Both cheap both promising but one is glazed over the other
(Red for important stuff green for basic knowledge)
LONG THREAD
Infigratinib vs. erdafitinib: a deeper evidence review
the first thing to recognize is these 2 drugs have produced growth signals in very different populations. Infigratinhib has been primarily studied as a treatment for children with achondroplesia and is currently in stage 3 clinical trials. But in contrast the striking erdafitinhib observations arose as a side effect
incidentally in pediatric oncology patients without skeletal dysplasia, in one case a child grew 14.3 cm( 5.5 inches) in just 9 months. these children were given erda to treat fgfr altered tumors but also got a lot taller.
This distinction is crucial. Infigs evidence asks if suppressing excessive fgfr3 signaling can correct impaired skeletal growth, whereas erda unexpectedly asks What happens to an otherwise growing human skeleton when systemic FGFR signaling is strongly inhibited.
Infigratinib’s human evidence is much more systematic.
The infig evidence has progressed through a rather conventional developmental pathway.
PROPEL/PROPEL 2 studied children with achondroplasia, and the phase-2 study enrolled 72 children aged 3–11 years across five dose cohorts: 0.016, 0.032, 0.064, 0.128, and 0.25 mg/kg/day. At the highest cohort, the average improvement in annualized height velocity from baseline of 18 months was around 2.5 cm/year, with a .54 z score improvement in height a score relative to achondroplesia reference population
More importantly this has now progressed to randomized phase 3 evidence. In these trials 114 children with achondroplesia were randomized to infig or a placebo,
At 52 weeks, the least-squares mean difference in annualized height velocity was 1.74 cm/year in favor of infigratinib, with a 95% CI of 1.31–2.17 cm/year. Height z-score also improved by 0.32 relative to placebo
although 1.7 cm may sound small it provides enormous evidence for infig when evidence ranking. We have controlled prospective pediatric height measurements rather than just an unexpected effect found retrospectively
There is a major caveat here, these children (ages 3-18) had achondroplesia, they weren’t healthy children looking to go from 50th perceive to 90th percentile height like us.
So we can’t apply this 1.74+ cm/year to an healthy child. Fgfr3 signaling is already pathologically elevated in kids with achondroplesia, meaning the drug lifts an abnormal break which we all have but not as severe as they do.
Quick definitions so you don’t get lost
(Lower number = more inhibition)
Infigratinib: FGFR1 ~0.9 nM, FGFR2 ~1.4 nM, FGFR3 ~1.0 nM, FGFR4 ~60 nM → FGFR1 ≈ FGFR3 ≈ FGFR2 >>> FGFR4
Erdafitinib: FGFR1 ~1.2 nM, FGFR2 ~2.5 nM, FGFR3 ~3 nM, FGFR4 ~5.7 nM → FGFR1 > FGFR2 > FGFR3 > FGFR4, but all are strongly inhibited
The animal data supports that point.
Infig has consistently produced strong effects in fgfr3 driven mouse models.
In one achondroplasia model, infigratinib increased long-bone dimensions substantially. A published comparison reported increases relative to vehicle of approximately 10.4% for femur and 16.8% for tibia at the relevant experimental regimen.
newer mouse study is particularly informative because it compared achondroplasia and hypochondroplasia. In the hypochondroplasia model, daily infigratinib produced roughly 3.2% femur and 3.2% tibia increases over 21 days, substantially smaller than the effects previously observed in the more severe achondroplasia model
That gives us an important biological gradient:
more pathological FGFR3 signaling → greater apparent response to FGFR inhibition.
That doesn’t mean a normal skeleton would show zero response. It means that the magnitude should not automatically be extrapolated from achondroplasia.
But this is where erdafitinhib gets really interesting.
Erda provides evidence that the story is not just FGFR3 inhibition only works when FGFR3 is mutated and hyperactive.
A published pediatric case involved a prepubescent boy without a skeletal dysplasia who received erdafitinib for an FGFR1-altered tumor. He grew 14.3 cm over nine months, corresponding to an annualized rate of approximately 19.1 cm/year, compared with roughly 10 cm/year expected for a 15-year-old boy. His height percentile shifted from approximately the 16th–25th percentile to around the 70th percentile.
