I've read that 1% of Reclast patients experience Cytokine Storm Reaction. 30% and 40% in different studies experience a lesser APR 1 to 3 week reaction. Explained in this way:
"When amino-bisphosphonates (N-BPs) are administered IV, resulting in a high systemic exposure (unlike when taken orally, where the very low oral bioavailability results in a quite low systemic exposure), phagocytic cells other than just osteoclasts can encounter the N-BP, Up to 30% of patients can experience an APR (acute phase reaction) after their initial infusion of zoledronic acid. This APR, which starts usually about 6 hours post-infusion, and can last several days, consists of a mild fever associated with muscle and joint pains, similar to the symptoms with a bad viral infection such as the flu. And it turns out that the cause is very similar, as well. When a special category of phagocytic T-cells, called gamma-delta T-cells, encounter the zoledronic acid, they engulf it, just like an osteoclast will engulf alendronate or zoledronic bound to the bone surface. And just like an osteoclast that engulfs a N_BP undergoes apoptosis (programmed cell death), the gamma-delta T-cells that engulfs a N-BP also undergoes apoptosis. The difference is, when a gamma-delta T-cell undergoes apoptosis, it releases inflammatory cytokines, such as IL-1, IL-6, and TNF-alpha, just like when it encounters a flu virus. And these inflammatory cytokines mediate the temperature rise and myalgias, just as with a flu infection."

Advice from an anonymous. expert who has treated many patients with IV zoledronic acid and played a key role in the development of Fosamax, oral and IV Boniva

"There are 3 things I routinely do when I treat patients with IV zoledronic that not all physicians understand. First, I order the infusion to dilute the 5 mg of zoledronic acid (which comes in 100 mL of D5W) into 500 mL of NS (normal saline), thereby diluting the drug from 5 mg% to 0.8 mg%. Then I order it to be administrated over 60 minutes, instead of 15 minutes. Giving an N-BP more dilute and more slowly makes it even safety for the kidneys. The 3rd thing I always do is order the infusion nurses to administer 650 mg of acetaminophen to the patient during the infusion, and I tell the patient to take at home the same dose of acetaminophen (two regular strength Tylenols) with dinner and at bedtime the day of the infusion, with all 3 meals and at bedtime the day after the infusion, and a final (7th) dose with breakfast the 2nd morning after the infusion. These 8 doses total of acetaminophen reduce the chance of a symptomatic APR from 20-30% to < 1%.The other thing to consider is that in most patients, a 5 mg infusion of zoledronic acid will control the rate of bone turnover for at least 24 months, so most of my patients do not get annual infusions."