Gallium Nitrate for Acute Treatment of Cancer-related Hypercalcemia: Clinicopharmacological and Dose Response Analysis1

Current treatment of cancer-related hypercalcemia is limited by agents of limited effectiveness or excessive toxicity. Gallium nitrate is a new drug which both inhibits bone résorptionand increases calcium content of bone. We have now treated 39 episodes of hypercalcemia with gallium nitrate administered as a continuous i.v. infusion for 5-7 days at 3 daily dose levels (100 and 200 mg/m2, and 50 mg/m2 by brief infusion followed by 150 mg/m2). Nadir calcium values were significantly lower (9.2 ±1.5 mg/dl) for patients who received the highest dose relative to patients who received the lowest dose (10.5 ±1.6 mg/dl, /' < 0.001). While the actual percentage of patients who achieved normocalcemia was higher at the highest dose relative to the lowest dose (86 versus 60%), this difference was not statistically significant. Mean serum concentration of inorganic phosphorous declined significantly for all patients from 2.9 ±0.86 mg/ dl at base line to 1.8 ±0.66 mg/dl (/' < 0.001). Pharmacokinetic studies suggested that a threshold plasma gallium concentration of approximately I /Ji4ml must be attained to achieve acute normalization of elevated serum calcium levels. Steady-state plasma gallium levels were attained after 48 h; there was no evidence of drug accumulation in plasma after 2 days. Kffects on serum creatinine concentration were negligible, and there were no other toxic reactions. These data confirm preclinical experiments which suggested that inhibition of bone résorptionby gallium nitrate is dependent upon the dose and duration of drug exposure. We conclude that gallium nitrate is effective treatment for cancer-related hypercal cemia. The drug is now being evaluated against standard treatment in a randomized, double-blind trial.