The relationship of inhaled sulfur dioxide reactivity to ingested metabisulfite sensitivity in patients with asthma.

When ingested in acid solution, the preservative sodium metabisulfite (MB) provokes asthma within minutes of ingestion in a proportion of asthmatic subjects. Freshly prepared acid solutions of MB liberate significant quantities of gaseous SO2. In order to test the hypothesis that asthma provoked by ingestion of acidified solutions of MB was due to supersensitivity to SO2 inhaled during swallowing, 3 groups of 10 subjects were studied. Groups 1 and 2 were asthmatics. Group 1 subjects were reactors and Group 2 were nonreactors to ingested MB. Group 3 subjects were nonasthmatic control subjects. Subjects were challenged, on separate days, with 50 mg of MB in citric acid and SO2 gas, via a steady-state system, at increasing concentrations (0.5, 1.5, 3, 5 ppm). The mean percent fall in peak expiratory flow rates after ingestion of MB for Group 1 was 35 +/- 14, Group 2 was 6 +/- 6, and Group 3 was 5 +/- 3. The mean SO2 provocation concentration (Pc20.SO2) for Group 1 was 1.19 +/- 0.78 ppm, for Group 2 it was 2.25 +/- 1.42 ppm, and for Group 3 it was greater than 5 ppm. The means for Pc20.SO2 of Groups 1 and 2 were not statistically different (p = 0.075), although the possibility of a Type 2 error is recognized. Five MB-sensitive subjects were subsequently challenged with the MB solution by mouthwash and nasogastric tube. Asthma was provoked in all 5 subjects by mouthwash but not by gastric challenge.(ABSTRACT TRUNCATED AT 250 WORDS)