In 2007, researchers from Novartis Pharmaceuticals reported the results of a pre-clinical study designed to evaluate the safety of inhaled cyclosporine dissolved in propylene glycol by examining its acute effects in animals.
According to the study abstract: "The objective of these studies
was to evaluate the potential toxicity of aerosolized cyclosporine
formulated in propylene glycol when given by inhalation route to rats
and dogs for 28 days. ... Endpoints used to evaluate
potential toxicity of inhaled cyclosporine were clinical observations,
body weight, food consumption, respiratory functions, toxicokinetics,
and clinical/anatomic pathology. ... There was no unexpected
systemic toxicity or clinically limiting local respiratory toxicity
associated with inhalation exposure to cyclosporine inhalation solution
at exposures up to 2.7 times the maximum human exposure in either rats
or dogs. There were no respiratory or systemic effects of high doses of
propylene glycol relative to air controls. These preclinical studies
demonstrate the safety of aerosolized cyclosporine in propylene glycol
and support its continued clinical investigation in patients undergoing
allogeneic lung transplantation."
The Rest of the Story
This study provides pre-clinical evidence that the use of propylene glycol as an excipient for the delivery of drugs by inhalation appears to be acutely safe.
The study adds to existing evidence of the acute safety of inhaled propylene glycol. However, further study of the potential long-term effects of propylene glycol inhalation is necessary.
Nevertheless, these results help support the contention that the use of electronic cigarettes to quit smoking is a reasonable clinical approach to smoking cessation.