Walvoord, E. C. et al. Inhaled growth hormone (GH) compared to subcutaneous GH in children with GH deficiency: pharmacokinetics, pharmacodynamics and safety. J. Clin. Endocriol. Metab. 94, 2052–2059 (2009).

Delivery of growth hormone to children by inhalation is a viable alternative to daily injection, according to the results of a proof-of-principle study funded by Indiana-based pharmaceutical company, Eli Lilly.

Growth-hormone replacement therapy has been available since the late 1950s; however, despite huge advances in the development of drug-delivery systems, daily injection remains the only route of administration. A major problem associated with the use of daily injection—at least in children—is that of poor adherence, which in turn results in reduced treatment efficacy. The time seems ripe, then, for an alternative approach: one possibility is an inhaled formulation of growth hormone.

Inhaled growth hormone has already undergone preliminary efficacy and safety testing in adults. Emily Walvoord (Indiana University School of Medicine, Indianapolis) and co-workers now present the results of a multicenter, randomized, placebo-controlled, crossover study of inhaled versus subcutaneous growth hormone in 22 children with growth-hormone deficiency.

The children enrolled in the study received inhaled growth hormone plus subcutaneous placebo or subcutaneous growth hormone plus inhaled placebo for 7 days. After a short washout period, all of the children commenced a 7-day crossover treatment phase.

The researchers found that inhaled growth hormone was absorbed faster than subcutaneous growth hormone: the maximal growth hormone concentration was observed 1–4 h after inhalation, versus 2–8 h after injection. The mean relative bioavailability of inhaled growth hormone was 3.5%, a value around half of that previously reported in adults. The mean relative biopotency of the inhaled formulation was 5.5%. Inhaled growth hormone was well tolerated and no changes in pulmonary function were recorded. The inhaled route of delivery was preferred by both patients and their parents or guardians, and use of the inhaler deemed easy to learn.

Walvoord and colleagues' results suggest that inhaled growth hormone might provide an attractive alternative to the traditional route of delivery, especially for children with a fear of needles. The issue of low bioavailability remains a worry, however, and additional studies will be required before the promise of inhaled growth hormone becomes a reality.