A modified version of growth‑hormone‑releasing hormone (PEG‑GHRH) stays in the body longer, causing a clear rise in growth hormone for up to 12 hours after one shot and even longer with repeated doses, especially in older people. It also raises IGF‑1 levels. Side effects are mild injection‑site irritation, but repeated dosing in older adults can slightly worsen glucose tolerance. No immune reactions were seen.

The clinical use of growth hormone-releasing hormone (GHRH) is limited by its short half-life. Polyethylene glycol-conjugated GHRH (PEG-GHRH) was developed to provide increased stability compared with the currently available GHRH(1-29). This study aimed to evaluate the safety, tolerability and pharmacodynamics of PEG-GHRH. PEG-GHRH was administered by subcutaneous injection to young healthy men (n = 12) and elderly men and women (aged > 60 years; n = 20). In both groups, administration of PEG-GHRH generated a clear increase in circulating GH compared with placebo. Following single-dose (0.25, 0.5, 2 or 4 mg) administration to young subjects, the effect persisted for 12 h, but a sustained increase was observed on repeated administration to the elderly. Serum insulin-like growth factor-I also increased in response to PEG-GHRH treatment. Injection-site reactions were more frequent with PEG-GHRH compared with placebo, but these were mild and transient; other adverse events were similar to those observed after placebo. Some impairment of glucose tolerance was observed in the elderly following repeated administration of PEG-GHRH. Antibodies to GHRH were not observed. PEG-GHRH offers the possibility of less frequent dosing compared with GHRH. This possibility deserves further clinical testing.