Mecasermin

In plain language

Mecasermin is recombinant human IGF-1, sold as Increlex, for children whose bodies cannot make or respond to growth hormone properly. It is injected twice a day under the skin.

IGF-1 is the messenger that carries out many of growth hormone's effects on the body's growth. Children with rare conditions like growth hormone insensitivity syndrome (Laron syndrome) cannot use growth hormone itself, so giving them the downstream messenger restores growth.

For students

Mecasermin is recombinant human insulin-like growth factor 1 (70 residues, about 7,649 Da), identical to the natural mediator of growth hormone action. GH stimulates hepatic IGF-1 production; in GH insensitivity (Laron syndrome, GH receptor mutations) or IGF-1 gene deletion, the pathway is broken downstream of GH, and exogenous GH cannot work, so IGF-1 replacement is the rational therapy.

Trials in severe primary IGF-1 deficiency showed first-year growth velocity increases (about 4 cm per year baseline rising to 8 cm per year on treatment), with sustained height gains over 2-4 years. Because IGF-1 lowers blood sugar and can enlarge lymphoid tissue, dosing is twice-daily with meals, with monitoring for hypoglycemia, tonsillar hypertrophy and intracranial hypertension (papilledema screening). It is also used in some extremely rare IGF-1 gene deletion cases and studied in diabetes complications, though the latter is not an approved use.

For researchers and instructors

Biochemistry. The GH-IGF-1 axis (hypothalamic GHRH, pituitary GH, hepatic IGF-1, chondrocyte action) is the endocrine circuit this drug completes; the lesson is pathway logic: replace the missing messenger, not the hormone that fails to work.

Pharmacology. Twice-daily subcutaneous dosing 40-120 mcg/kg with meals; half-life extended by forming ternary complexes with IGFBP-3 and acid-labile subunit (which recombinant IGF-1 alone does not, hence short effective exposure); hypoglycemia is the dose-limiting toxicity.

Human evidence. Pivotal trials in severe primary IGF-1 deficiency (n~50-100 across studies) showed growth velocity restoration; long-term extension data (up to 8 years) support continued growth without loss of effect.

Teaching point. A model of pathway replacement logic in endocrinology and of how pharmacokinetic protein-binding complexes (IGFBPs) shape dosing of a peptide drug.