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Inhaled medication administered via a metered dose inhaler (MDI) is often used to treat asthma. Hydrofluoroalkane (HFA) has replaced chlorofluorocarbons (CFC) as the propellant and these new MDI may contain alcohol. This raises concerns that their use may transiently increase breath ethanol concentration (BEC), thereby interfering with random breath testing. It was hypothesized that HFA–ethanol MDI may contribute to raising BEC above the legal limit.The effect of a HFA–ethanol MDI on BEC was compared with that of CFC and placebo MDI and the effect of ingesting a standard amount of alcohol was also investigated. Asthmatic (n = 16) and normal control subjects (n = 15) were recruited for the double-blind, placebo-controlled study. Each subject used the three MDI in random sequence. BEC was measured at baseline and at 2, 5 and 15 min after inhalation of each MDI, using the Lion Alcometer SD-400TM. Spirometry was performed at baseline and 20 min after the last inhalation. An identical procedure was followed after alcohol consumption.Use of the HFA–ethanol MDI resulted in a significant increase in BEC from 0.002 to 0.0138 mg/100 mL (28 mg/100 mL of blood, P = 0.001) in asthmatics, and from 0.001 mg/100 mL to 0.016 mg/100 mL (33 mg/100 mL of blood, P = 0.002) in normal subjects. By 5 min, there were no significant differences in BEC of asthmatics (0.0031 mg/100 mL) and normal subjects (0.003 mg/100 mL), when compared with baseline (P > 0.2).BEC are transiently elevated after inhalation of HFA–ethanol MDI; however, by 5 min, BEC had already returned to baseline levels. Thus the effect of HFA–ethanol MDI on BEC is transient and would be negligible after 5 min.