(Growing from around 5’5.5 to 5’11 in 9 mths compares to an expected of 5’5.5 to 5’9.5 in a full year.)
This is an extraordinary large raw signal.
And it wasn’t just the child entering puberty,
The researchers observed skeletal overgrowth and spinal deformity, including cervical lordosis and thoracic scoliosis, and the changes were sufficiently serious that surgical correction was eventually required.
This highly suggests the growth came from the fgfr3 inhibition, and remember this was a child who has normal fgfr3 levels.
So erdafitinib gives us something infigratinib doesn’t
direct evidence that pharmacological FGFR inhibition can produce very large skeletal-growth effects in a child without achondroplasia.
This effect wasn’t seen in just one case
Another report reviewed two patients without skeletal dysplasia who experienced an acceleration in growth during erdinfitinhib treatment.
The particularly interesting aspect was that the growth acceleration occurred despite the absence of the usual endocrine explanation.
In one patient, testosterone remained extremely low and there was no evidence of pubertal progression. In the other, the patient remained Tanner stage 1 with very low estradiol and very low IGF-1. Yet growth accelerated after erdafitinib began.
In one patient, growth acceleration occurred despite stable GH dosing and without an increase in IGF-1; in the other, IGF-1 was profoundly low. The authors therefore proposed that the phenomenon represented an FGFR-related, growthfactor and sex steroid independent mechanism.
This is extremely important for the biology.
It means:
FGFR inhibition → increased skeletal growth
cannot simply be reduced to:
FGFR inhibition → higher GH/IGF-1 → growth.
There appears to be a local growth-plate mechanism.
The growth plate itself provides the explanation
FGFR3 is normally expressed in growth-plate chondrocytes and acts partly as a negative regulator of endochondral bone growth.
That means the normal growth plate isn’t operating with FGFR3 completely absent. Instead, there is a balance:
pro-growth signals
versus
anti-growth/feedback signals.
FGFR3 contributes to the latter.
So inhibiting FGFR3 can theoretically shift the equilibrium toward:
chondrocyte proliferation → hypertrophy → matrix production → ossification → longitudinal expansion.
That is why the erdafitinib observations are not biologically impossible or contradictory.
In fact, there is genetic evidence pointing in the same direction: loss-of-function FGFR3 variants in humans and animals are associated with skeletal overgrowth, and the erdafitinib authors specifically discuss the similarity between pharmacological FGFR inhibition and FGFR3 loss-of-function states
TYRA-300 makes the comparison even more interesting
Tyra-300 is another fgfr3 inhibitor, it is the most selective and expensive costing up to 1500 a month for meaningful doses
TYRA-300 provides perhaps the cleanest experimental demonstration that normal FGFR3 signaling itself can restrain growth.
Researchers deliberately administered TYRA-300 to wild-type mice from four to eight weeks of age, rather than restricting the experiment to FGFR3-mutant animals(meaning these mice were normal)
At 14 mg/kg/day, nasoanal length increased by 7.3%, while tibia and femur length also increased significantly.
That is extremely important because it establishes:
FGFR3 inhibition can increase skeletal growth even when FGFR3 is not pathologically activated.
However, the response was still generally larger in the FGFR3-driven disease models. TYRA-300 produced particularly strong effects in achondroplasia-model mice, while the hypochondroplasia model showed smaller responses because the underlying phenotype is milder.
So the emerging picture isn’t:
normal = zero response
but rather:
pathological FGFR3 activation = larger available therapeutic effect
normal FGFR3 = potentially smaller but biologically real effect.
“Erda has way better numbers so it has to be better overall”
No, and this is very important don’t skip here
The ~19 cm/year growth observation with erdafitinib is not equivalent to a 19 cm/year healthy-growth treatment effect.
The skeleton was behaving abnormally.
The patient developed:
The other report found growth-plate widening and profound metaphyseal sclerosis/mineralization changes shortly after treatment began.
