High-performance liquid chromatographic assay of mitomycin in biological fluids

Sensitive and convenient high-performance liquid chromatographic method for the determination of mitomycin C in human plasma

An improved high-performance liquid chromatographic assay for the cytostatic drug mitomycin C in plasma is presented. The principal steps are precipitation of plasma proteins with acetonitrile, lyophilization of the supernatant and reversed-phase chromatography on a Hypersil ODS 5 microm column with 0.01 M NaH2PO4 buffer (pH 6.5)-methanol (70:30, v/v) in isocratic mode. At a flow-rate of 1.3 ml/min a column pressure of 180-220 bar resulted. Porfiromycin served as internal standard. UV detection was performed at 365 nm. Quantitation limit based on a coefficient of variation <10% in intra- and inter-day assay was 5 microg/l mitomycin C, detection limit based on a signal-to-noise ratio of 3 was 1 microg/l. Recovery was 100% and linearity was shown for the whole range of concentration (1-500 microg/l). None of the five drugs used during chemoembolisation interfered with the assay in vitro. The assay meets the requirements for pharmacokinetic studies of mitomycin C in patients as regards sensitivity and ease of use.

Etoposide combined with interferon alfa-2b: novel exploitation of established etoposide pharmacokinetics and pharmacodynamics

PURPOSE

To construct an efficient pilot study design to determine whether interferon alfa-2b modifies the pharmacokinetics and pharmacodynamics of continuous-infusion etoposide.

PATIENTS AND METHODS

A two-stage randomized 2 X 2 factorial design was used to evaluate interferon alfa-2b at two doses (2 or 10 MU/m2/day SQ for 3 days) and two schedules (interferon alfa-2b administered before or concurrent with 72-hour continuous-infusion etoposide). Etoposide was administered at 75, 100, or 125 mg/m2/day. In lieu of comparing the experimental arms to an etoposide-alone control arm to determine effect of interferon alfa-2b dose and schedule, a novel analytic approach was used. The effect of interferon alfa-2b on etoposide-induced leukopenia was assessed indirectly by comparison of the observed white blood cell (WBC) nadir to the nadir predicted from an established pharmacodynamic model for single agent etoposide.

RESULTS

Based on 29 patients, dose-normalized 24-hour total and estimated free etoposide concentrations did not differ with interferon alfa-2b dose or schedule. Patients treated with interferon alfa-2b before etoposide had, on average a WBC nadir 545 +/- 225 cells microliter lower than that predicted by a pharmacodynamic model for etoposide alone. An optimal nonlinear model for leukopenia was defined by interferon alfa-2b schedule in addition to 24-hour etoposide concentration.

CONCLUSION

A novel study design and statistical analysis provided an efficient preliminary evaluation of the combination of interferon alfa-2b with etoposide in a modest number of patients. Exploitation of a previously validated pharmacodynamic model allowed evaluation of interferon alfa-2b effect and eliminated the need for an etoposide-alone control arm. The pharmacokinetics of continuous-infusion etoposide at doses from 75 to 125 mg/m2/day appear to be unchanged by interferon alfa-2b at the doses and schedules tested and the combination appears to be feasible. We hypothesize that leukopenia may be enhanced when interferon alfa-2b is administered before etoposide, especially at a higher dose of interferon alfa-2b.

A population model for the leukopenic effect of etoposide

We present a new model-dependent approach to quantify hematologic toxicity in a patient population after anticancer therapy. The population model consists of three submodels that are simultaneously fit to the data: (1) a cubic spline function describing the average response of the population versus time ("structural model"), (2) a covariate model, which relates parameters of the structural model to measured demographic or therapeutic variables that are found to be of predictive value (in this study: white blood cell (WBC) count baseline, drug concentration, serum albumin, and serum bilirubin concentration), and (3) a variance model, which estimates the contribution to the response from random variability between patients and from variability within patients, both between courses and within courses, between days. To demonstrate the approach, previously reported data from 118 courses of etoposide therapy in 71 patients with cancer were used to model the decrease in WBC count after 3-day continuous infusions of drug. The estimated typical response profile is characterized by (1) a lag-time of 4 1/2 days before any WBC count decline is observed, (2) a duration of time below baseline of 22 days, and (3) half-maximal effect (i.e., decrease to 50% of baseline WBC count) after exposure to C50 = 3 mg/L etoposide (mean) over 3 days. Lower serum albumin concentrations, higher bilirubin concentrations, or both are associated with greater effects at a given etoposide exposure. Large variability in the estimated response was found between individuals and within individuals, between courses. The total variabilities (SD) in lag-time, duration of the decrease, and C50 were 1 day, 6 days, and 1.8 mg/L, respectively. The population model can also be used to predict the consequence of as-yet untested therapy and sampling strategies, as well as to relate acceptable risks of toxicity to target drug exposure.

Determination of mitomycin C in human aqueous humor and serum by high-performance liquid chromatography

Mitomycin C (MMC) is used in the treatment of disseminated adenocarcinoma of the stomach and pancreas and is used in ophthalmology as adjunctive therapy in trabeculectomy. Since only small volumes of aqueous humor are available for analysis, a sensitive method requiring limited sample preparation was developed. An internal standard, 4-aminoacetophenone, was added to aqueous humor specimens, and the solution was directly injected into the high-performance liquid chromatographic (HPLC) column. The use of a short 50-mm C18 reversed-phase column gave adequate resolution of peaks with improved sensitivity. The method was applicable for determination of MMC in serum, although solid-phase extraction for sample clean-up was required prior to injection into the HPLC column, and analytical columns of 150-250 mm were necessary for adequate resolution of peaks. The method has been validated and is linear from 6.25 to 50 ng/ml in aqueous humor and from 10 to 500 ng/ml in serum.

Chromatographic analysis of anticancer drugs

The present review on the methods for the analysis of anticancer drugs should be seen as an addition to the excellent work of Eksborg and Ehrsson published half a decade ago in this journal (Vol. 340, p.31). The style and format have been followed closely, with the focus again on chromatographic techniques. We felt it important to add a list of compound (group) structures as a service to the reader. Methods have been reviewed for alkylating agents, platinum compounds, antitumour antibiotics, antimetabolites, alkaloids, suramin, 1-hydroxy-3-amino-propylidene-1,1-bisphosphonate and tamoxifen.