Interference of antihistamines and anti-allergic drugs with antigen-induced paw edema in boosted and unboosted mice.

The protective effects of two antihistamines and two anti-allergic drugs against anaphylactic paw edema were studied in immunized animals that had or had not received a booster injection of antigen. The injection of 1 or 10 micrograms/paw ovalbumin induced acute paw edema of similar intensity in both groups. The antihistamine meclizine and the mixed anti histamine/anti-5-HT antagonist cyproheptadine reduced the anaphylactic reaction by 55 and 84% respectively, in non-boosted animals and were less effective against edema induced by 1 microgram antigen in boosted animals. The effectiveness of these drugs was also reduced when boosted mice were challenged with 10 micrograms antigen, where meclizine and cyproheptadine inhibited edema by 31 and 59%, respectively. The anti-allergic compounds ketotifen and azelastine, although effective against allergic inflammation in non-boosted mice, had a reduced or no effect in boosted mice. Our results suggest that allergic edema is less sensitive to antihistamine and anti-allergic drugs in boosted mice, which may be accounted for by an increased role of other mediators.