There is also a published series describing slipped capital femoral epiphysis (SCFE) associated with pediatric FGFR-TKI exposure, with growth-plate widening and altered mineralization considered important contributing factors.
So erdafitinib demonstrates maximum biological disruption, not necessarily maximum desirable growth.
Why infigratinib may actually be the better “growth” experiment
Infigratinib’s effect is much less spectacular numerically, but that’s partly because its clinical program was designed around correcting pathological FGFR3 signaling rather than producing uncontrolled skeletal overgrowth.
The phase-3 result:
+1.74 cm/year vs placebo
is therefore a much cleaner measurement of a sustained therapeutic effect than a case report showing ~19 cm/year accompanied by skeletal deformity.
And its animal studies demonstrate reproducible correction of:
in FGFR3-driven models.
So if the endpoint
“How much can I disrupt skeletal growth?”
erdafitinib wins the available human anecdotal evidence.
If the endpoint is:
“How convincingly can we demonstrate controlled improvement of longitudinal growth?”
infigratinib has the much stronger evidence base.
basically erda=more disruption, less safe, better numbers
Infig= bit more selective so less disruption, more clinical evidence of growth, lower numbers
“Infig inhibits fgfr3 more and is more selective than erda, why are its numbers supposedly worse?”
Erdafitinib’s broader profile may help explain why its skeletal effects can look disproportionately strong despite having weaker FGFR3 potency than infigratinib: FGFR1, FGFR2, FGFR3 and FGFR4 are not interchangeable, and all participate in skeletal development and growth-plate regulation. FGFR3 is the clearest growth-plate brake, particularly in proliferative and prehypertrophic chondrocytes, whereas FGFR1 is more prominent in prehypertrophic/hypertrophic chondrocytes and is involved in differentiation; FGFR2 has important roles earlier in chondrogenesis and osteoblast development, while FGFR4 is expressed in resting/proliferative zones and has more context-dependent functions. Thus, infigratinib’s ~1 nM FGFR3 potency does not mean it produces the largest total skeletal perturbation: it strongly inhibits FGFR1–3 but largely spares FGFR4, whereas erdafitinib inhibits all four in the low-nanomolar range (FGFR1 ~1.2, FGFR2 ~2.5, FGFR3 ~3.0, FGFR4 ~5.7 nM). A broader blockade could therefore alter several interacting regulatory compartments simultaneously, potentially producing a larger overall phenotype even with weaker FGFR3 inhibition
Conclusion, what mogs infig or erda?
it depends on what you’re looking for
Infigratinib does not “mog” erdafitinib in raw growth magnitude. Erdafitinib’s accidental pediatric growth phenotype is considerably more dramatic.
But infigratinib absolutely mogs erdafitinib in evidentiary quality for controlled growth promotion: prospective trials, a defined population, a comparator group, reproducible animal data, quantified height velocity, and a coherent therapeutic rationale.
If you’re broke do erda or infig, if you have more money do hgh (8 iu minimum) paired with erda or infig. If you’re rich do high hgh and experiment with ky or Tyra.
More experimental things like sag21k, Ap-811, foxo4-dri or even epitalon on are hard to obtain and have little clinical evidence so process with caution
Sources
Sources
Sources
Sources
Sources
Sources
Sources
(Red for important stuff green for basic knowledge)
LONG THREAD
Infigratinib vs. erdafitinib: a deeper evidence review
the first thing to recognize is these 2 drugs have produced growth signals in very different populations. Infigratinhib has been primarily studied as a treatment for children with achondroplesia and is currently in stage 3 clinical trials. But in contrast the striking erdafitinhib observations arose as a side effect
incidentally in pediatric oncology patients without skeletal dysplasia, in one case a child grew 14.3 cm( 5.5 inches) in just 9 months. these children were given erda to treat fgfr altered tumors but also got a lot taller.
This distinction is crucial. Infigs evidence asks if suppressing excessive fgfr3 signaling can correct impaired skeletal growth, whereas erda unexpectedly asks What happens to an otherwise growing human skeleton when systemic FGFR signaling is strongly inhibited.
