Lessons learned from long-term side effects after zoledronic acid infusion following denosumab treatment: a case report and review of the literature

Zoledronic acid is an intravenous, highly potent aminobisphosphonate for use in patients with primary or secondary osteoporosis. Zoledronic acid-induced prolonged side-effects are well known and quite common. However, severe side-effects can be a threat to life. We report a case of severe side-effects induced by zoledronic acid infusion, and its positive effect on long-term back pain.

In 2012, a 62-year-old white native Finnish woman was operated on for an estrogen and progesterone receptor-positive breast cancer. After radiotherapy, an aromatase inhibitor (letrozole) was started. Nine months after the operation, the patient suffered a low-energy compression fracture of Th XII. She received denosumab to prevent fragility fractures and to improve bone mineral density. Letrozole was discontinued after 5.5 years, and the last denosumab injection was given after 7 years. Six months later, at the age of 71 years, the patient received a single intravenous zoledronic acid infusion. Suddenly, at 10 hours from the infusion, she complained of severe trismus, muscle twitching, spasms, and tingling, matching hypocalcemia and several other symptoms. Her serum 25-hydroxyvitamin D concentration was high (163 nmol/L), the concentration of serum calcium and calcium-ion was normal (2.32 mmol/L and 1.23 mmol/L, respectively). However, the neutrophil to lymphocyte ratio (NLR) was low (1.6). A complete recovery took 2 months. Zoledronic acid infusion also had a positive effect: for many years, the patient had suffered low back pain and strain, which came to an end after this single infusion.

It is important that the potential patients receive sufficient information about the possibility of side-effects following the administration of intravenous zoledronic acid. To ensure that a zoledronic acid infusion is given as safely as possible, the safety information should include that the patient should not be left without monitoring for a minimum 24 hours after the infusion. Being alone and experiencing serious side-effects may lead to acute cardiac problems. Furthermore, the chronic low back pain and strain that our patient suffered for many years has clearly reduced for 16 months after infusion, so far. We conclude that this is a positive effect of zoledronic acid.