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heightmaxxing – the erdafitinib side effect guide
introduction
most people here already know what erdafitinib is and how it can keep your growth plates open longer.
this thread isn't about that.
i'm breaking down the most common side effects from taking it and how to manage or avoid them entirely.
side effects at 8mg daily
listed from most to least common: elevated phosphate levels, nail issues, stomatitis, diarrhea, raised creatinine, increased alkaline phosphatase, elevated alt, low hemoglobin, low sodium, raised ast, fatigue, dry mouth, dry skin, low phosphate, appetite loss, taste changes, constipation, high calcium, dry eyes, palmar plantar erythrodysesthesia, high potassium, hair loss, central serous retinopathy, and painful skin lesions.
(pmid: 37757826)
pre cycle checklist
1. check phosphate levels two weeks into therapy, then monthly after that. keep it under 7.2 mg/dl.
2. get an eye exam in the first few months including vision and intraocular pressure checks.
3. run a full blood panel before starting and again after you begin.
4. track alt, ast, creatinine, and bilirubin consistently. or just skip the hassle and get on sevelamer.
phosphate levels and what to do
7 to 8.99 mg/dl
keep going at the same dose, add a phosphate binder with meals until levels drop below 7.
9 to 10 mg/dl
lower the dose if phosphate stays above 7 for two months or if clinically indicated.
above 10 mg/dl
pause treatment and reassess weekly until phosphate drops under 7, then restart at the same dose.
introduce a phosphate binder with food until levels normalize.
reduce dose if phosphate stays at or above 9 for a month or if clinically necessary.
pause treatment with weekly check ins until phosphate is under 7, then restart at the same dose.
if phosphate stays above 10 for more than two weeks, stop permanently.
only use medical management when clinically relevant.
hyperphosphatemia and soft tissue calcification
fgfr inhibition causes phosphate buildup in the blood.
this leads to calcification of soft tissues, skin calcification, nonuremic calciphylaxis, and vascular calcification.
not something to ignore.
keeping phosphate in check
keep daily phosphate intake under 600 to 800 mg while on this compound.
avoid anything that raises phosphate levels during the first two weeks.
if your phosphate goes above 7.2 mg/dl, bring in sevelamer to bring it back down to baseline or under 7.2 before you even think about lowering your erdafitinib dose.
dry eyes and retinal issues
to avoid dry eyes, use lubricating drops or gels consistently.
apply them at least every two hours during the day.
erdafitinib can also cause retinal pigment epithelium detachment, which affects your vision.
if that happens, fall back on the same protocol i laid out for dry eyes and hyperphosphatemia.
kidney and liver concerns
there's not much data on how erdafitinib behaves in people with kidney issues or moderate to severe liver impairment.
but from what i've gathered, it binds to alpha 1 acid glycoprotein, which actually lowers the risk of toxicity.
so if you have pre existing liver or kidney problems, the side effect profile might be worse.
(pmid: 31602692)
introduction
most people here already know what erdafitinib is and how it can keep your growth plates open longer.
this thread isn't about that.
i'm breaking down the most common side effects from taking it and how to manage or avoid them entirely.
side effects at 8mg daily
listed from most to least common: elevated phosphate levels, nail issues, stomatitis, diarrhea, raised creatinine, increased alkaline phosphatase, elevated alt, low hemoglobin, low sodium, raised ast, fatigue, dry mouth, dry skin, low phosphate, appetite loss, taste changes, constipation, high calcium, dry eyes, palmar plantar erythrodysesthesia, high potassium, hair loss, central serous retinopathy, and painful skin lesions.
(pmid: 37757826)
pre cycle checklist
1. check phosphate levels two weeks into therapy, then monthly after that. keep it under 7.2 mg/dl.
2. get an eye exam in the first few months including vision and intraocular pressure checks.
3. run a full blood panel before starting and again after you begin.
4. track alt, ast, creatinine, and bilirubin consistently. or just skip the hassle and get on sevelamer.
phosphate levels and what to do
7 to 8.99 mg/dl
keep going at the same dose, add a phosphate binder with meals until levels drop below 7.
9 to 10 mg/dl
lower the dose if phosphate stays above 7 for two months or if clinically indicated.
above 10 mg/dl
pause treatment and reassess weekly until phosphate drops under 7, then restart at the same dose.
introduce a phosphate binder with food until levels normalize.
reduce dose if phosphate stays at or above 9 for a month or if clinically necessary.
pause treatment with weekly check ins until phosphate is under 7, then restart at the same dose.
if phosphate stays above 10 for more than two weeks, stop permanently.
only use medical management when clinically relevant.
hyperphosphatemia and soft tissue calcification
fgfr inhibition causes phosphate buildup in the blood.
this leads to calcification of soft tissues, skin calcification, nonuremic calciphylaxis, and vascular calcification.
not something to ignore.
keeping phosphate in check
keep daily phosphate intake under 600 to 800 mg while on this compound.
avoid anything that raises phosphate levels during the first two weeks.
if your phosphate goes above 7.2 mg/dl, bring in sevelamer to bring it back down to baseline or under 7.2 before you even think about lowering your erdafitinib dose.
dry eyes and retinal issues
to avoid dry eyes, use lubricating drops or gels consistently.
apply them at least every two hours during the day.
erdafitinib can also cause retinal pigment epithelium detachment, which affects your vision.
if that happens, fall back on the same protocol i laid out for dry eyes and hyperphosphatemia.
kidney and liver concerns
there's not much data on how erdafitinib behaves in people with kidney issues or moderate to severe liver impairment.
but from what i've gathered, it binds to alpha 1 acid glycoprotein, which actually lowers the risk of toxicity.
so if you have pre existing liver or kidney problems, the side effect profile might be worse.
(pmid: 31602692)
