Thank you for your inquiry.
First of all, it is important to note that there is no definite answer to your questions. The best source of information is the most recent insect sting parameter edited by Dr. David Golden (1).
I have copied below, for your convenience, a few quotes from this parameter dealing with the duration of immunotherapy to fire ant venom.
"The optimal duration of fire ant immunotherapy is less well defined. Most allergists consider stopping fire ant immunotherapy after a specified period (usually 3-5 years) either empirically or only when skin test or in vitro test results become negative. 55 Until further data are available, a definitive recommendation about the duration of immunotherapy for fire ant sting allergy cannot be made."
"The optimal duration of imported fire ant immunotherapy has not been clearly established. Skin reactivity appears to be a poor indicator of the risk for a systemic reaction to fire ant venom after fire ant immunotherapy. As a result, there is a great deal of variation in recommendations regarding the duration of immunotherapy for fire ant allergy, with some allergists recommending
indefinite treatment. Most allergists recommend stopping immunotherapy after a specific period (usually 3-5 years), either empirically or when skin test responses become negative."
“The optimal duration of imported fire ant immunotherapy is less well defined. One retrospective survey suggests an equal risk of a sting reaction whether a patient received more than 3 years of immunotherapy or less than 3 years of immunotherapy, although the numbers were small. A survey of allergists indicated a great deal of variation in recommendations regarding the duration of immunotherapy for fire ant allergy.”
“Some allergists recommend indefinite treatment. Most allergists consider stopping immunotherapy after a specified period (usually 4-5 years), either empirically or only when skin test responses become negative. Until further data are available, a definitive recommendation.... cannot be made."
As you can see, we do not have enough data available to determine a specific time at which to stop venom immunotherapy, nor do we have enough data for you to clearly state a specific risk of anaphylaxis to a repeat sting. Therefore, the only thing that you can tell the parents is that we do not have enough information for us to predict with any accuracy what the prognosis will be should we stop venom immunotherapy. When reaching this point in immunotherapy to fire ant, all that one can offer to the patient is a frank discussion of risks and of our lack of definitive knowledge in this regard.
My personal recommendation, more often than not, is to continue venom therapy with a gradual attempt to lengthen the duration of time between injections. However, as you can see from the quotes copied above, that opinion is not based upon any consensus or evidence.
The other issue, which may give you some solace, is that we do not have enough information available to state that because this child’s venom-specific IgE remains elevated that she is at greater risk than a child in whom the venom-specific IgE has markedly declined. It is true that specific IgE to venom does decline in most studies of venom immunotherapy to flying hymenoptera, but it is not completely clear whether this applies to fire ant. In addition, specific IgE does not decline in all patients (2).
Thank you again for your inquiry and we hope this response is helpful to you.
1. Golden D, et al. Stinging insect hypersensitivity: a practice parameter update 2011. J Allergy Clin Immunol
2. Golden D, et al. Prospective observations on stopping prolonged venom immunotherapy. J Allergy Clin Immunol
Phil Lieberman, M.D.