The objectives of this study were two-fold: to identify tear
histamine content and its relationship to changes in tear
histaminase activity during the early (EPR) and late phases (LPR) of the
allergic reaction induced by a conjunctival provocation test (
CPT) and to evaluate the effects of
lodoxamide on histamine release and allergic signs and symptoms during EPR and LPR. A baseline
CPT was administered to 20 allergic patients with no baseline signs or symptoms of
allergy. Clinical signs and symptoms were evaluated after 20 minutes and 6 hours. Tear samples were taken after 5-10 minutes and after 6 hours for subsequent analyses of cytology and
histamine content (ELISA). Patients were then randomly assigned to receive
lodoxamide or placebo four times daily for one week in a double-masked fashion. A second
CPT was done after this
therapy and the same parameters were re-evaluated. During EPR, tear
histamine increased significantly with respect to baseline values (p < 0.05). During LPR, tear
histamine increased significantly (p < 0.05) only in
histamine inactivated samples.
Histaminase enzymes were also significantly less active during the EPR (5.5 +/- 0.7) than the LPR (9.9 +/- 2.3) and at baseline.
Histamine levels significantly correlated with allergic signs and symptoms (p < 0.05) only during the EPR.
Lodoxamide significantly reduced histamine release during EPR (p < 0.05), allergic signs and symptoms during both EPR (p < 0.001) and LPR (p < 0.005), and tear cytology counts during LPR. In conclusion, greater
histaminase activity may account for the smaller amount of tear
histamine generally found during LPR, while these
enzymes seem to play less of a role during the surge of histamine release and activity in the EPR.
Lodoxamide was shown to ideally inhibit various aspects of the
allergic reaction: clinical signs and symptoms in both the early and late phases, the primarily EPR-related peak of histamine release, and the primarily LPR-related changes in tear cytology.