HISTAMINE ANTAGONISTS The effects of histamine released in the body can be reduced in several ways. Physiologic antagonists,especially epinephrine,have smooth muscle actions opposite to those of histamine,but they act at different receptors.This is important clinically because injection of epinephrine can be lifesaving in systemic anaphylaxis and in other conditions in which massive release of histamine and other mediators occurs. Release inhibitors reduce the degranulation of mast cells that results from immunologic triggering by antigen-IgE interaction.Cromolyn and nedocromil appear to have this effect and are used in the treatment of asthma,though the molecular mechanism underlying their action is presently unknown.Beta2-adrenoceptor agonists also appear capable of reducing histamine release. Histamine receptor antagonists represent a third approach to the reduction of histamine-mediated responses.For over 60 years,compounds have been available that competitively antagonize many of the actions of histamine on smooth muscle. However,not until the H2-receptor antagonist burimamide was described in 1972 was it possible to antagonize the gastric acid-stimulating activity of histamine.The development of selective H2-receptor antagonists has led to more effective therapy for peptic disease.Selective H3 and H4 antagonists are not yet available for clinical use. However,potent and selective experimental H3-receptor antagonists,thioperamide and clobenpropit,have been developed. PREPARATIONS AVAILABLE ANTIHISTAMINES (H BLOCKERS)* Azelastine Nasal (Astelin):137 mcg/puff nasal spray Ophthalmic (Optivar):0.5 mg/mL solution Brompheniramine(generic,Brovex) Oral:6,12 mg extended release tablets;12 mg chewable tablets;8,12 mg/5 mL suspension Buclizine(Bucladin-S Softabs) Oral:50 mg tablets Carbinoxamine(Histex,Pediatex) Oral:4 mg tablets;8 mg timed-release tablets;10 mg extended release capsules; 1.5,4 mg/5 mL liquid;3.6 mg/5 mL oral suspension Cetirizine(Zyrtec) Oral:5,10 mg tablets;5,10 mg chewable tablets;5 mg/5 mL syrupHISTAMINE ANTAGONISTS The effects of histamine released in the body can be reduced in several ways. Physiologic antagonists, especially epinephrine, have smooth muscle actions opposite to those of histamine, but they act at different receptors. This is important clinically because injection of epinephrine can be lifesaving in systemic anaphylaxis and in other conditions in which massive release of histamine and other mediators occurs. Release inhibitors reduce the degranulation of mast cells that results from immunologic triggering by antigen-IgE interaction. Cromolyn and nedocromil appear to have this effect and are used in the treatment of asthma, though the molecular mechanism underlying their action is presently unknown. Beta2-adrenoceptor agonists also appear capable of reducing histamine release. Histamine receptor antagonists represent a third approach to the reduction of histamine-mediated responses. For over 60 years, compounds have been available that competitively antagonize many of the actions of histamine on smooth muscle. However, not until the H2-receptor antagonist burimamide was described in 1972 was it possible to antagonize the gastric acid-stimulating activity of histamine. The development of selective H2-receptor antagonists has led to more effective therapy for peptic disease. Selective H3 and H4 antagonists are not yet available for clinical use. However, potent and selective experimental H3-receptor antagonists, thioperamide and clobenpropit, have been developed. PREPARATIONS AVAILABLE ANTIHISTAMINES (H1 BLOCKERS)* Azelastine Nasal (Astelin): 137 mcg/puff nasal spray Ophthalmic (Optivar): 0.5 mg/mL solution Brompheniramine (generic, Brovex) Oral: 6, 12 mg extended release tablets; 12 mg chewable tablets; 8, 12 mg/5 mL suspension Buclizine (Bucladin-S Softabs) Oral: 50 mg tablets Carbinoxamine (Histex, Pediatex) Oral: 4 mg tablets; 8 mg timed-release tablets; 10 mg extended release capsules; 1.5, 4 mg/5 mL liquid; 3.6 mg/5 mL oral suspension Cetirizine (Zyrtec) Oral: 5, 10 mg tablets; 5, 10 mg chewable tablets; 5 mg/5 mL syrup