The effects of combined H1 and H2 histamine antagonists on alterations in nasal airflow resistance induced by topical histamine provocation.

A clinical trial was undertaken to assess the effects of oral H1 (diphenhydramine hydrochloride) and H2 (cimetidine) histamine blockade on nasal resistance induced by topical histamine. Ten adult volunteers were tested on two separate occasions. Their noses were pretreated by oral administration of either combined H1 and H2 histamine antagonists or H1 antagonist and placebo. The nasal airflow resistive response to topical histamine was then determined. Combined histamine antagonism was significantly more effective in reducing the nasal resistive response to topical histamine than H1 antagonist alone (p less than 0.0001). Furthermore, ingestion of the oral H1 histamine antagonist, diphenhydramine hydrochloride, alone led to an increase in resistance of the unprovoked nose, whereas combined H1 and H2 antagonism did not lead to a significant change.