I had my first Reclast infusion 10 days ago. The next day I developed a high fever, high pulse rate, high heart rate, rigors (uncontrolled full body shivering). I went to Mayo ER and was diagnosed with SIRS (Systemic Inflammatory Reaction Syndrome). I was admitted to the hospital and got out about 24 hours later.

SIRS is an immune system overreaction - a cytokine storm - and can be dangerous. The ER has to treat as if you have an infection (which I did the previous two times), so I got IV antibiotics as empiric treatment (as in "we don't know what's causing this, but we'd better do what often works"). I had a remarkable collection of screening tests for all sorts of pathogens (all negative).

I believe this reaction is really rare. I was expecting the not uncommon "few days of flu-like symptoms" so didn't go to the ER as soon as I should have.

Today, I'm still recovering - just tired.

But if you have a history of SIRS or sepsis (they are very closely related), this is a possible risk. But again, I think my case is rare - due to my tendency towards SIRS.