| Abstract: | We used a rat model to study the effects of renal irradiation on the pharmacology of methotrexate (MTX) and cisplatinum (cis-Pt). Unanesthetized rats were given bilateral kidney irradiation (20 Gy in 9 fractions). At 9 months after irradiation, 3% of the animals had died and survivors showed moderately impaired renal function. At 15 months, 30% of the animals had died and survivors showed severely impaired renal function. Some animals were given i.v. MTX 1 week to 15 months after irradiation. In irradiated rats, the area under the MTX plasma clearance curve equaled that of controls through 6 months, and was significantly above controls from 9 months on. Other animals were given i.p. cis-Pt 1 week to 9 months after irradiation. The acute toxicity of cis-Pt was the same in control and irradiated rats when cis-Pt was given immediately before or after irradiation. Beginning 3 months after irradiation there was a progressive increase in cis-Pt toxicity and a simultaneous decrease in urinary platinum excretion. Irradiated animals that survived cis-Pt treatment showed increased radiation nephritis; the greatest effect occurred when cis-Pt was given 3 months or more after irradiation. MTX and cis-Pt clearance decreased when renal dysfunction was first observed and changes in renal function preceded changes in drug clearance and toxicity. |
