Bronchial hyper-reactivity in atopic patients during H2-receptor blocker treatment

Allergy-like reactions to iodinated contrast agents. A critical analysis

Allergy-like reactions may occur following administration of iodinated contrast media (CM), mostly in at-risk patients (patients with history of previous reaction, history of allergy, co-treated with interleukin-2 or beta-blockers, etc.) but remain generally unpredictable. Severe and fatal reactions are very rare events. All categories of CM may induce such reactions, although first generation (high osmolar CM) have been found to induce a higher rate of adverse events than low osmolar CM. However, no differences were found between the two categories of CM with respect to mortality. Delayed reactions can also occur. There are no differences between the various categories of CM except for non-ionic dimers, which are more likely to induce such effect. Numerous clinical studies have evaluated the prophylactic value of drugs (mostly antihistamines and corticosteroids). Results are unclear and highly variable. Any prevention depends upon the mechanism involved. However, the mechanism of CM-induced allergy-like reaction remains disputed. Relatively recent data revived the hypothesis of a type-I hypersensitivity mechanism. Positive skin tests to CM have been reported. However, the affinity of IgE towards CM has been found to be very low in the only study which actually evaluated it. Other pathophysiological mechanisms (involving direct secretory effects on mast cells or basophils, or activation of the complement system associated or not with the plasma contact system) are also much debated. Anaphylaxis and anaphylactoid reactions are, in the end, clinically undistinguishable.

Comparison of the effects of cimetidine and ranitidine in histamine provocation tests in atopic asthma

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.

The role of H2-receptors in bronchial reactivity in atopic asthma

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 influence of cimetidine and ranitidine on basophil histamine release and bronchial reactivity in asthmatic patients

Anti-IgE induced histamine release from isolated basophils after Cimetidine and Ranitidine administration was evaluated in 22 patients with atopic bronchial asthma. The histamine provocation test after Ranitidine treatment in 10 patients with atopic bronchial asthma and 10 patients with peptic ulcer was also performed. Investigations in vitro revealed that Cimetidine and Ranitidine in low concentrations had an inhibitory effect whereas in concentrations of over 10(-6) M and 10(-4) M, respectively, they enhanced histamine release. Investigations in vivo after administration of Ranitidine showed that it does not cause marked changes in the bronchial reactivity in patients with bronchial asthma and any change in patients with peptic ulcer. These preliminary studies seem to suggest that in patients with atopic bronchial asthma and concomitant peptic ulcer Ranitidine is preferable to Cimetidine in the treatment of digestive tract disorders.