Minocycline serum sickness but not Doxycycline???

Does anyone know why I might have a reaction to Minocycline but not Doxycycline?  I know that they are in the same family.

I took Vibramycin/Doxycycline for about a year for acne with no serious adverse effects other than some stomach upset. 

My doctor switched me to Minocycline to try and reduce the stomach upset.  About 8 days after starting the Minocycline I developed serum sickness/serum sickness like reaction.  I had some hives at first, for which I took 2 Benadryl caplets every 4 hours.  12 hours later, I developed angioedema and severe joint pain in my feet and hands.  I actually could not walk at this point, because the swelling and joint pain in my toes/feet was so bad.  The hives started to spread to my neck and face and I began to get dizzy/lightheaded around the same time.  I used my epipen at that time (which I had for a food allergy--sunflower seeds/oil) and continued with the benadryl.  My doctor then prescribed prednisone--5 days at 2x20mg tablets and 3 days at 1x20mg tablet. 

I am on day 2 of the prednisone and continued benadryl, and thank goodness the swelling is almost completely gone.

I know that the food allergy did not play a part--I am religious about label reading and sticking with 'safe' foods.

My question is--why did I have reaction like this to minocycline but not to doxycycline?  Does this mean that I can never take doxycycline again?  What is different about these two drug's makeup that would cause a reaction in one but not the other?