In -vitro studies indicate that zoledronic acid is approximately 22% bound to plasma proteins. In -vitro studies also indicate that zoledronic acid does not inhibit microsomal CYP450 enzymes. In -vivo studies showed that zoledronic acid is not metabolized, and is excreted into the urine as the intact drug. However, no in -vivo drug interaction studies have been performed.
Caution is advised when bisphosphonates are administered with aminoglycosides, since these agents may have an additive effect to lower serum calcium level for prolonged periods. This effect has not been reported in Zometa clinical trials.
7.2 Loop Diuretics
Caution should also be exercised when Zometa is used in combination with loop diuretics due to an increased risk of hypocalcemia.
7.3 Nephrotoxic Drugs
Caution is indicated when Zometa is used with other potentially nephrotoxic drugs.
In multiple myeloma patients, the risk of renal dysfunction may be increased when Zometa is used in combination with thalidomide.
Clinical experience with acute overdosage of Zometa is limited. Two patients received Zometa 32 mg over 5 minutes in clinical trials. Neither patient experienced any clinical or laboratory toxicity. Overdosage may cause clinically significant hypocalcemia, hypophosphatemia, and hypomagnesemia. Clinically relevant reductions in serum levels of calcium, phosphorus, and magnesium should be corrected by intravenous administration of calcium gluconate, potassium or sodium phosphate, and magnesium sulfate, respectively.
In an open-label study of zoledronic acid 4 mg in breast cancer patients, a female patient received a single 48-mg dose of zoledronic acid in error. Two days after the overdose, the patient experienced a single episode of hyperthermia (38°C), which resolved after treatment. All other evaluations were normal, and the patient was discharged seven days after the overdose.
A patient with non-Hodgkin’s lymphoma received zoledronic acid 4 mg daily on four successive days for a total dose of 16 mg. The patient developed paresthesia and abnormal liver function tests with increased GGT (nearly 100U/L, each value unknown). The outcome of this case is not known.
In controlled clinical trials, administration of Zometa 4 mg as an intravenous infusion over 5 minutes has been shown to increase the risk of renal toxicity compared to the same dose administered as a 15-minute intravenous infusion. In controlled clinical trials, Zometa 8 mg has been shown to be associated with an increased risk of renal toxicity compared to Zometa 4 mg, even when given as a 15-minute intravenous infusion, and was not associated with added benefit in patients with hypercalcemia of malignancy [ see Dosage And Administration (2.4) ].