PITTSBURGH — Treatment with the investigational drug capromorelin brings growth hormone levels in the elderly back into the normal range for young adults, and improves some measures of function, results from a phase II trial showed.
These results suggest the possibility that long-term treatment with the oral growth hormone secretagogue could prolong the capacity for independent living in older men and women, Dr. George Merriam and his associates reported at the International Congress of Neuroendocrinology.
“One subject said his golf swing improved … but generally it was a sense of more energy, more vim and vigor,” he said in an interview.
Growth hormone secretion declines with age, and studies have looked at the benefits of administering human growth hormone. Alternative approaches under investigation include stimulating endogenous growth hormone secretion with growth-hormone-releasing hormone (GHRH) and growth hormone secretagogues (GHSs).
Both GHRH and GHS have several potential advantages over growth hormone, he said. They stimulate pulsatile rather than continuous growth hormone release, and preserve endogenous feedback, including inhibition of growth hormone release as levels of insulinlike growth factor-I (IGF-I) rise, potentially buffering against overtreatment. Some secretagogues, including capromorelin, a mimetic of the intestinal hormone ghrelin, also have the practical advantage of being orally active, said Dr. Merriam, who has no financial interest in Pfizer Inc., which is developing the drug and sponsored the study.
He presented data from a double-blind, multicenter study in which 395 generally healthy men and women with some functional limitations were randomized to 12 months of treatment with placebo or one of four active doses of capromorelin: 10 mg three times weekly, 3 mg twice daily, 10 mg daily at bedtime, or 10 mg twice daily.
The subjects' ages ranged from 65 to 84 years, and all had a body mass index of less than 30 kg/m
Each dose of capromorelin stimulated an acute rise in growth hormone levels, reported Dr. Merriam, of the University of Washington in Seattle. Capromorelin stimulated a dose-related increase in circulating IGF-I levels, with the greatest increases at the highest dose. These increases were sustained for the duration of treatment, but returned to baseline after the drug was discontinued.
Patients on active treatment gained a mean of 1.6 kg more than those on placebo after 6 months, and 1.3 kg after 12 months. This reflected an increase of 1.4 kg in lean body mass after 6 months and 1.6 kg after 12 months.
Tandem walk times improved significantly at 6 months and even more so at 12 months, compared with placebo. Stair climbing power improved significantly at 12 months.
Nonsignificant trends toward improvement were seen in the 6-minute walk, chair rises, and tandem stand tests.
The drug was generally well tolerated. Insomnia and statistically significant increases in fasting glucose levels were reported in the active treatment groups. But glucose levels remained within the normal range, Dr. Merriam said.
The physical function results are similar to those recently reported for Merck's investigational growth hormone secretagogue, MK677, which has a similar structure to capromorelin, he said. But both drugs face an uphill regulatory battle because the Food and Drug administration does not consider aging to be a disease.
“These are very encouraging data, but they're not the sort of thing that can be sent in to the FDA and get an approval from,” Dr. Merriam said. “It's too small, too limited a study, but it's very intriguing.”