[Changes in specific airway resistance after powder inhalation of formoterol or salmeterol in moderate bronchial asthma].

Formoterol and salmeterol are two long acting beta 2 agonists available for the treatment of asthma which show differences in onset of action. In a multicentre parallel group study, patients with moderate asthma were investigated by measuring the specific airway resistance (sRaw), a more sensitive parameter than FEV1. A total of 99 patients were randomised for open treatment with either 12 micrograms formoterol delivered via Turbohaler or 50 micrograms salmeterol via Diskus. The patients were between 18 and 66 years of age, had a medium FEV1 of 68.8% (+/- 17.8%) predicted and showed a medium reversibility of 28.8% (+/- 16.5%). The patients response to one inhalation of the study drug was investigated by sRaw measurements 2, 5, 10, 20 and 60 minutes after inhalation of the formulation. Additionally, FEV1 was measured. The results show a significant decrease in specific airway resistance of 29% within the first two minutes in patients who had received 12 micrograms formoterol via Turbohaler. However, patients on salmeterol showed no change (sRaw +/- 1%). This difference is statistically highly significant (p < 0.0001). Furthermore, in 49% of the patients treated with salmeterol an increase in sRaw was seen immediately after inhalation of the drug. This increase was +16.4% in an average of 2 minutes after inhalation. One hour after inhalation the differences between the groups were small and not significant neither between formoterol and salmeterol-treated patients nor within the salmeterol group. In the following week patients were treated with 12 micrograms formoterol Turbohaler b.i.d. or 50 micrograms salmeterol Diskus b.i.d., respectively. A further sRaw measurement was performed 11 +/- 1 hours after the last inhalation of the drug. The results for sRaw and FEV1 show no differences between both study drugs indicating a similar duration of action for both formoterol Turbohaler and Salmeterol Diskus in moderate asthma. No serious adverse events were reported. The adverse event profile observed in both study groups was comparable. Thus, this study shows once again that formoterol delivered via Turbohaler has a more rapid onset of bronchodilating action compared with salmeterol Diskus. Furthermore the inhalation of salmeterol via Diskus in one-half of the patients led to an increase in specific airway resistance within the first minutes after inhalation. It is worth discussing whether an unspecific reaction to the relatively large lactose particles which are components of the salmeterol Diskus formulation are responsible for this observation.