The effect of topical sodium cromoglycate on intranasal histamine challenge in allergic rhinitis.

Topical sodium cromoglycate is used to treat allergic diseases of the upper and lower airways. To investigate its mechanisms of action, intranasal histamine challenge was used in nine subjects with perennial allergic rhinitis. After a preliminary day where subjects' reactivity thresholds (D100) for histamine were determined, intranasal sodium cromoglycate was administered in a double-blind, placebo-controlled fashion. Graded (D100/3, D100, D100X3), sequential challenges were performed on days 1 and 21 of each course, and responses measured by changes in nasal airway resistance, sneezes, secretion volume and secretion content: total protein, lysozyme and mucin. After a single dose of sodium cromoglycate, there was no change in resistance, but secretion volumes fell significantly (3.12 ml/5 min c.i. 2.83-3.4; placebo 3.61, c.i. 3.32-3.90: P = 0.026). After a 3-week-course, there was a significant fall in resistance (4.29 cm H2O/l/s, c.i. 3.85-4.72; placebo 5.45, c.i. 5.01-5.88: P < 0.0001). No change in other parameters was observed. Thus, in perennial allergic rhinitis, intranasal sodium cromoglycate has both short- and long-term effects on nasal reactivity to histamine challenge. Acutely, there is a reduction in nasal lavage fluid volume which may be the result of reduced irritant receptor activity. After a 3-week course, there is a reduction in nasal resistance responses, a possible anti-inflammatory effect.