Infigratinib’s human evidence is much more systematic.
The infig evidence has progressed through a rather conventional developmental pathway.
PROPEL/PROPEL 2 studied children with achondroplasia, and the phase-2 study enrolled 72 children aged 3–11 years across five dose cohorts: 0.016, 0.032, 0.064, 0.128, and 0.25 mg/kg/day. At the highest cohort, the average improvement in annualized height velocity from baseline of 18 months was around 2.5 cm/year, with a .54 z score improvement in height a score relative to achondroplesia reference population
More importantly this has now progressed to randomized phase 3 evidence. In these trials 114 children with achondroplesia were randomized to infig or a placebo,
At 52 weeks, the least-squares mean difference in annualized height velocity was 1.74 cm/year in favor of infigratinib, with a 95% CI of 1.31–2.17 cm/year. Height z-score also improved by 0.32 relative to placebo
although 1.7 cm may sound small it provides enormous evidence for infig when evidence ranking. We have controlled prospective pediatric height measurements rather than just an unexpected effect found retrospectively
There is a major caveat here, these children (ages 3-18) had achondroplesia, they weren’t healthy children looking to go from 50th perceive to 90th percentile height like us.
So we can’t apply this 1.74+ cm/year to an healthy child. Fgfr3 signaling is already pathologically elevated in kids with achondroplesia, meaning the drug lifts an abnormal break which we all have but not as severe as they do.
Quick definitions so you don’t get lost
- Infigratinib: FGFR1–3 inhibitor, especially FGFR3; reduces excessive FGFR3 signaling.
- Erdafitinib: broader FGFR1–4 inhibitor, including FGFR3; less selective.
(Lower number = more inhibition)
Infigratinib: FGFR1 ~0.9 nM, FGFR2 ~1.4 nM, FGFR3 ~1.0 nM, FGFR4 ~60 nM → FGFR1 ≈ FGFR3 ≈ FGFR2 >>> FGFR4
Erdafitinib: FGFR1 ~1.2 nM, FGFR2 ~2.5 nM, FGFR3 ~3 nM, FGFR4 ~5.7 nM → FGFR1 > FGFR2 > FGFR3 > FGFR4, but all are strongly inhibited
- Achondroplasia (ACH): severe skeletal dysplasia caused by activating FGFR3 mutations, strongly suppressing endochondral bone growth.
- Hypochondroplasia (HCH): milder FGFR3-related skeletal dysplasia with less severe FGFR3 overactivity.
The animal data supports that point.
Infig has consistently produced strong effects in fgfr3 driven mouse models.
In one achondroplasia model, infigratinib increased long-bone dimensions substantially. A published comparison reported increases relative to vehicle of approximately 10.4% for femur and 16.8% for tibia at the relevant experimental regimen.
newer mouse study is particularly informative because it compared achondroplasia and hypochondroplasia. In the hypochondroplasia model, daily infigratinib produced roughly 3.2% femur and 3.2% tibia increases over 21 days, substantially smaller than the effects previously observed in the more severe achondroplasia model
That gives us an important biological gradient:
more pathological FGFR3 signaling → greater apparent response to FGFR inhibition.
That doesn’t mean a normal skeleton would show zero response. It means that the magnitude should not automatically be extrapolated from achondroplasia.
But this is where erdafitinhib gets really interesting.
Erda provides evidence that the story is not just FGFR3 inhibition only works when FGFR3 is mutated and hyperactive.
A published pediatric case involved a prepubescent boy without a skeletal dysplasia who received erdafitinib for an FGFR1-altered tumor. He grew 14.3 cm over nine months, corresponding to an annualized rate of approximately 19.1 cm/year, compared with roughly 10 cm/year expected for a 15-year-old boy. His height percentile shifted from approximately the 16th–25th percentile to around the 70th percentile.
(Growing from around 5’5.5 to 5’11 in 9 mths compares to an expected of 5’5.5 to 5’9.5 in a full year.)
