Need 2nd dose: Usually, anaphylaxis (& allergic reactions) requires a SECOND exposure to the foreign substance. The first exposure, which could be decades ago, "primes" the immune system. The second & subsequent exposures cause anaphylaxis. However, methycobalamine (Vitamin B12) is a natural & necessary vitamin, so if u react, it wd b from a preservatives or excipient in the injection. There r few other side eff
Answered 9/22/2014
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