The biphasic cutaneous
hypersensitivity response elicited by intradermal administration of S. haematobium
antigen to patients with
schistosomiasis may be used as a model for
drug effects on cell dynamics. As the effects of H1- and H2-blockade, and the possible involvement of H3-receptors, have not been elucidated, we have examined the effects of combinations of
cetirizine,
cimetidine and
betahistine on the response of patients with confirmed
schistosomiasis. The skin
blister technique was used. After intradermal administration of
antigen,
blister fluid containing inflammatory cells was collected on microscope slides at 6 and 24 h, and a differential cell count was done; and the area of induration was measured at 0.25, 1, 6 and 24 h. These baseline tests were repeated after 3 days of pretreatment with
cetirizine 20 mg/d, after the addition of
cimetidine 1200 mg/d for 3 further days, and finally after adding on
betahistine 32 mg/d for 3 days. Simultaneous H1- and H2-blockade with
cetirizine plus
cimetidine caused a significantly greater reduction in induration than
cetirizine (H1-blockade) alone; the reductions from the baseline value were 70%, 78%, 89%, 97%, and 33%, 53%, 43%, 30%, at times 0.25, 1, 6 and 24 h, respectively. The triple combination with the addition of
betahistine (H1- and
H2-agonist and H3-antagonist) resulted in reductions of 37%, 63%, 95% and 97% at the same times. The most striking changes in cellular dynamics were a significant increase in eosinophil (6 h) and neutrophil (6 h) vacuolation, and enhancement of monocyte (24 h) and basophil (6 h) accumulation, when the
betahistine was added.(ABSTRACT TRUNCATED AT 250 WORDS)