This is an extraordinary large raw signal.
And it wasn’t just the child entering puberty,
The researchers observed skeletal overgrowth and spinal deformity, including cervical lordosis and thoracic scoliosis, and the changes were sufficiently serious that surgical correction was eventually required.
This highly suggests the growth came from the fgfr3 inhibition, and remember this was a child who has normal fgfr3 levels.
So erdafitinib gives us something infigratinib doesn’t
direct evidence that pharmacological FGFR inhibition can produce very large skeletal-growth effects in a child without achondroplasia.
This effect wasn’t seen in just one case
Another report reviewed two patients without skeletal dysplasia who experienced an acceleration in growth during erdinfitinhib treatment.
The particularly interesting aspect was that the growth acceleration occurred despite the absence of the usual endocrine explanation.
In one patient, testosterone remained extremely low and there was no evidence of pubertal progression. In the other, the patient remained Tanner stage 1 with very low estradiol and very low IGF-1. Yet growth accelerated after erdafitinib began.
In one patient, growth acceleration occurred despite stable GH dosing and without an increase in IGF-1; in the other, IGF-1 was profoundly low. The authors therefore proposed that the phenomenon represented an FGFR-related, growthfactor and sex steroid independent mechanism.
This is extremely important for the biology.
It means:
FGFR inhibition → increased skeletal growth
cannot simply be reduced to:
FGFR inhibition → higher GH/IGF-1 → growth.
There appears to be a local growth-plate mechanism.
The growth plate itself provides the explanation
FGFR3 is normally expressed in growth-plate chondrocytes and acts partly as a negative regulator of endochondral bone growth.
That means the normal growth plate isn’t operating with FGFR3 completely absent. Instead, there is a balance:
pro-growth signals
versus
anti-growth/feedback signals.
FGFR3 contributes to the latter.
So inhibiting FGFR3 can theoretically shift the equilibrium toward:
chondrocyte proliferation → hypertrophy → matrix production → ossification → longitudinal expansion.
That is why the erdafitinib observations are not biologically impossible or contradictory.
In fact, there is genetic evidence pointing in the same direction: loss-of-function FGFR3 variants in humans and animals are associated with skeletal overgrowth, and the erdafitinib authors specifically discuss the similarity between pharmacological FGFR inhibition and FGFR3 loss-of-function states
TYRA-300 makes the comparison even more interesting
Tyra-300 is another fgfr3 inhibitor, it is the most selective and expensive costing up to 1500 a month for meaningful doses
TYRA-300 provides perhaps the cleanest experimental demonstration that normal FGFR3 signaling itself can restrain growth.
Researchers deliberately administered TYRA-300 to wild-type mice from four to eight weeks of age, rather than restricting the experiment to FGFR3-mutant animals(meaning these mice were normal)
At 14 mg/kg/day, nasoanal length increased by 7.3%, while tibia and femur length also increased significantly.
That is extremely important because it establishes:
FGFR3 inhibition can increase skeletal growth even when FGFR3 is not pathologically activated.
However, the response was still generally larger in the FGFR3-driven disease models. TYRA-300 produced particularly strong effects in achondroplasia-model mice, while the hypochondroplasia model showed smaller responses because the underlying phenotype is milder.
So the emerging picture isn’t:
normal = zero response
but rather:
pathological FGFR3 activation = larger available therapeutic effect
normal FGFR3 = potentially smaller but biologically real effect.
“Erda has way better numbers so it has to be better overall”
No, and this is very important don’t skip here
The ~19 cm/year growth observation with erdafitinib is not equivalent to a 19 cm/year healthy-growth treatment effect.
The skeleton was behaving abnormally.
The patient developed:
- rapid long-bone growth
- spinal deformity
- cervical lordosis
- thoracic scoliosis
- hip-flexor contractures
- markedly elevated alkaline phosphatase
- abnormal skeletal architecture
The other report found growth-plate widening and profound metaphyseal sclerosis/mineralization changes shortly after treatment began.
