Mecasermin

Mecasermin is unmodified human IGF-1 produced in E. coli. In severe primary IGF-1 deficiency the GH receptor or its downstream signalling is broken, so giving more GH does nothing and the missing hormone must be replaced directly. Because it is the native sequence, it binds IGFBP-3 normally, which is both why it needs twice-daily dosing and why circulating levels depend on the patient's acid-labile subunit and IGFBP-3 status. Receptor activation drives PI3K/Akt/mTOR-mediated growth in the epiphyseal growth plate, muscle and other tissues, and appreciable cross-reactivity with the insulin receptor produces the hypoglycaemia that dominates its safety profile.

Targets: IGF-1 receptor (IGF1R), Insulin receptor (cross-reactivity), IGFBP-3 / ALS ternary complex

• · The label starts at 0.04-0.08 mg/kg twice daily and titrates by 0.04 mg/kg increments to a maximum of 0.12 mg/kg twice daily. The microgram figures here are per kilogram, not absolute.
• · No approved adult indication and no validated adult dosing. Off-label use for performance carries the label's hypoglycaemia risk without any of its evidence.

Work out your exact syringe units →

• very commonHypoglycaemia— The dominant adverse effect. Meals must be taken with every dose; severe episodes with seizure or loss of consciousness have occurred.
• commonInjection-site lipohypertrophy or reaction— Rotate sites.
• commonTonsillar and adenoid hypertrophy— Can cause snoring and sleep apnoea; the label calls for periodic assessment.
• uncommonIntracranial hypertension (papilloedema, headache, vomiting)— Usually reversible on interruption or dose reduction; fundoscopy is recommended if symptoms appear.
• uncommonSlipped capital femoral epiphysis and scoliosis progression— A hazard of rapid growth in children.
• rareHypersensitivity and anaphylaxis— Reported post-marketing.

• Active or suspected neoplasia - stop immediately if malignancy develops.
• Closed epiphyses when used for growth promotion.
• Known hypersensitivity to mecasermin or benzyl alcohol (the vial preservative).
• Do not use in neonates because of the benzyl alcohol content.

• cautioninsulin-analogues — Insulin doses often need reducing; the hypoglycaemia is additive and clinically significant.
• cautionsomatropin — Not the standard approach - mecasermin exists precisely for patients in whom GH does not work.

• · Blood glucose before and after dosing, especially during titration.
• · Fundoscopic examination at baseline and if headache, nausea or visual change appears.
• · Tonsil and adenoid assessment, and screening for sleep apnoea.
• · Hip and spine examination in growing children.
• · Serum IGF-1 to guide dose.

Prescription drug approved in the US and EU for a narrow paediatric indication. Prohibited in sport at all times by WADA.

• Increlex (mecasermin) FDA prescribing information (label)
• Long-term growth-velocity studies of rhIGF-1 in severe primary IGF-1 deficiency (trial)

Mecasermin matters to this class not because anyone uses it for physique but because it is the only IGF-1 in existence with real pharmacokinetics, a real adverse-event denominator and a regulator's read of the file. Everything the grey market claims about LR3 and DES can be sanity-checked against it. The pharmacology that the label makes visible is the binding-protein dependency: clearance varies fourfold with IGFBP-3 status, so the same milligram-per-kilogram dose produces radically different exposure in a person with low versus normal IGFBP-3. That is the same physiology the engineered analogues deliberately break, and it is why 'evading binding proteins' is a potency change, not a duration change. Receptor biology is textbook IGF1R: autophosphorylation, IRS-1 and Shc docking, PI3K-Akt driving mTORC1 translation initiation and FoxO nuclear export, MAPK driving proliferation, and enough insulin-receptor and hybrid-receptor engagement to move blood glucose hard. The label's numbers put a floor under how seriously to take that last part - 42% of 71 trial subjects had at least one hypoglycaemic episode, five had severe hypoglycaemia requiring assistance and four had seizures or loss of consciousness. That is with weight-based dosing, prescribed food timing, and clinical supervision. The soft-tissue growth signal is equally instructive: tonsillar hypertrophy in 15% of subjects within the first one to two years, seven of whom needed surgery. IGF-1 receptor agonism grows lymphoid tissue as readily as it grows muscle, and nothing about a grey-market analogue changes that.

