Growth hormone (GH) replacement therapy is one of the few effective treatments available today to help children with PWS overcome some of the problems associated with the disorder. Kids with PWS are generally troopers when it comes to receiving their daily GH shot, but, wouldn't it be nice if they could get the same result without the needle?
To try to address this issue, drug companies have been exploring the possibility of delivering GH via inhalation - similar to the way asthma drugs can be delivered. Prior to the study described below, the Eli Lilly pharmaceutical company had begun testing an inhaled formulation of growth hormone (termed somatropin inhalation powder, SIP). They had previously shown that the SIP method safely and effectively delivered GH in a 6-month study of healthy adults, and also was safe in a one-month study of adults with mild to moderate asthma. Notably, however, it took considerably more GH delivered through inhalation to reach the same levels in the blood as when it was delivered by injection - a significant issue given the high cost of GH.
In a study just out in the Journal of Clinical Endocrinology and Metabolism [Inhaled Growth Hormone (GH) Compared with Subcutaneous GH in Children with GH Deficiency: Pharmacokinetics, Pharmodynamics, and Safety], the ability of SIP to safely and effectively deliver GH in children is examined. The authors tested in SIP in twenty-two children with GH deficiency (none diagnosed with PWS), for a period of 7 days, and compared it with the typical subcutaneous (under the skin) injection. First the good news: GH delivered by SIP appeared safe and was able to get into the bloodstream at therapeutic levels. Not surprisingly, kids preferred inhaled GH to the shot. The bad news? Unfortunately, the dose of GH needed to reach levels consistent with that achieved by needle injection was very high. The authors expected this to some extent - in adults, it takes about 10x more GH via inhalation to achieve the same blood levels as injection. However, in kids, this 'bioavailability' was even worse -- on average, only 3.5% of the delivered dose made it into the bloodstream. Kids would have to get about 15-20-times more GH each day by inhalation to achieve comparable blood levels as injected GH. Why the bioavailability in kids was even worse than adults is not entirely clear, but may well have to do with differences in anatomy of the airway between children and adults (proving once again that children are not just small adults).
Given that GH already costs tens of thousands per year, and that this inhaled GH would require more than 10x as much drug to achieve the same result, SIP does not seem like a very feasible way to go. Apparently Lilly came to the same conclusion - the paper states that the findings of the study have 'delayed ongoing development of SIP', signaling that the company will likely abandon this approach to GH therapy. So, at least for now, our kids will need to put up with their nightly needle...