Disposition and pharmacokinetics of temozolomide in rat

1. Temozolomide, an imidazotetrazine derivative, is a cytotoxic alkylating agent of broad-spectrum antitumour activity. The absorption, metabolism, distribution and excretion of temozolomide have been investigated in male and female Sprague-Dawley and Long-Evans rats following single oral or intravenous dose administration of 200 mg m(-2) non-radiolabelled or (14)C-radiolabelled temozolomide. The distribution of (14)C-temozolomide was also evaluated by whole-body autoradiography in male Sprague-Dawley rats. Plasma concentrations of temozolomide and its active metabolite 3-methyl-(triazen-1-yl)imidazole-4-carboxamide (MTIC) were determined by high-performance liquid chromatography (HPLC) with ultraviolet detection. Plasma, urine and faeces were profiled by HPLC with radiochemical detection. 2. Temozolomide was rapidly and extensively (>90%) absorbed and widely distributed in tissues. The distribution pattern of radioactivity was gender independent. Penetration into the brain following oral or intravenous administration was 35-39% based on the brain/plasma AUC ratio. 3. Following intravenous or oral administration, temozolomide was primarily eliminated renally (75-85% of the dose) as either unchanged drug, a carboxylic acid analogue, AIC (a degradation product) and a highly polar unidentified peak. Biliary excretion was minimal (1.4-1.6%). The pharmacokinetics (oral versus intravenous) were similar and gender independent. The absolute oral availability was 96-100%. Temozolomide was rapidly eliminated (t(1/2) = 1.2 h) and converted to MTIC. 4. Systemic exposure to MTIC was about 2% that of temozolomide. Overall, the disposition of temozolomide in rats was similar to that observed in humans.