The clinical failure mode is hypoglycaemia in a child who did not eat, which is why the label ties every injection to a meal and says to skip the dose if the meal is skipped rather than dose and hope. The second is escalating too fast: the required week of tolerance at each step exists because the hypoglycaemia rate is highest in the first month and in younger patients. The third is missing the slow soft-tissue signals - tonsillar hypertrophy presenting as snoring, intracranial hypertension presenting as headache - because both develop over months and neither announces itself.

1. —Week 1 onward — 0.04 to 0.08 mg/kg twice daily subcutaneously. Weight-based, so there is no fixed microgram figure. Each injection goes within 20 minutes either side of a meal or snack.
2. —After at least one week without hypoglycaemia or other issues — Increase by 0.04 mg/kg per dose. The label is explicit that you do not escalate until the previous step has been tolerated for a week.
3. —Maintenance — Maximum 0.12 mg/kg twice daily. Do not increase further to chase growth velocity.

• IGF-1 receptor (IGF1R) — Native ligand affinity, low nanomolar

  Full agonism; the entire therapeutic effect in growth failure, and the source of the mitogenic and soft-tissue growth concerns.

• IGFBP-3 and the acid-labile subunit ternary complex — High; over 80% of circulating IGF-1 is complexed to IGFBP-3 plus ALS

  Not a signalling target. It is the reservoir that determines clearance, and in severe primary IGF-1 deficiency it is depleted, which is why these patients clear the drug faster.

• Insulin receptor — Roughly 100-fold weaker than insulin

  Glucose lowering. At therapeutic doses this is clinically significant, not trivial.

Glucose effects are immediate and dose-limiting from the first injection. Height velocity changes take months and are assessed over years. Tonsillar hypertrophy and organ growth are first-one-to-two-year phenomena.

Mecasermin is not a stacking compound and the label treats concomitant insulin or oral hypoglycaemics as a dose-reduction trigger rather than a synergy. The interaction worth naming for this audience is with growth hormone: in patients with GH insensitivity the two are alternatives, not partners, and combining them raises exposure on both sides of the axis without a clinical rationale. The one genuinely useful cross-reference is that IGFBP-3 status determines clearance, so anything that raises IGFBP-3 - growth hormone in particular - will slow mecasermin clearance and raise exposure at a fixed dose.

Mecasermin is the control condition for this whole corner of the class. It is the same receptor pharmacology as LR3 and DES with none of the engineering, and it comes with the numbers those two do not have: measured bioavailability, measured volume of distribution, measured half-life, measured clearance and a documented 42% hypoglycaemia rate under supervision. When someone tells you LR3 at 50 mcg is a low dose, the useful reply is that a 30 kg child on 0.08 mg/kg twice daily is getting 4.8 mg a day of the unmodified molecule under a physician with a glucose meter, and 42% of that cohort still went hypoglycaemic. The engineered analogues are more potent per microgram than the reference drug, not less.

Increlex is a specialty biologic dispensed through limited-distribution pharmacies and priced per milligram at levels that put a month of weight-based dosing in the thousands of dollars. No verified current price was resolved, so no figure is given rather than a guess.

• ?Tmax after subcutaneous administration is not stated in the label sections retrieved, so it is left null rather than estimated.
• ?The 0.257 L/kg volume of distribution is from patients with severe primary IGF-1 deficiency, who have abnormally low IGFBP-3. In a person with normal binding proteins the distribution volume would be smaller and the half-life longer.
• ?Protein binding is entered as 80% because the label describes over 80% of circulating IGF-1 as complexed with IGFBP-3 and the acid-labile subunit. This is a physiological statement about IGF-1 generally, not a formal plasma-protein-binding measurement of the drug.
• ?Blood-brain barrier penetration is marked partial on the basis of general IGF-1 transport physiology, not a mecasermin-specific study.
• ?No verified current acquisition cost was found.

• INCRELEX (mecasermin) injection, solution - FDA prescribing information Ipsen Biopharmaceuticals, Inc., DailyMed, U.S. National Library of Medicine

  Source of every pharmacokinetic and adverse-event number in this record: near-100% subcutaneous bioavailability, 0.257 L/kg volume of distribution, 5.8 hour terminal half-life, IGFBP-3-dependent clearance of 0.01-0.04 L/hr/kg, 42% hypoglycaemia and 15% tonsillar hypertrophy.