An evaluation of the acidogenic potential of asthma inhalers

The aims of the present study were firstly to investigate the inherent pH and titratable acidity of commercially available paediatric asthma inhalers in the United Kingdom and secondly to assess their in vivo acidogenic potential (saliva pH and plaque pH (PpH) tests) in a group of healthy adult volunteers.

Manually actuated metered dose inhaler (MDI) and dry powder inhaler (DPI) formulations of all available preventor (glucocorticoids, disodium chromoglycate), reliever (beta(2) agonists) and combination asthma medication were investigated. The inherent pH and titratable acidity of 18 inhalers were determined and analysed using t-tests, ANOVA and post hoc Tukey's tests. Following this the oral pH responses after inhaler use were assessed in 14 healthy adult volunteers (complying with the FNDH criteria, 1985) who participated in a random blind study to determine both the salivary pH (SpH) and plaque pH following inhaler use. Non-parametric tests of significance (Mann-Whitney and Wilcoxon Signed-Ranked Tests) were used to analyse pH responses according to vehicle of delivery (MDI/DPI), lactose content and generic drug.

The inherent pH of the DPIs (n=8, mean pH=5.06) was significantly lower (P<0.005) than that of the MDIs (n=10, mean pH=6.45) and the titratable acidity of the lactose-based DPIs was twice that of the non-lactose-based DPIs (P<0.000). Lactose-based DPIs produced significantly lower salivary pH and plaque pH readings, greater maximum pH drops from baseline pH and larger areas below baseline pH in comparison with that of all other inhalers tested (P<0.05). All inhalers, however, failed to depress plaque pH below pH 6.

Although none of the inhalers were able to demonstrate an acidogenic response below the "critical" pH, the substantial pH drops observed with the lactose-based DPIs may be an important consideration for enamel demineralisation.