Thank you for your inquiry.
Before directly responding to your question, I would like to make a potentially important point. First of all, to the best of our knowledge at this time, fire ants are not present in Africa. They are found in America, South America, Puerto Rico and perhaps other Caribbean locations, China, Taiwan, Australia, and New Zealand. However, there are other ants that can cause anaphylaxis, and it is highly possible that such are located in Africa. Also, there are definite gaps in our knowledge as to the potential cross-reactivity between all ants capable of causing anaphylaxis.
Therefore, there is some solace in that at least according to our present knowledge fire ants are not found in Africa. However, because of the fact that other species cause reactions, and there may be cross-reactivity between the venoms, one cannot completely be reassured that a reaction could not have occurred due to the bite of an African ant.
Unfortunately because of the factors discussed below I can't give you a definite answer as to the duration of protection produced by epinephrine but van say the following:
1. The onset of action of epinephrine is quite rapid when administered properly, intramuscularly, in the lateral thigh using an automatic epinephrine injector. The onset of action can be within 5 to 10 minutes, and the maximal effect is usually obtained within 20 minutes. However, it is also rapidly metabolized and in some instances, its effects can disappear within 15 to 20 minutes as well.
2. It is felt that the earlier epinephrine is administered, the better the chance to prevent a severe reaction.
3. A second dose can be administered within 5 to 10 minutes of the first dose if improvement has not occurred.
4. In some instances where a medical facility cannot be reached, a patient can self-administer a third dose within 10 to 15 minutes of the second.
5. Based on the above, it is not clear as to how long a patient has to reach an emergency facility because of variations in the catabolism of the drug from patient to patient as well as variations in the severity of the attack. It has been shown that fatalities can occur even when epinephrine is administered appropriately and in a timely fashion.
6. There is a preventive, desensitization program available to treat fire ants and thus minimize the recurrence of a reaction. Your student should proceed with desensitization if at all possible.
Thus, in summary, the injection should be given as soon as the patient is bitten or feels symptoms. Any patient should be equipped with multiple doses of epinephrine. We know that the onset of action would be rapid, but because of variations in the catabolism of epinephrine and the severity of events, we cannot give you a definite time as to how long the protective effect of epinephrine will last.
Finally, I believe it would be wise for your student to seek help from an allergist who performs desensitization to fire ant. You can find the location of a member or Fellow of the Academy here.
Thank you again for your inquiry and we hope this response is helpful to you.
1. Lieberman P, Nicklas R, Oppenheimer J, Kemp S, Lang D, et al. The diagnosis and management of anaphylaxis practice parameter: 2010 Update. In: Journal of Allergy and Clinical Immunology 2010 (September); 126(3):477-480 e42.
2. Klotz. Adverse reactions to ants other than imported fire ants. Annals of Allergy, Asthma, and Immunology 2005; 95:418-425.
3. Stigelman DA and Freeman TM. Imported fire ant allergy: case presentation and review of incidence, prevalence, diagnosis, and current treatment. Annals of Allergy, Asthma, and Immunology 2013; 111(4):242-245.
Phil Lieberman, M.D.