There are many ways to try to adjust allergen-specific immunotherapy:
- Change the volume of antigen solution and, therefore, the total amount of protein injected.
- Change the interval between injections so that injections are given more frequently or less frequently.
- Along with giving the original set of antigens, start additional therapy by using a second set of antigens containing either
other allergens the pet is allergic to or a combination of some of the original antigens and new antigens.
- Remix or reformulate the antigens to adjust the concentration of antigen (protein level/volume) and the ingredients in each
set of antigen.
Most commonly, I change the volume of antigen solution injected or the frequency of the injections. My rule of thumb for injections
is to try to reach an average dose of 0.1 ml/day. If a dog is not responding or is responding well, then I will slowly reduce
the average dose to 0.05 ml/day. Initially, if the injection interval is between 10 and 20 days, then I will keep the dose
at 1 ml (e.g. an average dose of 0.1 to 0.05 ml/day) unless there are reactions correlated with the injections. If injections are given
less often than every 10 days, then the dog does not receive the full 1 ml. Dogs that receive injections every five days usually
get 0.5 ml or less. If dogs are on a seven-day injection interval, the most that should be given is 0.7 ml. However, occasionally
I will give more than this dose but it will be a gradual increase, not a sudden one.
Reasons to adjust allergen-specific immunotherapy after the first four months vary but mainly relate to improving efficacy
or decreasing adverse reactions. Animals that have not had any adverse reactions and slight but insignificant improvement
after four months are given injections at 10- to 14-day intervals. If they still do not respond by six months, then the volume
is lowered to 0.7 ml. If they still do not respond and no pattern is seen, the dosage is changed to 0.5 ml every five to seven
days. If there is still no response when those allergens are about gone, consider a new formulation or combination of two
formulations.
More commonly, an animal improves after an injection but its clinical signs recur before the next injection is due. In these
cases, the frequency of injections is decreased to prevent that increase in clinical signs. Other patients get worse after
an injection and then improve, only to start getting worse before the next injection. In these cases, both the volume of antigen
and the frequency of injection are decreased. In general, my goal is to find the highest volume that will not cause an increase
in clinical signs. Once this goal is accomplished, then the injection frequency is adjusted so that the improvement is maintained
the whole time. In some cases in which the frequency cannot be lengthened even at the highest tolerated volume, the frequency
is changed to the longest time the pet stays improved and the volume is adjusted, with an average of 0.1 ml/day being the
maximum dose.
To transition to a maintenance dose, I keep the dose administered the same, but the number of days between each injection
increases. I usually will try to get the maintenance dose to average out to about 0.05 ml/day, and most dogs end up receiving
an average of 0.03 ml/day to 0.1 ml/day. Knowing the range of the average daily doses makes it easy to predict the range of
what it will cost long-term for the allergen-specific immunotherapy, as that equates closely to 1 to 3 ml a month. The cost
of therapy will then be the amount you charge per milliliter, times one to three, plus the cost of syringes based on the frequency
of injections per month. When the pet has an excellent response with total control (15% to 20% of cases), then only this cost
and one recheck per year is what the owners will spend on controlling their pets' atopic disease.
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