5-(3-Methyltriazen-1-yl)-imidazo-4-carboximide (
MTIC) is a highly unstable compound which is believed to be the biologically active degradation product of the
antitumor agent temozolomide. An HPLC method has been developed and validated for the analysis of
MTIC in human plasma. Because of the instability of
MTIC, sample processing was kept to minimal. The method involved precipitation of
plasma protein with
methanol followed by analysis of the supernatant using reversed-phase column and UV detection at 316 nm. The linearity (r>0.99), precision (C.V.<9%) and accuracy (bias<5%) were satisfactory. The lower limit of quantitation (LOQ) was 10 ng/ml. The recovery of
MTIC and internal standard was > or = 86.7%.
MTIC was stable in plasma though three freeze-thaw cycles, and was stable at 4 degrees C for 1 h and at -80 degrees C for at least 70 days.
MTIC may be unstable
at 10 degrees C in processed samples; therefore, samples were placed in the autosampler (10 degrees C) immediately prior to injection. By using this analytical method,
MTIC was quantified in plasma of
cancer patients (n=12) within 0.25-12 h after
oral administration of
temozolomide at 150 mg/m2. The mean maximum plasma concentration (Cmax) was 211 ng/ml which was observed at a mean Tmax of 1.88 h post dose.
MTIC disappeared rapidly from plasma with an apparent in vivo half-life (t1/2) of 1.9 h similar to that of
temozolomide. Following in vitro incubation of
MTIC in human plasma at 25 degrees C,
MTIC disappearance was bioexponential with estimated t1/2 values of 25 and 60 min for the first and second phases, respectively. Therefore, the elimination t1/2 of
MTIC in human in vivo (1.9 h) was controlled by the rate of its formation from
temozolomide.