Mecasermin
Increlex, rhIGF-1
Approved IGF-1, and the reference point for what supervised IGF-1 therapy involves: meal timing, glucose monitoring, and hypoglycaemia as the dose-limiting toxicity.
FDA-approved
FDA-approved as Increlex for growth failure in children with severe primary IGF-1 deficiency or with growth hormone gene deletion who have developed neutralising antibodies to growth hormone. Not approved for any use in healthy adults.
What it is
Mecasermin is recombinant human IGF-1, native sequence, manufactured as a pharmaceutical. It exists because some children cannot make IGF-1 or cannot respond to growth hormone, and in them supplying the downstream hormone directly is the only route to growth.
It appears on this site mainly as a control. It is what IGF-1 therapy looks like when a regulator has examined it.
What supervision actually involves
The label reads like a warning about the grey market version, and that is worth spelling out.
Doses are weight-based and titrated slowly against tolerance. Each injection must be given within about twenty minutes either side of a meal, because IGF-1 has insulin-like activity and dosing without food causes hypoglycaemia. Blood glucose is monitored, particularly during titration. Malignancy is a contraindication. Hearing, tonsillar size and signs of intracranial hypertension are followed.
Hypoglycaemia is not a rare idiosyncratic reaction here. It is the expected dose-limiting toxicity of the drug class, managed by protocol.
Why IGF-1 LR3 does not inherit any of this
Mecasermin is native IGF-1 with normal affinity for IGF binding proteins. Those proteins buffer its activity and localise it, and its free half-life is short.
LR3 was engineered specifically to defeat that buffering, and circulates freely for twenty to thirty hours. It is sold as a cell-culture reagent, self-administered without glucose monitoring or meal timing, at doses nobody established.
So the comparison runs the wrong way from the marketing. The approved product is the short-acting, buffered, monitored one, and the unapproved product is the long-acting, unbuffered, unmonitored one. If anything, the modifications that make LR3 attractive to buyers are the ones that remove the safeguards mecasermin's protocol is built around.
Practical notes
- The approved indication is paediatric growth failure, not adult anabolism. Nothing in this file supports use by healthy adults, and the label contraindicates it once growth plates have closed.
- It is expensive and tightly distributed. This is an orphan product, not something that leaks into general supply.
- Read the hypoglycaemia protocol as information about the whole class. Whatever is true of monitored native IGF-1 is more true of an engineered long-acting analogue taken without monitoring.
Side effects and warning signs
Commonly reported
- Hypoglycaemia, the dose-limiting toxicity and the reason for meal timing
- Injection-site lipohypertrophy
- Tonsillar and adenoid hypertrophy, which can cause snoring or sleep apnoea
- Headache
- Intracranial hypertension, uncommon
Stop and get medical help
- Any active or suspected malignancy. IGF-1 is a mitogen and this is a contraindication in the label, not a theoretical concern
- Sweating, shaking, confusion or loss of consciousness, which is hypoglycaemia and requires immediate carbohydrate
- Closed epiphyses, since the growth indication no longer applies
- Snoring or daytime sleepiness developing during treatment, which can indicate tonsillar hypertrophy