a Review on the Safety of Inhalation of Propylene Glycol in E-cigarettes

Introduction:
This article reviews the safety of inhalation of propylene glycol (PG), a major component of e-cigarettes, by summarizing available animal and human studies. The review highlights the inhalation safety of PG and its metabolism, pharmacokinetics, and elimination.

Key Points:

* PG is metabolized into pyruvic acid, acetic acid, lactic acid, and propionaldehyde.
* PG has a relatively short plasma half-life (4-8 hours) and is mainly excreted in the urine as the glucuronide conjugate, but 12-45% is excreted unchanged.
* The inhaled dose of PG from normal e-cigarette use is 0.3 to 0.45g/day, and serious toxicity generally occurs at plasma concentrations over 1g/L.
* animal studies have shown that PG does not appear to pose a significant hazard via the inhalation route, even at concentrations higher than those used in e-cigarettes.
* Suber et al. (1989) exposed rats to PG aerosol and found no significant differences in respiratory rates, minute volumes, or tidal volumes. however, female rats exposed to high concentrations of PG showed a decrease in feed consumption.
* Montharu et al. (2010) subjected rats to 25mg/kg/day of PG for 4 days and found limited cellular reaction and no respiratory or systemic effects. however, respiratory arrests occurred on the third day of administration.
* Werley et al. (2011) exposed rats and dogs to high concentrations of PG aerosol and found no remarkable in-life findings or histopathological effects on the respiratory system.
* heck et al. (2002) demonstrated that the addition of PG to cigarettes has no meaningful effect on the site, occurrence, or severity of respiratory-tract changes or on the measured indices of pulmonary function.
* Gaworski et al. (2010) observed that the addition of PG to experimental cigarette tobacco reduced the presence and severity of some histopathological lesions.

Main Message:
The review highlights the inhalation safety of PG, as shown in various animal studies. The concentrations of PG used in e-cigarettes appear not to have any toxic effects, but further human studies need to be conducted to confirm the safety of inhalation of PG from e-cigarettes. The main message is that PG is relatively safe for inhalation, and the concentrations used in e-cigarettes are within the safe range. however, more human studies are needed to confirm these findings.

Cotta, Karyn. “a Review on the Safety of Inhalation of Propylene Glycol in E-Cigarettes.” Global Journal of Pharmacy & Pharmaceutical Sciences 2, no. 2 (May 30, 2017). https://doi.org/10.19080/GJPPS.2017.02.555584.