Longitudinal infusion of a complex of insulin like growth factor I and IGF binding protein 3 in five preterm infants: pharmacokinetics and short term safety Pediatric Research Same molecule. Longer leash. IGF 1 LR3 is a long arginine 3 analog of insulin like growth factor 1. The Arg3 substitution prevents binding to IGFBP 3, the carrier protein that normally clears IGF 1 from circulation. Half life IGF 1 LR3 Kallista Labs IGF LR3 Natural Med Doc IGF 1 LR3 1mg Peptide: Growth Factor Research