Disposition and pharmacokinetics of temozolomide in rat

Abstract

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 ¹⁴C-radiolabelled temozolomide. The distribution of ¹⁴C-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.