The aim of the present study was to evaluate lung function and bronchial reactivity during therapy with the H2-blockers, cimetidine and ranitidine, in order to determine the role of H2-receptors in the bronchial response of asthmatic patients. Bronchial reactivity was evaluated by the histamine provocation test before, and 3 or 6 days after administration of cimetidine (800 mg per day) or ranitidine (300 mg per day). It was shown that after 6 days treatment, an increase in bronchial reactivity occurred in 85% of the patients treated with cimetidine and in 64% of the patients treated with ranitidine. These results seem to confirm the presence of H2 receptors in the bronchial tree of asthmatic patients. Blockade of these receptors causes an increase in bronchial reactivity and potential exacerbation of the asthmatic symptoms.

The effects of cimetidine and ranitidine on the bronchial reactivity in the group of 10 patients with atopic bronchial asthma are presented. The patients received 800 mg of cimetidine daily for 6 days and, after a three-day interval, 300 mg of ranitidine daily for a further 6 days. Bronchial reactivity to histamine was determined before the administration of each drug and on the third and sixth days of each course of treatment. A comparison of the effect of cimetidine and ranitidine on the bronchial reactivity of the same patients revealed that after 3 days' exposure to each of the two drugs, cimetidine enhanced bronchial reactivity to a statistically (p less than 0.05) greater extent than ranitidine. Bronchial reactivity was found to increase significantly after 6 days of treatment with each of the drugs but no statistically significant differences were noted on comparing the effect of these drugs. The results seem to indicate that H2 receptor antagonists may cause bronchoconstriction in some patients with bronchial asthma. The blocking effect depends on the type of the drug used and is connected with the chemical structure of the compounds.

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