How Histamine Impacts Your Asthma

Histamine is the chemical that is found in and released by mast cells that can lead to certain symptoms depending on the part of the body where the histamine release occurs:

• Nose: runny nose
• Eyes: itchy, watery
• Throat: sore, scratchy
• Lung: wheezing, chest tightness, shortness of breath, and cough

Histamine is an immune system mediator or, more simply, a chemical messenger that helps direct your body's response to a foreign invader. Histamine tells your body's natural defense mechanisms how to react to something it perceives as foreign. In asthma and allergy, your body is over-reacting to something that is not particularly harmful but has caused your immune system to react. Histamine functions as a vehicle of communication between different parts of the immune system.

In asthma, histamine promotes bronchoconstriction and production of mucus.

Histamine is released from mast cells and basophils when you are exposed to allergens. When histamine is released, the allergic response begins. Antihistamine drugs are used in the treatment of the allergic symptoms caused by the release of histamine. Some popular anti-histamine medications include:

• Zyrtec
• Allegra
• Claritin
• Benadryl

Another class of drugs that address some of the consequences of histamine are the leukotriene modifiers. These drugs relieve bronchoconstriction and decrease mucus production and additionally decrease edema or swelling as well as the production of eosinophils as part of the pathophysiology of asthma.

These drugs are relatively well tolerated by patients and many studies report better adherence to this treatment compared to other asthma treatments. Most of their drug labels recommend periodic lung function testing, which should already be part of your asthma care plan. Additionally, there have been some noted interactions with the blood thinner warfarin as well as behavioral changes noted in adolescents. While depression was seen more commonly in treated adolescents, there was not an increase in actual suicides noted.

Multiple studies have demonstrated a bronchodilatory effect as well as improvement in asthma symptoms. Other important outcome measures noted decreased use of rescue inhalers, as well as decreased asthma exacerbations and episodes requiring oral steroids like prednisone. However, these drugs do not appear to be as effective as inhaled steroids for your asthma. A number of different studies have demonstrated improvements in lung function are superior with inhaled steroids, fewer exacerbations occur, and patients experience more symptom-free days. As a result, national guidelines clearly recommend inhaled steroids as a first-line treatment when you need more than a rescue inhaler.

It is well known that patient adherence to inhaled steroids is suboptimal, and most studies have demonstrated superior patient adherence to once-daily montelukast compared to inhaled steroids in both children and adults. Parents are often concerned about the side effects of inhaled steroids and they are often underprescribed by doctors.

The superior adherence to montelukast may explain its comparable beneficial effects on asthma control to those of inhaled GC in some "real-world" studies. Despite the importance of this issue in clinical practice, it is largely circumvented in clinical trials, studies that lead to drug approval by the FDA,  by having study coordinators provide frequent reminders to patients and by excluding those patients whose adherence (as documented by electronic monitors built into the inhaler devices) is poor.

It is also apparent that primary care clinicians tend to under-prescribe inhaled steroids. Thus, no matter how efficacious inhaled steroids may be, their utility in real-world settings is limited by inadequate prescribing and adherence.

While not the preferred choice based upon current asthma guidelines, leukotriene modifiers are a reasonable approach as a first-line controller agent for patients who either will not take or cannot tolerate inhaled steroids. Validation of this approach is supported by a so-called “pragmatic” trial conducted in 306 patients managed in primary care practices, in which montelukast was demonstrated to be comparable to inhaled steroids as a first-line controller therapy.