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The objective was to investigate whether acute metabolic acidosis could cause bronchodilation in patients with asthma. Twelve patients with asthma (8 females, mean age 39 (+/- SD 12) years, forced expiratory volume in 1 second [FEV(1)] 93 [+/-9] % predicted, PC(20) 1.9 (+/-1.0) mg/mL) participated in a double-blind, placebo-controlled trial. Subjects ingested calculated amounts of ammonium chloride to induce acidosis or saline as placebo, in random order, each on a separate day. Airway resistance (R(aw)), specific airway conductance (sG(aw)), FEV(1), and PEF were measured as primary variables. To evaluate the consequences of alterations in bronchial contractility on the airway responsiveness, the histamine provocation test (PC(20)) was measured as secondary variable. The intervention resulted in a mean (SD) decrease in base excess from -0.5 (+/-1.4) to -3.9 (+/-1.1) mmol/L (p < 0.01) and a decrease in pH from 7.41 (+/-0.02) to 7.36 (+/-0.02) (p < 0.01). This caused a statistically significant increase in sG(aw) from 1.15 (+/-0.16) to 1.26 (+/-0.13) 1/kPa.s) (p < 0.05). Tendencies towards increase were found in PEF (7.79 (+/-2.2) versus 8.09 (+/-1.9) (NS, p = 0.10) and in FEV(1) (2.98 (+/-0.9) versus 3.06 (+/-0.9) (NS, p = 0.15). PC(20) did not change significantly. It was concluded that acute metabolic acidosis has a modest bronchodilating effect in patients with asthma.

Regular use of beta2-agonists might result in increased bronchial hyper-responsiveness (BHR) and decreased forced expiratory volume in 1 sec (FEV1). It has been suggested that these possible detrimental effects are not a real deterioration of the disease, but that it might be only a transient (rebound) effect shortly after discontinuing this regular use. Moreover, these effects are thought to occur especially during short-acting and not during long-acting beta2-agonists use. The aim of this study was to invest gate whether a rebound effect (a pharmacological deterioration effect diminishing after several hours) in FEV1 and PC20 (concentration of histamine causing a 20% fall in FEV1 with regard to baseline) occurred after cessation of regular use of beta2-agonists, and whether this occurred both after short-acting and long-acting beta2-agonists. Allergic asthmatic patients (n = 134) were randomly allocated to the use of a short-acting (salbutamol), a long-acting beta2-agonist (formoterol) or placebo for 12 weeks (double-blind, double-dummy). No other asthma medication was allowed, including inhaled corticosteroids. At the start and every 4 weeks later FEV and PC20 were measured, each time at least 12 h after the last doses of study medication, which is in the possible rebound period. To investigate whether a (transient) rebound effect occurred, parameters were additionally measured at least 72 h later after discontinuation of the study medication. After 12 weeks of short-acting beta2-agonist use, a drop was seen in FEV1 from 85.6 (+/- 2.21)% predicted to 78.8 (+/- 2.9)% predicted, measured 15 h (median) after the last doses of medication. This was significantly different compared to placebo. When measured 168 h (median) later FEV1 recovered to 85.5 (+/- 2.4)% predicted, comparable to baseline. PC20 decreased with -1.17 (+/- 0.44) doubling dose after 12 weeks of short-acting beta2-agonist use, measured 15 h after the last doses of medication, which was significantly different compared to placebo. However, 168 h later PC20 recovered slightly with +0.55 (+/- 0.34) doubling dose, but this value was still lower compared to placebo. In contrast, during long-acting beta2-agonist and placebo use no significant changes were seen. In conclusion, the use of short-acting beta2-agonists resulted in a transient (rebound) effect in FEV while the effects on PC20 may point to a real deterioration of the disease. Long-acting beta2-agonist and placebo use showed no changes. We conclude that a mono-therapy of short-acting and not of long-acting beta2-agonists might have deleterious effects in asthma.