The dosimetry of carbon-14 labelled compounds: The metabolism of diet hylenetriamine pentaacetic acid (DTPA) in the rat

The metabolism of carbon-14 labelled diethylenetriamine pentaacetic acid has been studied after intravenous injection and pulmonary intubation in male rats in order to assess the likely radiation dose to man receiving this labelled drug. The carbon-14 was rapidly eliminated with 84% being excreted in the urine and 10% in the faeces during the first 24 hr after intravenous injection and 75% in the urine and 25% in the faeces over the same period after pulmonary intubation of [¹⁴C]DTPA. The cumulative excretion up to 9 days after administration was 99% of the injected activity. Tissue levels were below 1% of the administered activity at 24 hr and by 39 days after intravenous injection carbon-14 was detected only in the lung (0.002%), kidneys (0.007%) and bone (0.14%). The radiation doses calculated from the rat data for various organs in man are less than 100μSvMBq^-1 (0.4mrem μCi^-1) except for the lower large intestine which receives a radiation dose of 380 /gmSv MBq^-1 (1.4 mrem μCi^-1) after intravenous injection of [¹⁴C]DTPA and 730 μSv MBq^-1 (2.7 mrem μCi^-1) after [¹⁴C]DTPA is deposited in the pulmonary region of the lung.