Mecasermin rinfabate
IGF-1 pre-bound to its binding protein, approved in 2005 as iPlex and no longer marketed in the US
Mecasermin rinfabate is recombinant IGF-1 delivered already attached to IGFBP-3, the protein that carries it in blood. Binding it was meant to lengthen its action and reduce low blood sugar. FDA approved it as iPlex for severe IGF-1 deficiency; Drugs@FDA now lists that product as discontinued.
What is it?
IGF-1 drives growth in childhood, and children whose bodies cannot make it grow poorly. Most IGF-1 in blood travels bound to IGFBP-3, which extends its life and buffers its sugar-lowering effect. Mecasermin rinfabate gives the two together, in equal amounts, so a daily injection behaves more like the body's own circulating complex than free IGF-1 does.
FDA approved it as iPlex for severe primary IGF deficiency and for patients with growth hormone gene deletion who develop neutralising antibodies to growth hormone. In those conditions it increased growth velocity, and a 2008 review found its effects across diabetes, insulin resistance, burns and growth disorders largely similar to free IGF-1.
The product is no longer sold in the US: Drugs@FDA lists iPlex as discontinued. Free IGF-1, mecasermin, remains the approved option for the growth indication.
Its later work moved to newborns. In a phase 2 trial in extremely preterm infants, continuous intravenous infusion raised serum IGF-1 toward intrauterine levels, with 66.3% of measurements in range against 17.3% in controls and no adverse events attributed to the drug. The aim was to prevent retinopathy of prematurity.
At a Glance
Every value in this table is printed from the Grey Peptides dataset, the same record the compound explorer and comparison tool read, so the three can never disagree.
Educational information, not medical advice. The doses on this page come from approved labels, published studies and, where no study exists, amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
Half-Life: How Much Remains
The dataset records a half-life of about 21 hours for IGF-I after the complex (four adults) for Mecasermin rinfabate. After each half-life, half of what was in the circulation is gone, so about 3% remains after five. Real clearance varies with the person, the dose, the route and kidney or liver function; this is arithmetic on a published figure, not a dosing tool.
Published Research
These are the studies that describe mecasermin rinfabate, read from their PubMed abstracts: a phase 2 trial in preterm infants and two reviews.
Extremely preterm infants
In a phase 2 trial in infants born before 28 weeks, nine received continuous infusion averaging 95.1 µg/kg/day for 14.2 days and ten standard care. 66.3% of IGF-1 readings were in target against 17.3%, with no drug-related adverse events and no rise in infections.
The approval
Approved by FDA for severe primary IGF deficiency and for growth hormone gene deletion with neutralising antibodies, where it increased growth velocity. Binding IGFBP-3 addresses free IGF-1's short half-life and hypoglycaemia in these patients.
Across conditions
A review of its pharmacokinetics, safety and efficacy across diabetes, severe insulin resistance, osteopaenia, burns and growth hormone insensitivity, finding outcomes similar to free IGF-1 in each.
Side Effects & Contraindications
Reported Side Effects
From the reviews and the preterm trial.
Contraindications & Cautions
No longer marketed in the US.
Legal Status
Mecasermin rinfabate was approved in the US and is no longer marketed there.
Frequently Asked Questions
?What is mecasermin rinfabate?
Recombinant IGF-1 delivered already bound to IGFBP-3, its natural carrier protein, sold as iPlex.
?What was it approved for?
Severe primary IGF deficiency, and growth hormone gene deletion with antibodies to growth hormone.
?Can I get it now?
Not in the US. Drugs@FDA lists iPlex as discontinued; free IGF-1, mecasermin, remains approved.
?Why preterm babies?
Very premature infants have low IGF-1, which is linked to retinopathy of prematurity. A phase 2 trial tested restoring it by infusion.
References
- [pubmed] Hansen-Pupp I, et al. "Continuous longitudinal infusion of rhIGF-1/rhIGFBP-3 in extremely preterm infants: Evaluation of feasibility in a phase II study." Growth Horm IGF Res, 2017;36:44-51. PMID: 28934640.
- [pubmed] Kemp SF. "Mecasermin rinfabate." Drugs Today (Barc), 2007;43(3):149-55. PMID: 17380212.
- [pubmed] Williams RM, et al. "Mecasermin rinfabate: rhIGF-I/rhIGFBP-3 complex: iPLEX." Expert Opin Drug Metab Toxicol, 2008;4(3):311-24. PMID: 18363546.
- [pubmed] Camacho-Hübner C, et al. "Pharmacokinetic studies of recombinant human insulin-like growth factor I (rhIGF-I)/rhIGF-binding protein-3 complex administered to patients with growth hormone insensitivity syndrome." J Clin Endocrinol Metab, 2006;91(4):1246-53. PMID: 16403822.
- [other] US FDA, Drugs@FDA (openFDA): IPLEX (mecasermin rinfabate), Insmed, BLA 021884, Discontinued. Read September 30, 2026.
Sources & Citations
Every study here was read from its PubMed record. US status comes from openFDA, read September 30, 2026.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Consult a licensed healthcare provider before making health decisions.