Allergy Medicines

Antihistamines
From humble beginnings as a remedy for seasickness, antihistamines were serendipitously found to have beneficial effects on allergy symptoms. Even now, most of the commercially available products for seasickness are antihistamine drugs. But over the years there have been tremendous strides made in the science of antihistamines.

An antihistamine is not actually the opposite of histamine. Rather, it is a drug (an antagonist) that binds to certain sites (receptors on cells) in the body, in order to prevent histamine from binding. Histamine must bind to these receptors in order to cause a response.

Histamine (the agonist) is produced naturally by the immune system and released in response to certain types of damage. Histamine causes inflammation by binding to H1 receptors on the smooth muscle cells within blood vessels causing them to dilate producing localized edema or swelling. When the body releases too much histamine, there is an increased dilation of the blood vessels and increased contraction of smooth muscle in the lungs (bronchoconstriction)--thus participating in an allergic reaction. Additional substances are released that contribute to the overall effect. The term antihistamine refers to a drug, which blocks H1 (histamine, type 1) receptors in the body.

Antihistamines compete for the H1 receptors on blood-vessel endothelial cells and smooth muscle cells. It is easier for the cells to bind the antagonist, because we can flood the body with more antihistamines than naturally produced histamine. This means that the drug uses up the H1 receptors and prevents excess histamine from binding to and affecting the lungs.

Currently, there are over-the-counter versions (first generation), minimally- and non-sedating versions available by prescription, intra-ocular (eye), and one intra-nasal spray form (second generation). First generation products include Benadryl, Dimetapp, Pedia-Care. Second generation antihistamines are Claritin, Zyrtec, and Allegra. Patanol is a prescription eye medication and Astelin is currently the only intra-nasal form.

       

Mast Cell Inhibitors
Another way to prevent the inflammation of allergies is to prevent the production or secretion of irritating chemical by the cells involved in the allergy process. These are the mast cells and eosinophils. Products in this category (notably cromolyn sodium) have been used for decades with no significant side effects. Nasal and Ocular (eye) versions are even available over-the-counter. Nonetheless, they are slow to take effect, requiring possibly 6 weeks of advance application, and have so little immediate effect that frequently patients give up daily use even if the drug is working. The most common product is NasalCrom.

Nasal Steroids
Often vilified, because of ignorance or confusion with oral version used in severe diseases, nasal steroids have long suffered from misunderstanding. Fortunately, in other countries the use of inhaled steroids has been more prevalent, allowing us to have tremendous experience to draw upon to verify the safety and effectiveness of these products. These products are the most potent anti-inflammatories on the block. They inhibit the production of numerous chemicals of many classes in a variety of cell types. While patients tell us that the onset of action is usually within a week, although the FDA usually requires the standard 7-14 day guideline as the official time to onset of symptom relief. Side effects have been found to be comparable in frequency to placebo for almost all the products, which indicates that the noted nosebleeds, nose pain, and headaches, are most likely due to the symptoms that are found in allergy sufferers and not due to the steroids. Also, long-term studies included actual biopsies of nostrils after a year of daily use of intra-nasal steroids. The mucosal lining of the nose was found to be much more normal appearing than that of patients without steroid treatment. No deleterious effects were found and there were NO indications that there were systemic effects such as slowing of growth. On the positive side, these products are not sedating nor are they habit-forming. Preliminary studies are being done to evaluate the possibility of releasing these steroids for over-the-counter use.

Examples of newer, more potent intra-nasal steroids include Flonase, Nasonex, and Rhinocort. While almost all are aqueous (water-based), Rhinocort is available, for the time being, as a dry powder inhaler. Older versions include Beconase, Nasarel, Nasacort, and Vancenase. These, however, suffer from issues of lower potency and higher absorption by the body.

      

November 2001