldn't reach for it here either, and my reason is his: he needs something that works on a timescale his admissions are already outrunning. A chronic transfusion program, even a modest simple-transfusion schedule rather than full exchange, reliably cuts vaso-occlusive frequency by diluting HbS-containing cells, and it doesn't depend on how the crizanlizumab evidence eventually settles.
The real cost is iron overload with long-term simple transfusion, which argues for building chelation into the plan from the start rather than treating it as a later problem, and for revisiting exchange transfusion if his ferritin trends up faster than expected.
Both of those are reasonable near-term moves, and I don't think they're actually in conflict — optimize hydroxyurea while starting the transfusion conversation, rather than sequence them. What I'd add is that his profile — young, no alloimmunization yet, no organ damage — is exactly the profile that makes early referral for curative-intent gene therapy evaluation worth starting now, not after a transfusion program has had years to build alloimmunization risk against it.
Agreed: hydroxyurea dose reassessment via pharmacogenomic-guided titration, a chronic simple transfusion program started in parallel rather than held in reserve, and an urgent referral for curative-intent gene therapy evaluation given his age and unalloimmunized status.
Not agreed: how aggressively to pursue exchange transfusion versus simple transfusion as the starting modality — left as a decision for the transfusion medicine team once his baseline iron studies and crisis trajectory over the next two months are in hand. Also unsettled, and deliberately left on the record rather than resolved: whether crizanlizumab's continued FDA approval after a negative confirmatory trial means it retains a place for patients out of other options, or means only that withdrawal decisions lag the evidence.