There is also a published series describing slipped capital femoral epiphysis (SCFE) associated with pediatric FGFR-TKI exposure, with growth-plate widening and altered mineralization considered important contributing factors.
So erdafitinib demonstrates maximum biological disruption, not necessarily maximum desirable growth.
Why infigratinib may actually be the better “growth” experiment
Infigratinib’s effect is much less spectacular numerically, but that’s partly because its clinical program was designed around correcting pathological FGFR3 signaling rather than producing uncontrolled skeletal overgrowth.
The phase-3 result:
+1.74 cm/year vs placebo
is therefore a much cleaner measurement of a sustained therapeutic effect than a case report showing ~19 cm/year accompanied by skeletal deformity.
And its animal studies demonstrate reproducible correction of:
- long-bone shortening
- growth-plate abnormalities
- vertebral abnormalities
- skull-base abnormalities
in FGFR3-driven models.
So if the endpoint
“How much can I disrupt skeletal growth?”
erdafitinib wins the available human anecdotal evidence.
If the endpoint is:
“How convincingly can we demonstrate controlled improvement of longitudinal growth?”
infigratinib has the much stronger evidence base.
basically erda=more disruption, less safe, better numbers
Infig= bit more selective so less disruption, more clinical evidence of growth, lower numbers
“Infig inhibits fgfr3 more and is more selective than erda, why are its numbers supposedly worse?”
Erdafitinib’s broader profile may help explain why its skeletal effects can look disproportionately strong despite having weaker FGFR3 potency than infigratinib: FGFR1, FGFR2, FGFR3 and FGFR4 are not interchangeable, and all participate in skeletal development and growth-plate regulation. FGFR3 is the clearest growth-plate brake, particularly in proliferative and prehypertrophic chondrocytes, whereas FGFR1 is more prominent in prehypertrophic/hypertrophic chondrocytes and is involved in differentiation; FGFR2 has important roles earlier in chondrogenesis and osteoblast development, while FGFR4 is expressed in resting/proliferative zones and has more context-dependent functions. Thus, infigratinib’s ~1 nM FGFR3 potency does not mean it produces the largest total skeletal perturbation: it strongly inhibits FGFR1–3 but largely spares FGFR4, whereas erdafitinib inhibits all four in the low-nanomolar range (FGFR1 ~1.2, FGFR2 ~2.5, FGFR3 ~3.0, FGFR4 ~5.7 nM). A broader blockade could therefore alter several interacting regulatory compartments simultaneously, potentially producing a larger overall phenotype even with weaker FGFR3 inhibition
Conclusion, what mogs infig or erda?
it depends on what you’re looking for
| Question | Winner |
| Largest reported human growth acceleration | Erdafitinib |
| Controlled human height evidence | Infigratinib |
| Evidence specifically in achondroplasia | Infigratinib |
| Evidence in a non-dysplastic child | Erdafitinib |
| Reproducible disease-model animal evidence | Infigratinib |
| Evidence in normal/wild-type animals | TYRA-300 |
| Evidence that growth can occur independently of GH/sex steroids | Erdafitinib |
| Cleanest FGFR3-targeting concept | TYRA-300 |
| Best evidence that FGFR3 inhibition corrects pathological growth suppression | Infigratinib |
| Most dramatic but abnormal skeletal phenotype | Erdafitinib |
Infigratinib does not “mog” erdafitinib in raw growth magnitude. Erdafitinib’s accidental pediatric growth phenotype is considerably more dramatic.
But infigratinib absolutely mogs erdafitinib in evidentiary quality for controlled growth promotion: prospective trials, a defined population, a comparator group, reproducible animal data, quantified height velocity, and a coherent therapeutic rationale.
If you’re broke do erda or infig, if you have more money do hgh (8 iu minimum) paired with erda or infig. If you’re rich do high hgh and experiment with ky or Tyra.
More experimental things like sag21k, Ap-811, foxo4-dri or even epitalon on are hard to obtain and have little clinical evidence so process with caution
Sources
Sources
Sources
Sources
Sources
Sources
Sources
