Clinical research update: zoledronate

The prolonged administration of bisphosphonates can reduce the frequency of morbid skeletal events in patients with metastatic breast carcinoma or multiple myeloma. The development of more potent bisphosphonates will simplify current therapeutic schemes and could improve the therapeutic effectiveness of bisphosphonate therapy. Zoledronate (CGP-42446) is the most potent of the clinically tested compounds. It is a cyclic third-generation bisphosphonate that is 100-850 times more active than pamidronate in several in vivo and in vitro pharmacological test systems. The first therapeutic trial with zoledronate has been performed in patients with tumor-induced hypercalcemia (corrected calcium [Ca] > 2.75 mmol/L after rehydration). In a Phase I multicenter trial, it was shown that a single infusion was already effective at dose levels of 0.02 and 0.04 mg of zoledronate/kg bodyweight, thus 1.2 and 2.4 mg total dose for an average 60-kg individual. Five of 5 patients became normocalcemic after a dose of 0.02 mg/kg, and 14 of 15 (93%) after a dose of 0.04 mg/kg. The median time to normalization of serum Ca was 2 days and the median duration of action was 33 days, suggesting that zoledronate has a faster onset and a longer duration of action than other clinically tested bisphosphonates. Zoledronate was well tolerated; the only side effect was an increase in body temperature in 30% of the cases, which was probably not drug-related in many patients. A Phase I trial also has been initiated in patients with lytic bone metastases. Zoledronate was given as monthly short infusions (5-30 minutes) at doses between 0.1-8.0 mg. There was an analgesic effect and even at low doses (2 mg and above), the effects on the biochemical markers of bone resorption appeared to be greater than after 90-mg pamidronate infusions. These initial human data suggest that zoledronate can be administered as convenient short intravenous infusions and lead to a more marked and a more prolonged inhibition of bone resorption than is currently possible with available compounds. Future trials will have to determine whether prolonged treatment with this extremely potent bisphosphonate also can have a greater effect on the morbidity of bone metastases.