Mitomycin C pharmacokinetics in patients with recurrent or metastatic colorectal carcinoma

The pharmacokinetics of mitomycin C as a single agent have been determined in 25 treatment courses given to 18 patients with recurrent or metastatic colorectal carcinoma using a high performance liquid chromatography (HPLC) assay to analyze plasma and urine samples. The plasma pharmacokinetics conformed to a two-compartment linear model in 21 of 25 courses monitored with a mean t 1/2 λ₁ of 9.8 ± 1.2 (SEM) min and mean t 1/2 λ(z) of 64.1 ± 8.9 (SEM) min. The large variation observed in r 1/2 λ(z) was not related to dose or treatment, but an interaction of these two factors approached significance (p = 0.057). Renal excretion in the 12 courses in which it was determined averaged only 2.3% of the total administered dose during the first 4 h monitored and no mitomycin C metabolites were detected in plasma or urine by the HPLC technique used. The most common toxicity, thrombocytopenia, did not correlate with t 1/2 λ(z) or the area under the curve. This may be due to (i) a failure to monitor active metabolites of mitomycin C; (ii) other factors besides plasma drug concentrations that mediate toxicity towards marrow elements; or (iii) the small number of courses associated with thrombocytopenia (< 100 000/mm³). Our study indicates that (i) an interaction of drug dose and treatment course may be associated with increasing t 1/2 λ(z); (ii) the renal clearance contributes a small component of mitomycin C elimination; (iii) metabolites of mitomycin C cannot be detected by the present HPLC technique; and (iv) routine monitoring of mitomycin C using present methods cannot be recommended for clinical use to predict toxicity.