Medications for Allergy

Standard allergen immunotherapy is administered as a subcutaneous injection. The allergist selects the appropriate allergen extracts (vaccines) based on the patient’s clinical history, allergen exposure history, and the results of tests for allergen-specific IgE antibodies. The immunotherapy vaccine should contain only clinically relevant allergens. When preparing mixtures of allergen vaccines, the prescribing physician must take into account the cross-reactivity of allergens, the optimal dose of each constituent, and the potential for allergen degradation caused by proteolytic enzymes in the mixture. The efficacy of immunotherapy depends on achieving an optimal therapeutic dose of each allergen in the vaccine.

Allergen immunotherapy dosing consists of two treatment phases: the buildup phase and the maintenance phase. The prescribing physician must specify the starting immunotherapy dose, the target maintenance dose, and the immunotherapy buildup schedule. The highest concentration of vaccine projected to provide the thera-peutically effective dose is called the “maintenance” dose or concentrate. In general, the starting immunotherapy dose is 1000- to 10,000-fold less than the maintenance dose. For highly sensitive patients, the starting dose may be even lower. Dilute concentrations are more sensitive to degradation and lose potency more rapidly than the more concentrated preparations. Thus their expiration dates are much shorter and must be closely monitored.

The buildup phase involves injections with increasing amounts of allergens. The frequency of the injections can vary depending on the protocol. The most common or “conventional” protocol recommends dosing once to twice a week with at least 2 days between injections. It is customary to repeat or reduce the dose if there has been a substantial time interval between injections. Patients with greater sensitivity may require a slower buildup phase to prevent systemic reactions. With this schedule, maintenance is usually achieved after 3 to 6 months. Alternative schedules such as “rush” or “cluster” immunotherapy rapidly achieve maintenance dosing and should only be administered by an allergist/immunologist because of an increased risk for systemic reactions. Immunotherapy dosing schedules should be written by trained allergists/immunologists, and primary care physicians should seek their advice if questions or issues arise during administration.

The maintenance phase begins when the effective therapeutic dose is achieved. This final dose is based on several factors, including the specific allergen, the concentration of the extract, and how sensitive a patient is to the extract. Once maintenance is achieved, the intervals for injections range from every 2 to 6 weeks but are individualized for each patient. Clinical improvement can be demonstrated shortly after the patient reaches his or her maintenance dose. If no improvement is noted after 1 year of maintenance therapy, a reassessment should be done.

Table. Conventional immunotherapy.

Table. Typical buildup schedule for conventional immunotherapy.

Possible reasons for lack of efficacy need to be evaluated, and if none are found, discontinuation of immunotherapy should be considered. Patients should be evaluated at least every 6 to 12 months while on immunotherapy by the prescribing allergist/ immunologist. Duration of maintenance therapy is generally 3 to 5 years. Treatment may lead to prolonged clinical remission and persistent alterations in immuno-logic reactivity. The severity of disease, benefits from sustained treatment, and the convenience of treatment are all factors that are considered when deciding the length of therapy for each individual patient.

Many studies, especially from Europe, have shown that high-dose sublingual allergen immunotherapy is effective for certain patients, but this mode of therapy is not approved by the U.S. Food and Drug Administration and is considered investigational. Many questions still  remain   unanswered   on   sublingual

immunotherapy including effective dose concentrations, schedule for buildup and maintenance therapy, and timing of dosing (i.e., seasonal or continuous throughout the year). Additionally, sublingual therapy requires much larger doses of allergen, anywhere from 10 to 300 times greater, making cost an issue. Finally, the utility of sublingual immunotherapy for polysensitized patients is not yet determined.

This entry was posted on Friday, June 24th, 2011 at 5:34 am and is filed under Allergen Immunotherapy. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.