I missed it two months ago for a variety of reasons, but as of the first week of July, I’d been on burosumab for nine years.
Ninth is a kind of odd anniversary—substantial, so it’s hard now for anyone to credibly say we don’t know what the medium-term risks/benefits are (minor risks, major benefits)—but not quite the magical tenth year, which ought to be enough for clinicians to stop being so fast to say, “Well, sure, burosumab is good in the first year or two, but maybe there are surprise negatives over the longer term.” There will still be some of that until patients have spent an entire lifetime on burosumab, but ten years ought to silence all but the most severe critics (and the bad-faith critics).
I expect there to be a flurry of articles in mid-late 2027 (because of the delay in publishing) based on the ten years of data that, by the end of 2026, will have been collected in the Disease Monitoring Program (still loathe that term) in the U.S., and similar work in other countries. Until then, we just have anecdotal data, so here’s mine.
According to the Crysvita label, the potential serious side-effects for adults are: “back pain, headache, tooth infection, restless leg syndrome, vitamin D decreased, dizziness, constipation, blood phosphorus increased.”
It’s kinda’ hard to take the last one seriously — of course the phos increased; that’s the whole point of treatment! I suppose it’s a reminder to clinicians to make sure the levels don’t get too high, but that was never an issue for me. As to the rest, I’ve had back pain and headaches, but for the most part, they pre-existed treatment, and I’ve had less of both (with one exception discussed below) since beginning treatment. I have not experienced any significant restless leg syndrome (maybe some minor episodes, but not enough to seek treatment for it), and my vitamin D has been normal throughout treatment. Any dizziness or constipation has been due to other causes.
I’m not sure why they don’t mention injection site irritation for adults, since it’s a listed side-effect for pediatric patients, and I believe some adults experience it too. In any event, I’ve had no such irritation, and in fact have trained the nurse doing the injections NOT to apply a bandage after the injection, because I never need it.
The one side-effect I did have briefly, and I believe it may be fairly common but not discussed much, is increased back pain/spasms while my body adjusted to the luxury of adequate phosphorus. My pain/spasms only lasted less than a month, but I’ve heard of others who had an increase of pain for six to twelve months before their bodies finally adjusted to the increase in phosphorus levels. In my case, the principal investigator speculated that the increased back pain and spasms was a matter of my muscles finally having enough energy to work properly, and in the course of relearning their role, put some unexpected pressure on the spine. (Adenosine triphosphate, ATP, fuels muscles, and as the name suggests, requires phosphorus.)
So, what about the benefits? It’s a little hard to explain, because what burosumab does is basically make us “normal,” in terms of our phosphorus metabolism. It’s not like, say, some Star Trek style treatment where one minute you have a broken arm and they wave a gizmo over it, and your arm is healed. It’s a much more gradual process, as bones and muscles and teeth that have been begging for phosphorus finally have enough. The bones get stuffed with phosphorus finally, and the body produces enough ATP to give us more energy (and less fatigue), and our muscles start working properly to support the spine, etc.
In my case, bone pain melted away gradually, as did my spinal spasms. We tend to forget about pain once it’s gone—we know we had pain, we know it was bad, but we can’t recreate it the way (some of us) can recreate a mental image of something we once saw—so as I improved, I didn’t really notice the change on a day-to-day basis. Absence of pain just becomes “normal” rather than something to pay attention to.
There were only two situations where I really noticed the improvement. One was when I had a setback, like a delay in a dose, or when I lost a lot of phosphorus during surgery, and the bone pain came back, and I’d think, “oh, yeah, this is how I used to feel all the time.” For the most part though, the improvement became my new normal, and I didn’t notice it. The second situation was when I was expecting to hurt or have a spasm, and I didn’t. Before treatment, I had briefly-paralyzing back spasms almost daily, and sometimes multiple times daily, whenever my spine was jarred or twisted. It was about eighteen months after I started treatment when I hit a pothole unexpectedly, and had just enough time to brace myself mentally for the pain/spasm, before I realized that, no, it didn’t hurt at all. And then I realized that I couldn’t remember the last time I’d had a spinal spasm. Not having them had become my new normal, so I just didn’t notice it.
Similarly, I didn’t notice the increase in energy and corresponding drop in fatigue, largely because I automatically adjusted my activity level to match the improved energy/alertness. I didn’t so much feel more energetic and alert, as I found I was able to do more before I had to stop due to fatigue or depleted energy.
Finally, my experience is complicated by the effects of aging. I’m not the oldest person in the clinical trial, but I’m ONE of the oldest. All sorts of permanent damage happened before I started treatment, so I went into the trial with the main goal of slowing the progression. That goal was definitely achieved—my enthesopathy was worsening at a noticeable rate, and I was anticipating needing a wheelchair within a year or two, and it has not progressed noticeably in the nine years of treatment—so the additional benefits of the spasms stopping, plus more energy and less fatigue were a nice bonus.
Aging did catch up with me eventually though. For the first six or seven years, I felt like I was aging backwards, feeling better and doing more than I had ten years earlier. In the last year or two, the effects of aging seem to have outpaced the benefits of treatment, so I’m plateauing, rather than feeling better each year. But with a progressive disorder, as long as I’m not getting worse, that’s a big benefit!
Bottom line: Over the course of nine years on burosumab, I’ve had no ongoing side-effects. The benefits, while substantial, are hard to quantify because of 1) how gradual they were, 2) the way we adjust to a new normal, and 3) the complication of the adverse effects of aging working against the benefits.
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Please note that the author is a well-read patient, not a doctor, and is not offering medical or legal advice.
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