The effect of methylene diphosphonate on the tissue distribution of gallium-67

Nonradiolabeled methylene diphosphonate (MDP) was administered intravenously to CFW Swiss outbred female mice 2 hr prior to i.v. injection of [67Ga]citrate. The dose of MDP ranged from that usually administered for bone scanning (17.9 micrograms/kg) to 1,000 times the usual bone scan dose (17.9 mg/kg). The animals were killed 24 hr after administration of [67Ga]citrate and organ distribution determined as compared to control animals who received no MDP. At MDP doses one to ten times usual bone scan dose, the only organ showing significantly different 67Ga uptake was the lung and this difference in pulmonary uptake was accounted for by incidental pulmonary infection. At MDP doses 100 to 1,000 times usual bone scan dose, significantly altered 67Ga uptake was noted in lung, spleen, kidney, and gastrointestinal tract. The only consistent pattern of association of MDP administered dose and alteration in 67Ga uptake, however, was noted in the spleen where uptake was augmented with increased dose, and the bone where increased MDP dose depressed 67Ga uptake. Even this effect, however, was modest. It is concluded that at usual MDP dose levels used in bone imaging, no significant alterations occur in 67Ga distribution in normal mouse tissue. It is inferred that 67Ga scans performed following bone scans can be interpreted as if both radiopharmaceuticals had been administered separately.