Thank you for your inquiry.
The questions you pose have no definitive answers, and my guess is that you would get different responses from various allergists-immunologists. I do not believe there is any literature which we could use to substantiate a response. Thus, I can only give you an opinion. This opinion would be neither right nor wrong, but only represent how I might deal with this difficult situation.
First of all I think your approach is reasonable and have no "better way".
Having said this, I would not continue preventive therapy once your patient leaves your office, but would simply observe her closely during the treatment.
I of course cannot tell for sure, but based upon your description, the side effects she has had to date have not been threatening, and I believe you would have time to institute therapy if symptoms did occur. If these symptoms were mild and responded to treatment with antihistamines and/or corticosteroids, I would consider treating through the reaction.
So in summary, I would personally not pretreat, but observe for a reaction; and if the reaction was not threatening, continue therapy until the full course of antibiotics had been administered.
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.