Dispersing the Mists: An Experimental History of Medicine Study into the Quality of Volatile Inhalations

Dr. Nelson's Improved Inhaler was first marketed with an advertisement in The Lancet in 1865. Revolutionary at the time for its ease of use and patient-friendliness, the inhaler is still in use for self-treatment by many all over the world. On the occasion of its 150th anniversary, this study reports an experimental historical medicine approach to identify evidence for the quality of vapor inhalers.

Through accessing reviews of the device's use by the contemporary medical establishment, it was established that Dr. Nelson's Inhaler enjoyed a reputation of quality and efficacy among reputable physicians generating empirical evidence of clinical performance. There was a general absence of product performance tests during this period. Therefore, modern inhalation performance testing was applied to test the aerosol delivery performance for Friars' Balsam, and its key chemical constituent, benzoic acid (BA).

A respirable dose of 59.9 ± 9.0 μg of BA was aerosolized in a 10 minutes period from a dose of 3.3 mL Friars' Balsam (equivalent to 35.1 ± 0.2 mg of BA) in 375 mL of steaming water using the glass twin stage impinger at a flow rate of 60 L·min^-1. The respirable dose from a standardized aqueous BA inhalation formulation increased from 115.9 ± 10.6 to 200.2 ± 19.9 μg by increasing the simulated inhalation period from 5 to 10 minutes. When tested with a simulated inhalation maneuver (500 mL tidal volume, 13 minutes^-1 respiration rate, 1:2 inspiratory:expiratory ratio) a respirable dose of 112.8 ± 40.3 μg was produced.

This work has highlighted the potential for aerosol drug delivery using steam inhalers that are popular with patients. Physicians should therefore be aware of the potential for lung dosing with irritants when patients self-medicate using the Nelson Inhaler with vaporizing formulations such as Friars' Balsam.